From c47362b08509388ab465c4e441f88b463bbbcc49 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12@gmail.com>
Date: Thu, 6 Nov 2025 16:27:22 +0000
Subject: [PATCH 1/4] [lldb][docs][NFC] Fix ClangModulesDeclVendor::AddModule
 parameter docs

(cherry picked from commit bda72894bb5ddc766cda0a4eda376a4a262c3845)
---
 .../ExpressionParser/Clang/ClangModulesDeclVendor.h       | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
index d820552a29129..98797e9e120bb 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
@@ -42,11 +42,11 @@ class ClangModulesDeclVendor : public ClangDeclVendor {
   ///     The path to the exact module to be loaded.  E.g., if the desired
   ///     module is std.io, then this should be { "std", "io" }.
   ///
-  /// \param[in] exported_modules
+  /// \param[out] exported_modules
   ///     If non-NULL, a pointer to a vector to populate with the ID of every
   ///     module that is re-exported by the specified module.
   ///
-  /// \param[in] error_stream
+  /// \param[out] error_stream
   ///     A stream to populate with the output of the Clang parser when
   ///     it tries to load the module.
   ///
@@ -64,11 +64,11 @@ class ClangModulesDeclVendor : public ClangDeclVendor {
   /// \param[in] cu
   ///     The compilation unit to scan for imported modules.
   ///
-  /// \param[in] exported_modules
+  /// \param[out] exported_modules
   ///     A vector to populate with the ID of each module loaded (directly
   ///     and via re-exports) in this way.
   ///
-  /// \param[in] error_stream
+  /// \param[out] error_stream
   ///     A stream to populate with the output of the Clang parser when
   ///     it tries to load the modules.
   ///

From a8d41d4f4c5f0aaf3aaf28d92d1e6f2ff3275eed Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12@gmail.com>
Date: Fri, 7 Nov 2025 22:48:48 +0000
Subject: [PATCH 2/4] [lldb][ClangModulesDeclVendor] Revamp error handling when
 loading Clang modules (#166917)

Instead of propagating the errors as a `bool`+`Stream` we change the
`ClangModulesDeclVendor` module loading APIs to use `llvm::Error`. We
also reword some of the diagnostics (notably removing the hardcoded
`error:` prefix). A follow-up patch will further make the module loading
errors less noisy.

See the new tests for what the errors look like.

rdar://164002569
(cherry picked from commit 7f55f264ec04959d4a6ec6b088d4bea0a0ff0dca)
---
 .../Clang/ClangExpressionParser.cpp           |   8 +-
 .../Clang/ClangExpressionSourceCode.cpp       |   9 +-
 .../Clang/ClangModulesDeclVendor.cpp          | 102 ++++++++++--------
 .../Clang/ClangModulesDeclVendor.h            |  18 +---
 .../Clang/ClangUserExpression.cpp             |  22 ++--
 ...stClangModuleLoadError_FromExpression.test |  54 ++++++++++
 ...oduleLoadError_InvalidNestedSubmodule.test |  59 ++++++++++
 ...langModuleLoadError_InvalidSearchPath.test |  47 ++++++++
 ...ClangModuleLoadError_InvalidSubmodule.test |  51 +++++++++
 ...ModuleLoadError_InvalidTopLevelModule.test |  48 +++++++++
 ...ClangModuleLoadError_ModulemapParsing.test |  46 ++++++++
 .../TestClangModuleLoadError_NoModule.test    |  47 ++++++++
 .../TestClangModuleLoadError_NoModuleMap.test |  42 ++++++++
 13 files changed, 471 insertions(+), 82 deletions(-)
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_FromExpression.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
index c75464d2fa1ad..edb01e0dbc8ef 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
@@ -115,6 +115,7 @@ class ClangExpressionParser::LLDBPreprocessorCallbacks : public PPCallbacks {
   ClangModulesDeclVendor &m_decl_vendor;
   ClangPersistentVariables &m_persistent_vars;
   clang::SourceManager &m_source_mgr;
+  /// Accumulates error messages across all moduleImport calls.
   StreamString m_error_stream;
   bool m_has_errors = false;
 
@@ -140,11 +141,12 @@ class ClangExpressionParser::LLDBPreprocessorCallbacks : public PPCallbacks {
       module.path.push_back(
           ConstString(component.getIdentifierInfo()->getName()));
 
