Warn on multiple '-swift-module-file' options

Author: artemcm

include/swift/AST/DiagnosticsFrontend.def

@@ -211,6 +211,9 @@ ERROR(error_stdlib_module_name,none,
       "module name \"%0\" is reserved for the standard library"
       "%select{|; use -module-name flag to specify an alternate name}1",
       (StringRef, bool))
+WARNING(warn_multiple_module_inputs_same_name,none,
+        "multiple Swift module file inputs with identifier \"%0\": replacing '%1' with '%2'",
+        (StringRef, StringRef, StringRef))
 
 ERROR(error_bad_export_as_name,none,
       "export-as name \"%0\" is not a valid identifier",

lib/Frontend/CompilerInvocation.cpp

@@ -2310,7 +2310,15 @@ static bool validateSwiftModuleFileArgumentAndAdd(const std::string &swiftModule
     Diags.diagnose(SourceLoc(), diag::error_bad_module_name, moduleName, false);
     return true;
   }
-  ExplicitSwiftModuleInputs.insert(std::make_pair(moduleName, modulePath));
+
+  auto priorEntryIt = ExplicitSwiftModuleInputs.find(moduleName);
+  if (priorEntryIt != ExplicitSwiftModuleInputs.end()) {
+    Diags.diagnose(SourceLoc(), diag::warn_multiple_module_inputs_same_name,
+                   moduleName, priorEntryIt->getValue(), modulePath);
+    ExplicitSwiftModuleInputs[moduleName] = modulePath;
+  } else
+    ExplicitSwiftModuleInputs.insert(std::make_pair(moduleName, modulePath));
+
   return false;
 }
 

test/ScanDependencies/explicit-scanner-input-can-import.swift

@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/module-cache)
+// RUN: %empty-directory(%t/Inputs/Foo.swiftmodule)
+// RUN: split-file %s %t
+
+// Step 1: build swift interface and swift module side by side
+// RUN: %target-swift-frontend -emit-module %t/Foo.swift -emit-module-path %t/Inputs/Foo.swiftmodule/%target-swiftmodule-name -module-name Foo -user-module-version 22
+
+// Step 2: scan dependency should give us the binary module we specify with 'swift-module-file'
+// RUN: %target-swift-frontend -scan-dependencies %t/test.swift -o %t/deps.json -scanner-module-validation -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/%target-swiftmodule-name
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=CHECK-INPUT
+
+// Step 3: ensure that versioned canImport still applies with direct -swift-module-file
+// RUN: %target-swift-frontend -scan-dependencies %t/test_too_new.swift -o %t/deps.json -scanner-module-validation -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/%target-swiftmodule-name
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=CHECK-MISSING
+
+// CHECK-INPUT: "swiftPrebuiltExternal": "Foo"
+// CHECK-MISSING-NOT: "swiftPrebuiltExternal": "Foo"
+
+//--- Foo.swift
+public func foo() {}
+
+//--- test.swift
+#if canImport(Foo)
+import Foo
+#endif
+
+//--- test_too_new.swift
+#if canImport(Foo, _version: 23)
+import Foo
+#endif

test/ScanDependencies/explicit-scanner-input.swift

@@ -9,11 +9,18 @@
 // Step 2: scan dependency should give us the binary module we specify with 'swift-module-file'
 // RUN: %target-swift-frontend -scan-dependencies %t/test.swift -o %t/deps.json -scanner-module-validation -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/%target-swiftmodule-name
 // RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=CHECK-INPUT
-// CHECK-INPUT: "swiftPrebuiltExternal": "Foo"
 
-// Step 3: verify that the usual invalid module candidate diagnostics apply
+// Step 3: ensure that if multiple inputs for the same module are specified then a warning is emitted and the latter is preferred
+// RUN: echo "Gibberish" > %t/Inputs/Foo.swiftmodule/NotAModule.swiftmodule
+// RUN: %target-swift-frontend -scan-dependencies %t/test.swift -o %t/deps.json -scanner-module-validation -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/NotAModule.swiftmodule -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/%target-swiftmodule-name -diagnostic-style llvm 2>&1 | %FileCheck %s -check-prefix=CHECK-WARN-MULTIPLE
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=CHECK-INPUT
+
+// Step 4: verify that the usual invalid module candidate diagnostics apply
 // RUN: echo "Not Really a module" > %t/Inputs/Foo.swiftmodule/%target-swiftmodule-name
 // RUN: %target-swift-frontend -scan-dependencies %t/test.swift -o %t/deps.json  -scanner-module-validation -swift-module-file=Foo=%t/Inputs/Foo.swiftmodule/%target-swiftmodule-name -diagnostic-style llvm 2>&1 | %FileCheck %s -check-prefix=CHECK-INVALID-MODULE-DIAG
+
+// CHECK-INPUT: "swiftPrebuiltExternal": "Foo"
+// CHECK-WARN-MULTIPLE: warning: multiple Swift module file inputs with identifier "Foo": replacing '{{.*}}NotAModule.swiftmodule'
 // CHECK-INVALID-MODULE-DIAG: error: unable to resolve Swift module dependency to a compatible module: 'Foo'
 // CHECK-INVALID-MODULE-DIAG: note: found incompatible module '{{.*}}': malformed