-    StreamString error_stream;
-
     ClangModulesDeclVendor::ModuleVector exported_modules;
-    if (!m_decl_vendor.AddModule(module, &exported_modules, m_error_stream))
+    if (auto err = m_decl_vendor.AddModule(module, &exported_modules)) {
       m_has_errors = true;
+      m_error_stream.PutCString(llvm::toString(std::move(err)));
+      m_error_stream.PutChar('\n');
+    }
 
     for (ClangModulesDeclVendor::ModuleID module : exported_modules)
       m_persistent_vars.AddHandLoadedClangModule(module);
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
index ff9ed9c27f70f..b4e81aa21c138 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
@@ -383,10 +383,11 @@ bool ClangExpressionSourceCode::GetText(
             block->CalculateSymbolContext(&sc);
 
             if (sc.comp_unit) {
-              StreamString error_stream;
-
-              decl_vendor->AddModulesForCompileUnit(
-                  *sc.comp_unit, modules_for_macros, error_stream);
+              if (auto err = decl_vendor->AddModulesForCompileUnit(
+                      *sc.comp_unit, modules_for_macros))
+                LLDB_LOG_ERROR(
+                    GetLog(LLDBLog::Expressions), std::move(err),
+                    "Error while loading hand-imported modules: {0}");
             }
           }
         }
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
index d421d6d8067b4..0fe14cd816ea2 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
@@ -92,11 +92,11 @@ class ClangModulesDeclVendorImpl : public ClangModulesDeclVendor {
 
   ~ClangModulesDeclVendorImpl() override = default;
 
-  bool AddModule(const SourceModule &module, ModuleVector *exported_modules,
-                 Stream &error_stream) override;
+  llvm::Error AddModule(const SourceModule &module,
+                        ModuleVector *exported_modules) override;
 
-  bool AddModulesForCompileUnit(CompileUnit &cu, ModuleVector &exported_modules,
-                                Stream &error_stream) override;
+  llvm::Error AddModulesForCompileUnit(CompileUnit &cu,
+                                       ModuleVector &exported_modules) override;
 
   uint32_t FindDecls(ConstString name, bool append, uint32_t max_matches,
                      std::vector<CompilerDecl> &decls) override;
@@ -273,16 +273,14 @@ void ClangModulesDeclVendorImpl::ReportModuleExports(
     exports.push_back(module);
 }
 
-bool ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
-                                           ModuleVector *exported_modules,
-                                           Stream &error_stream) {
+llvm::Error
+ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
+                                      ModuleVector *exported_modules) {
   // Fail early.
 
-  if (m_compiler_instance->hadModuleLoaderFatalFailure()) {
-    error_stream.PutCString("error: Couldn't load a module because the module "
-                            "loader is in a fatal state.\n");
-    return false;
-  }
+  if (m_compiler_instance->hadModuleLoaderFatalFailure())
+    return llvm::createStringError(
+        "couldn't load a module because the module loader is in a fatal state");
 
   // Check if we've already imported this module.
 
@@ -297,7 +295,7 @@ bool ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
     if (mi != m_imported_modules.end()) {
       if (exported_modules)
         ReportModuleExports(*exported_modules, mi->second);
-      return true;
+      return llvm::Error::success();
     }
   }
 
@@ -315,30 +313,30 @@ bool ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
                             std::equal(sysroot_begin, sysroot_end, path_begin);
     // No need to inject search paths to modules in the sysroot.
     if (!is_system_module) {
-      auto error = [&]() {
-        error_stream.Printf("error: No module map file in %s\n",
-                            module.search_path.AsCString());
-        return false;
-      };
-
       bool is_system = true;
       bool is_framework = false;
       auto dir = HS.getFileMgr().getOptionalDirectoryRef(
           module.search_path.GetStringRef());
       if (!dir)
-        return error();
+        return llvm::createStringError(
+            "couldn't find module search path directory %s",
+            module.search_path.GetCString());
+
       auto file = HS.lookupModuleMapFile(*dir, is_framework);
       if (!file)
-        return error();
+        return llvm::createStringError("couldn't find modulemap file in %s",
+                                       module.search_path.GetCString());
+
       if (HS.loadModuleMapFile(*file, is_system))
-        return error();
+        return llvm::createStringError(
+            "failed to parse and load modulemap file in %s",
+            module.search_path.GetCString());
     }
   }
-  if (!HS.lookupModule(module.path.front().GetStringRef())) {
-    error_stream.Printf("error: Header search couldn't locate module '%s'\n",
-                        module.path.front().AsCString());
-    return false;
-  }
+
+  if (!HS.lookupModule(module.path.front().GetStringRef()))
+    return llvm::createStringError("header search couldn't locate module '%s'",
+                                   module.path.front().AsCString());
 
   llvm::SmallVector<clang::IdentifierLoc, 4> clang_path;
 
@@ -364,22 +362,29 @@ bool ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
   clang::Module *top_level_module = DoGetModule(clang_path.front(), false);
 
   if (!top_level_module) {
+    lldb_private::StreamString error_stream;
     diagnostic_consumer->DumpDiagnostics(error_stream);
-    error_stream.Printf("error: Couldn't load top-level module %s\n",
-                        module.path.front().AsCString());
-    return false;
+
+    return llvm::createStringError(llvm::formatv(
+        "couldn't load top-level module {0}:\n{1}",
+        module.path.front().GetStringRef(), error_stream.GetString()));
   }
 
   clang::Module *submodule = top_level_module;
 
   for (auto &component : llvm::ArrayRef<ConstString>(module.path).drop_front()) {
-    submodule = submodule->findSubmodule(component.GetStringRef());
-    if (!submodule) {
+    clang::Module *found = submodule->findSubmodule(component.GetStringRef());
+    if (!found) {
+      lldb_private::StreamString error_stream;
       diagnostic_consumer->DumpDiagnostics(error_stream);
-      error_stream.Printf("error: Couldn't load submodule %s\n",
-                          component.GetCString());
-      return false;
+
+      return llvm::createStringError(llvm::formatv(
+          "couldn't load submodule '{0}' of module '{1}':\n{2}",
+          component.GetStringRef(), submodule->getFullModuleName(),
+          error_stream.GetString()));
     }
+
+    submodule = found;
   }
 
   // If we didn't make the submodule visible here, Clang wouldn't allow LLDB to
@@ -399,10 +404,12 @@ bool ClangModulesDeclVendorImpl::AddModule(const SourceModule &module,
 
     m_enabled = true;
 
-    return true;
+    return llvm::Error::success();
   }
 
-  return false;
+  return llvm::createStringError(
+      llvm::formatv("unknown error while loading module {0}\n",
+                    module.path.front().GetStringRef()));
 }
 
 bool ClangModulesDeclVendor::LanguageSupportsClangModules(
@@ -424,15 +431,18 @@ bool ClangModulesDeclVendor::LanguageSupportsClangModules(
   }
 }
 
-bool ClangModulesDeclVendorImpl::AddModulesForCompileUnit(
-    CompileUnit &cu, ClangModulesDeclVendor::ModuleVector &exported_modules,
-    Stream &error_stream) {
-  if (LanguageSupportsClangModules(cu.GetLanguage())) {
-    for (auto &imported_module : cu.GetImportedModules())
-      if (!AddModule(imported_module, &exported_modules, error_stream))
-        return false;
-  }
-  return true;
+llvm::Error ClangModulesDeclVendorImpl::AddModulesForCompileUnit(
+    CompileUnit &cu, ClangModulesDeclVendor::ModuleVector &exported_modules) {
+  if (!LanguageSupportsClangModules(cu.GetLanguage()))
+    return llvm::Error::success();
+
+  for (auto &imported_module : cu.GetImportedModules())
+    // TODO: don't short-circuit. Continue loading modules even if one of them
+    // fails. Concatenate all the errors.
+    if (auto err = AddModule(imported_module, &exported_modules))
+      return err;
+
+  return llvm::Error::success();
 }
 
 // ClangImporter::lookupValue
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
index 98797e9e120bb..9a85d7d326c6c 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h
@@ -46,17 +46,12 @@ class ClangModulesDeclVendor : public ClangDeclVendor {
   ///     If non-NULL, a pointer to a vector to populate with the ID of every
   ///     module that is re-exported by the specified module.
   ///
-  /// \param[out] error_stream
-  ///     A stream to populate with the output of the Clang parser when
-  ///     it tries to load the module.
-  ///
   /// \return
   ///     True if the module could be loaded; false if not.  If the
   ///     compiler encountered a fatal error during a previous module
   ///     load, then this will always return false for this ModuleImporter.
-  virtual bool AddModule(const SourceModule &module,
-                         ModuleVector *exported_modules,
-                         Stream &error_stream) = 0;
+  virtual llvm::Error AddModule(const SourceModule &module,
+                                ModuleVector *exported_modules) = 0;
 
   /// Add all modules referred to in a given compilation unit to the list
   /// of modules to search.
@@ -68,18 +63,13 @@ class ClangModulesDeclVendor : public ClangDeclVendor {
   ///     A vector to populate with the ID of each module loaded (directly
   ///     and via re-exports) in this way.
   ///
-  /// \param[out] error_stream
-  ///     A stream to populate with the output of the Clang parser when
-  ///     it tries to load the modules.
-  ///
   /// \return
   ///     True if all modules referred to by the compilation unit could be
   ///     loaded; false if one could not be loaded.  If the compiler
   ///     encountered a fatal error during a previous module
   ///     load, then this will always return false for this ModuleImporter.
-  virtual bool AddModulesForCompileUnit(CompileUnit &cu,
-                                        ModuleVector &exported_modules,
-                                        Stream &error_stream) = 0;
+  virtual llvm::Error
+  AddModulesForCompileUnit(CompileUnit &cu, ModuleVector &exported_modules) = 0;
 
   /// Enumerate all the macros that are defined by a given set of modules
   /// that are already imported.
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
index e8d5ec3c7fd96..13d32b3bbc4f3 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
@@ -371,26 +371,18 @@ static void SetupDeclVendor(ExecutionContext &exe_ctx, Target *target,
 
   if (!sc.comp_unit)
     return;
-  StreamString error_stream;
-
   ClangModulesDeclVendor::ModuleVector modules_for_macros =
       persistent_state->GetHandLoadedClangModules();
-  if (decl_vendor->AddModulesForCompileUnit(*sc.comp_unit, modules_for_macros,
-                                            error_stream))
-    return;
 
-  // Failed to load some modules, so emit the error stream as a diagnostic.
-  if (!error_stream.Empty()) {
-    // The error stream already contains several Clang diagnostics that might
-    // be either errors or warnings, so just print them all as one remark
-    // diagnostic to prevent that the message starts with "error: error:".
-    diagnostic_manager.PutString(lldb::eSeverityInfo, error_stream.GetString());
+  auto err =
+      decl_vendor->AddModulesForCompileUnit(*sc.comp_unit, modules_for_macros);
+  if (!err)
     return;
-  }
 
-  diagnostic_manager.PutString(lldb::eSeverityError,
-                               "Unknown error while loading modules needed for "
-                               "current compilation unit.");
+  // FIXME: should we be dumping these to the error log instead of as
+  // diagnostics? They are non-fatal and are usually quite noisy.
+  diagnostic_manager.PutString(lldb::eSeverityInfo,
+                               llvm::toString(std::move(err)));
 }
 
 ClangExpressionSourceCode::WrapKind ClangUserExpression::GetWrapKind() const {
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_FromExpression.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_FromExpression.test
new file mode 100644
index 0000000000000..b964e9b27e914
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_FromExpression.test
@@ -0,0 +1,54 @@
+## Tests the case where we fail to import modules from @import
+## statements that are part of the expression being run.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+#
+# RUN: sed -i '' -e 's/foo\.h/baz\.h/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr @import Foo; @import Bar
+expr @import foo
+
+# CHECK: error: while importing modules:
+# CHECK-NEXT: header search couldn't locate module 'Foo'
+# CHECK-NEXT: header search couldn't locate module 'Bar'
+#
+# CHECK: expr @import foo
+# CHECK: error: while importing modules:
+# CHECK-NEXT: couldn't load top-level module foo
+## No mention of the previous import errors.
+# CHECK-NOT: Foo
+# CHECK-NOT: Bar
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
new file mode 100644
index 0000000000000..a5822ae4a75e7
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
@@ -0,0 +1,59 @@
+## Tests the case where we fail to load a submodule of a submodule. We force this
+## by removing the submodule 'module qux' of 'module baz' from the modulemap.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: sed -i '' -e 's/module qux/module quz/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo.baz.qux;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- baz.h
+struct baz {};
+
+#--- qux.h
+struct qux {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+
+    module baz {
+        header "baz.h"
+        export *
+
+        module qux {
+            header "qux.h"
+            export *
+        }
+    }
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: couldn't load submodule 'qux' of module 'foo.baz'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
new file mode 100644
index 0000000000000..0fda05283608e
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
@@ -0,0 +1,47 @@
+## Tests the case where the DW_AT_LLVM_include_path of the module is invalid.
+## We forces this by just removing that directory (which in our case is 'sources').
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+#
+# RUN: cp %t/sources/commands.input %t/commands.input
+# RUN: rm -r %t/sources
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: couldn't find module search path directory {{.*}}sources
+## FIXME: We never attempted to load bar.
+# CHECK-NOT: couldn't find module search path
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
new file mode 100644
index 0000000000000..2552cdb4b61db
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
@@ -0,0 +1,51 @@
+## Tests the case where we fail to load a submodule. We force this by removing
+## the submodule 'module baz' from the modulemap.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: sed -i '' -e 's/module baz/module qux/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo.baz;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- baz.h
+struct baz {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+
+    module baz {
+        header "baz.h"
+        export *
+    }
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: couldn't load submodule 'baz' of module 'foo'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
new file mode 100644
index 0000000000000..a50f784dd1dc2
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
@@ -0,0 +1,48 @@
+## Tests the case where a module fails to load. We force this by
+## replacing the contents of the 'module foo' declaration with garbage.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: sed -i '' -e 's/foo\.h/baz\.h/' %t/sources/module.modulemap
+# RUN: sed -i '' -e 's/bar\.h/qux\.h/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: couldn't load top-level module foo
+## FIXME: clang error diagnostic shouldn't be dumped to the console.
+# CHECK: error:
+## FIXME: We never attempted to load bar.
+# CHECK-NOT: bar
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
new file mode 100644
index 0000000000000..cadeb2de02c87
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
@@ -0,0 +1,46 @@
+## Tests the case where the modulemap is semantically invalid and thus
+## Clang fails to load it on behalf of LLDB. We force this error by
+## creating a redefinition of 'module bar'.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: sed -i '' -e 's/module foo/module bar/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: failed to parse and load modulemap file in {{.*}}sources
+## FIXME: We never attempted to load bar.
+# CHECK-NOT: failed to parse and load modulemap
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
new file mode 100644
index 0000000000000..a14f51eeba073
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
@@ -0,0 +1,47 @@
+## Tests the case where the module LLDB is trying to load isn't
+## present in the modulemap. We force this by replacing 'module foo'
+## in the modulemap.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: sed -i '' -e 's/module foo/module baz/' %t/sources/module.modulemap
+# RUN: sed -i '' -e 's/module bar/module qux/' %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: header search couldn't locate module 'foo'
+## FIXME: We never attempted to load bar.
+# CHECK-NOT: bar
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
new file mode 100644
index 0000000000000..a4fcace4f5b51
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
@@ -0,0 +1,42 @@
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+# RUN: rm %t/sources/module.modulemap
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+@import bar;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#--- bar.h
+struct bar {};
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+module bar {
+    header "bar.h"
+    export *
+}
+
+#--- commands.input
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: note: couldn't find modulemap file in {{.*}}sources
+## FIXME: We never attempted to load bar.
+# CHECK-NOT: couldn't find modulemap

From 59fbfa8222e72dfdfea93d5cbcde2a2949b3137d Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12@gmail.com>
Date: Fri, 7 Nov 2025 23:11:48 +0000
Subject: [PATCH 3/4] [lldb][ClangModulesDeclVendor] Don't stop loading Clang
 modules if an individual import failed (#166940)

Depends on:
* https://github.com/llvm/llvm-project/pull/166917

When loading all Clang modules for a CU, we stop on first error. This
means benign module loading errors may stop us from importing actually
useful modules. There's no good reason to bail on the first one. The
pathological case would be if we try to load a large number of Clang
modules
but all fail to load for the same reason. That could happen, but in
practice I've always seen only a handful of modules failing to load out
of a large number. Particularly system modules are useful and usually
don't fail to load. Whereas project-specific Clang modules are more
likely to fail because the build system moves the modulemap/sources
around.

This patch accumulates all module loading errors and doesn't stop when
an error is encountered.

(cherry picked from commit 74e34eff3febe89b03acb956af5baf5b089cd121)
---
 .../ExpressionParser/Clang/ClangExpressionSourceCode.cpp  | 2 +-
 .../ExpressionParser/Clang/ClangModulesDeclVendor.cpp     | 8 ++++----
 .../ExpressionParser/Clang/ClangUserExpression.cpp        | 6 ++++--
 .../Expr/TestClangModuleLoadError_InvalidSearchPath.test  | 3 +--
 .../TestClangModuleLoadError_InvalidTopLevelModule.test   | 5 +++--
 .../Expr/TestClangModuleLoadError_ModulemapParsing.test   | 3 +--
 .../Shell/Expr/TestClangModuleLoadError_NoModule.test     | 3 +--
 .../Shell/Expr/TestClangModuleLoadError_NoModuleMap.test  | 3 +--
 8 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
index b4e81aa21c138..ad48d293ab8f0 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
@@ -387,7 +387,7 @@ bool ClangExpressionSourceCode::GetText(
                       *sc.comp_unit, modules_for_macros))
                 LLDB_LOG_ERROR(
                     GetLog(LLDBLog::Expressions), std::move(err),
-                    "Error while loading hand-imported modules: {0}");
+                    "Error while loading hand-imported modules:\n{0}");
             }
           }
         }
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
index 0fe14cd816ea2..65709180b3287 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
@@ -436,13 +436,13 @@ llvm::Error ClangModulesDeclVendorImpl::AddModulesForCompileUnit(
   if (!LanguageSupportsClangModules(cu.GetLanguage()))
     return llvm::Error::success();
 
+  llvm::Error errors = llvm::Error::success();
+
   for (auto &imported_module : cu.GetImportedModules())
-    // TODO: don't short-circuit. Continue loading modules even if one of them
-    // fails. Concatenate all the errors.
     if (auto err = AddModule(imported_module, &exported_modules))
-      return err;
+      errors = llvm::joinErrors(std::move(errors), std::move(err));
 
-  return llvm::Error::success();
+  return errors;
 }
 
 // ClangImporter::lookupValue
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
index 13d32b3bbc4f3..9a5d49a7ea363 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
@@ -381,8 +381,10 @@ static void SetupDeclVendor(ExecutionContext &exe_ctx, Target *target,
 
   // FIXME: should we be dumping these to the error log instead of as
   // diagnostics? They are non-fatal and are usually quite noisy.
-  diagnostic_manager.PutString(lldb::eSeverityInfo,
-                               llvm::toString(std::move(err)));
+  llvm::handleAllErrors(
+      std::move(err), [&diagnostic_manager](const llvm::StringError &e) {
+        diagnostic_manager.PutString(lldb::eSeverityInfo, e.getMessage());
+      });
 }
 
 ClangExpressionSourceCode::WrapKind ClangUserExpression::GetWrapKind() const {
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
index 0fda05283608e..e5a6334d2ee22 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
@@ -43,5 +43,4 @@ run
 expr blah
 
 # CHECK: note: couldn't find module search path directory {{.*}}sources
-## FIXME: We never attempted to load bar.
-# CHECK-NOT: couldn't find module search path
+# CHECK: note: couldn't find module search path directory {{.*}}sources
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
index a50f784dd1dc2..189a3c0fcdf26 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
@@ -44,5 +44,6 @@ expr blah
 # CHECK: note: couldn't load top-level module foo
 ## FIXME: clang error diagnostic shouldn't be dumped to the console.
 # CHECK: error:
-## FIXME: We never attempted to load bar.
-# CHECK-NOT: bar
+# CHECK: note: couldn't load top-level module bar
+## FIXME: clang error diagnostic shouldn't be dumped to the console.
+# CHECK: error:
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
index cadeb2de02c87..53efffffe435c 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
@@ -42,5 +42,4 @@ run
 expr blah
 
 # CHECK: note: failed to parse and load modulemap file in {{.*}}sources
-## FIXME: We never attempted to load bar.
-# CHECK-NOT: failed to parse and load modulemap
+# CHECK: note: failed to parse and load modulemap file in {{.*}}sources
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
index a14f51eeba073..2962614086931 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
@@ -43,5 +43,4 @@ run
 expr blah
 
 # CHECK: note: header search couldn't locate module 'foo'
-## FIXME: We never attempted to load bar.
-# CHECK-NOT: bar
+# CHECK: note: header search couldn't locate module 'bar'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
index a4fcace4f5b51..917facb05fd47 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
@@ -38,5 +38,4 @@ run
 expr blah
 
 # CHECK: note: couldn't find modulemap file in {{.*}}sources
-## FIXME: We never attempted to load bar.
-# CHECK-NOT: couldn't find modulemap
+# CHECK: note: couldn't find modulemap file in {{.*}}sources

From e35b62825b648db6221781d5e106d9d95bc95f84 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12@gmail.com>
Date: Sat, 8 Nov 2025 00:21:03 +0000
Subject: [PATCH 4/4] [lldb][ClangModulesDeclVendor] Print Clang module loading
 errors to expression log instead of console (#166964)

Depends on:
* https://github.com/llvm/llvm-project/pull/166917
* https://github.com/llvm/llvm-project/pull/166940

While these errors can contribute to an expression failing, they are
never *the* reason the expression failed. I.e., they are always just
'note:' diagnostics that we hand-emit. Because they are quite noisy (and
we potentially have many of them if we auto-load all modules in a CU),
this patch logs the errors to the `expr` log, instead of the console.

Previously these errors would only get omitted when the expression
itself failed. Meaning if the expression failed, we'd dump these 'note'
module load errors in next to the actual expression error, obscuring the
output. Moreover, if the expression succeeded, any module load errors
would be dropped. Now we always log all module loading errors to the
expression log, regardless of whether the expression fails or not.

(cherry picked from commit d5b62fabd17ee14805f4c5c5ac7b0be9bf488211)
---
 .../Clang/ClangUserExpression.cpp             | 12 ++---
 .../lang/objc/modules-compile-error/Makefile  |  5 --
 .../TestModulesCompileError.py                | 28 -----------
 .../lang/objc/modules-compile-error/main.m    |  5 --
 .../lang/objc/modules-compile-error/module.h  |  5 --
 .../modules-compile-error/module.modulemap    |  1 -
 ...stClangModuleLoadError_CompileFailure.test | 46 +++++++++++++++++++
 ...oduleLoadError_InvalidNestedSubmodule.test | 15 +++++-
 ...langModuleLoadError_InvalidSearchPath.test | 19 ++++++--
 ...ClangModuleLoadError_InvalidSubmodule.test | 15 +++++-
 ...ModuleLoadError_InvalidTopLevelModule.test | 24 +++++++---
 ...ClangModuleLoadError_ModulemapParsing.test | 18 ++++++--
 .../TestClangModuleLoadError_NoModule.test    | 18 ++++++--
 .../TestClangModuleLoadError_NoModuleMap.test | 18 ++++++--
 14 files changed, 156 insertions(+), 73 deletions(-)
 delete mode 100644 lldb/test/API/lang/objc/modules-compile-error/Makefile
 delete mode 100644 lldb/test/API/lang/objc/modules-compile-error/TestModulesCompileError.py
 delete mode 100644 lldb/test/API/lang/objc/modules-compile-error/main.m
 delete mode 100644 lldb/test/API/lang/objc/modules-compile-error/module.h
 delete mode 100644 lldb/test/API/lang/objc/modules-compile-error/module.modulemap
 create mode 100644 lldb/test/Shell/Expr/TestClangModuleLoadError_CompileFailure.test

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
index 9a5d49a7ea363..d1feda1f0b629 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
@@ -379,12 +379,12 @@ static void SetupDeclVendor(ExecutionContext &exe_ctx, Target *target,
   if (!err)
     return;
 
-  // FIXME: should we be dumping these to the error log instead of as
-  // diagnostics? They are non-fatal and are usually quite noisy.
-  llvm::handleAllErrors(
-      std::move(err), [&diagnostic_manager](const llvm::StringError &e) {
-        diagnostic_manager.PutString(lldb::eSeverityInfo, e.getMessage());
-      });
+  // Module load errors aren't fatal to the expression evaluator. Printing
+  // them as diagnostics to the console would be too noisy and misleading
+  // Hence just print them to the expression log.
+  llvm::handleAllErrors(std::move(err), [](const llvm::StringError &e) {
+    LLDB_LOG(GetLog(LLDBLog::Expressions), "{0}", e.getMessage());
+  });
 }
 
 ClangExpressionSourceCode::WrapKind ClangUserExpression::GetWrapKind() const {
diff --git a/lldb/test/API/lang/objc/modules-compile-error/Makefile b/lldb/test/API/lang/objc/modules-compile-error/Makefile
deleted file mode 100644
index e031aa0bbbb8d..0000000000000
--- a/lldb/test/API/lang/objc/modules-compile-error/Makefile
+++ /dev/null
@@ -1,5 +0,0 @@
-OBJC_SOURCES := main.m
-
-CFLAGS_EXTRAS = $(MANDATORY_MODULE_BUILD_CFLAGS) -I$(BUILDDIR) -DONLY_CLANG=1
-
-include Makefile.rules
diff --git a/lldb/test/API/lang/objc/modules-compile-error/TestModulesCompileError.py b/lldb/test/API/lang/objc/modules-compile-error/TestModulesCompileError.py
deleted file mode 100644
index db6d74bfdb540..0000000000000
--- a/lldb/test/API/lang/objc/modules-compile-error/TestModulesCompileError.py
+++ /dev/null
@@ -1,28 +0,0 @@
-import lldb
-from lldbsuite.test.decorators import *
-from lldbsuite.test.lldbtest import *
-from lldbsuite.test import lldbutil
-
-
-class TestCase(TestBase):
-    @skipIf(compiler="clang", compiler_version=["<", "11.0"])
-    def test(self):
-        self.build()
-        lldbutil.run_to_source_breakpoint(
-            self, "// break here", lldb.SBFileSpec("main.m")
-        )
-
-        # Try importing our custom module. This will fail as LLDB won't define
-        # the CLANG_ONLY define when it compiles the module for the expression
-        # evaluator.
-        # Check that the error message shows file/line/column, prints the relevant
-        # line from the source code and mentions the module that failed to build.
-        self.expect(
-            "expr @import LLDBTestModule",
-            error=True,
-            substrs=[
-                "module.h:4:1: error: unknown type name 'syntax_error_for_lldb_to_find'",
-                "syntax_error_for_lldb_to_find // comment that tests source printing",
-                "could not build module 'LLDBTestModule'",
-            ],
-        )
diff --git a/lldb/test/API/lang/objc/modules-compile-error/main.m b/lldb/test/API/lang/objc/modules-compile-error/main.m
deleted file mode 100644
index 35259dd287b01..0000000000000
--- a/lldb/test/API/lang/objc/modules-compile-error/main.m
+++ /dev/null
@@ -1,5 +0,0 @@
-@import LLDBTestModule;
-
-int main() {
-  return foo(); // break here
-}
diff --git a/lldb/test/API/lang/objc/modules-compile-error/module.h b/lldb/test/API/lang/objc/modules-compile-error/module.h
deleted file mode 100644
index 2edd13b0832db..0000000000000
--- a/lldb/test/API/lang/objc/modules-compile-error/module.h
+++ /dev/null
@@ -1,5 +0,0 @@
-int foo() { return 123; }
-
-#ifndef ONLY_CLANG
-syntax_error_for_lldb_to_find // comment that tests source printing
-#endif
diff --git a/lldb/test/API/lang/objc/modules-compile-error/module.modulemap b/lldb/test/API/lang/objc/modules-compile-error/module.modulemap
deleted file mode 100644
index 3d44faf3e9080..0000000000000
--- a/lldb/test/API/lang/objc/modules-compile-error/module.modulemap
+++ /dev/null
@@ -1 +0,0 @@
-module LLDBTestModule { header "module.h" export * }
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_CompileFailure.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_CompileFailure.test
new file mode 100644
index 0000000000000..49ee2778ea18b
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_CompileFailure.test
@@ -0,0 +1,46 @@
+## Tests the case where module compilation fails.
+#
+# REQUIRES: system-darwin
+#
+# RUN: split-file %s %t/sources
+# RUN: %clang_host -g %t/sources/main.m -fmodules -fcxx-modules \
+# RUN:             -DSHOULD_COMPILE=1 \
+# RUN:             -fmodule-map-file=%t/sources/module.modulemap \
+# RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+
+#--- main.m
+@import foo;
+
+int main() { __builtin_debugtrap(); }
+
+#--- foo.h
+struct foo {};
+
+#ifndef SHOULD_COMPILE
+#error "Compilation failure."
+#endif
+
+#--- module.modulemap
+module foo {
+    header "foo.h"
+    export *
+}
+
+#--- commands.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# CHECK: Finished building Clang module foo
+# CHECK: couldn't load top-level module foo:
+# CHECK: While building module 'foo' imported from LLDBModulesMemoryBuffer
+# CHEKC: {{.*}}sources/foo.h{{.*}}: error: "Compilation failure."
+# CHECK: LLDBModulesMemoryBuffer:1:1: fatal error: could not build module 'foo'
+
+# CHECK: Error while loading hand-imported modules:
+# CHECK: couldn't load top-level module foo:
+# CHECK-NOT: Compilation failure
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
index a5822ae4a75e7..1e8075dd20fad 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidNestedSubmodule.test
@@ -10,7 +10,10 @@
 # RUN: sed -i '' -e 's/module qux/module quz/' %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo.baz.qux;
@@ -56,4 +59,12 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: couldn't load submodule 'qux' of module 'foo.baz'
+# NO_LOG-NOT: couldn't load submodule 'qux' of module 'foo.baz'
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: couldn't load submodule 'qux' of module 'foo.baz'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
index e5a6334d2ee22..35ba5802d2add 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSearchPath.test
@@ -9,10 +9,14 @@
 # RUN:             -fmodules-cache-path=%t/ModuleCache -o %t.out
 #
 # RUN: cp %t/sources/commands.input %t/commands.input
+# RUN: cp %t/sources/commands-with-log.input %t/commands-with-log.input
 # RUN: rm -r %t/sources
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo;
@@ -42,5 +46,14 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: couldn't find module search path directory {{.*}}sources
-# CHECK: note: couldn't find module search path directory {{.*}}sources
+# NO_LOG-NOT: couldn't find module search path directory {{.*}}sources
+# NO_LOG-NOT: couldn't find module search path directory {{.*}}sources
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: couldn't find module search path directory {{.*}}sources
+# LOG: couldn't find module search path directory {{.*}}sources
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
index 2552cdb4b61db..1bfbbcf32ecae 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidSubmodule.test
@@ -10,7 +10,10 @@
 # RUN: sed -i '' -e 's/module baz/module qux/' %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo.baz;
@@ -48,4 +51,12 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: couldn't load submodule 'baz' of module 'foo'
+# NO_LOG-NOT: couldn't load submodule 'baz' of module 'foo'
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: couldn't load submodule 'baz' of module 'foo'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
index 189a3c0fcdf26..ad181ee7e15e6 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_InvalidTopLevelModule.test
@@ -11,7 +11,10 @@
 # RUN: sed -i '' -e 's/bar\.h/qux\.h/' %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo;
@@ -41,9 +44,16 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: couldn't load top-level module foo
-## FIXME: clang error diagnostic shouldn't be dumped to the console.
-# CHECK: error:
-# CHECK: note: couldn't load top-level module bar
-## FIXME: clang error diagnostic shouldn't be dumped to the console.
-# CHECK: error:
+# NO_LOG-NOT: couldn't load top-level module foo
+# NO_LOG-NOT: error: header
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: couldn't load top-level module foo
+# LOG: error: header 'baz.h'
+# LOG: couldn't load top-level module bar
+# LOG: error: header 'qux.h'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
index 53efffffe435c..6d8e665102b17 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_ModulemapParsing.test
@@ -11,7 +11,10 @@
 # RUN: sed -i '' -e 's/module foo/module bar/' %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo;
@@ -41,5 +44,14 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: failed to parse and load modulemap file in {{.*}}sources
-# CHECK: note: failed to parse and load modulemap file in {{.*}}sources
+# NO_LOG-NOT: failed to parse and load
+# NO_LOG-NOT: failed to parse and load
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: failed to parse and load modulemap file in {{.*}}sources
+# LOG: failed to parse and load modulemap file in {{.*}}sources
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
index 2962614086931..bcb8a7d2c5594 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModule.test
@@ -12,7 +12,10 @@
 # RUN: sed -i '' -e 's/module bar/module qux/' %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo;
@@ -42,5 +45,14 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: header search couldn't locate module 'foo'
-# CHECK: note: header search couldn't locate module 'bar'
+# NO_LOG-NOT: header search couldn't locate module 'foo'
+# NO_LOG-NOT: header search couldn't locate module 'bar'
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: header search couldn't locate module 'foo'
+# LOG: header search couldn't locate module 'bar'
diff --git a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
index 917facb05fd47..57f7f16cc84dd 100644
--- a/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
+++ b/lldb/test/Shell/Expr/TestClangModuleLoadError_NoModuleMap.test
@@ -7,7 +7,10 @@
 # RUN: rm %t/sources/module.modulemap
 #
 # RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
-# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s
+# RUN:       -s %t/sources/commands.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=NO_LOG
+#
+# RUN: %lldb -x -o "settings set interpreter.stop-command-source-on-error false" \
+# RUN:       -s %t/sources/commands-with-log.input %t.out -o exit 2>&1 | FileCheck %s --check-prefix=LOG
 
 #--- main.m
 @import foo;
@@ -37,5 +40,14 @@ run
 ## Make sure expression fails so the 'note' diagnostics get printed.
 expr blah
 
-# CHECK: note: couldn't find modulemap file in {{.*}}sources
-# CHECK: note: couldn't find modulemap file in {{.*}}sources
+# NO_LOG-NOT: couldn't find modulemap
+# NO_LOG-NOT: couldn't find modulemap
+
+#--- commands-with-log.input
+log enable lldb expr
+run
+## Make sure expression fails so the 'note' diagnostics get printed.
+expr blah
+
+# LOG: couldn't find modulemap file in {{.*}}sources
+# LOG: couldn't find modulemap file in {{.*}}sources