ModuleInterfaceBuilder: give a more specific error message in case of a compiler mismatch

Author: eeckstein

include/swift/AST/DiagnosticsSema.def

@@ -728,6 +728,10 @@ ERROR(module_interface_build_failed,Fatal,
       "the textual interface may be broken by project issues"
       "%select{, differences between compilers (the producer '%3' and this compiler '%4')|}2 or a compiler bug",
       (bool, StringRef, bool, StringRef, StringRef))
+ERROR(module_interface_build_failed_mismatching_compiler,Fatal,
+      "failed to build module '%0'; this SDK is not supported by the compiler "
+      "(the SDK is built with '%1', while this compiler is '%2'). Please select a toolchain which matches the SDK.",
+      (StringRef, StringRef, StringRef))
 ERROR(serialization_malformed_module,Fatal,
       "malformed compiled module: %0", (StringRef))
 ERROR(serialization_module_too_new,Fatal,

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -203,9 +203,14 @@ bool ModuleInterfaceBuilder::buildSwiftModuleInternal(
             getSwiftInterfaceCompilerVersionForCurrentCompiler(
                 SubInstance.getASTContext());
         StringRef emittedByCompiler = info.CompilerVersion;
-        diagnose(diag::module_interface_build_failed, isTypeChecking,
-                 moduleName, emittedByCompiler == builtByCompiler,
-                 emittedByCompiler, builtByCompiler);
+        if (!isTypeChecking && emittedByCompiler != builtByCompiler) {
+          diagnose(diag::module_interface_build_failed_mismatching_compiler,
+                   moduleName, emittedByCompiler, builtByCompiler);
+        } else {
+          diagnose(diag::module_interface_build_failed, isTypeChecking,
+                   moduleName, emittedByCompiler == builtByCompiler,
+                   emittedByCompiler, builtByCompiler);
+        }
       }
     };
 

test/ModuleInterface/unbuildable.swift

@@ -29,7 +29,7 @@ import UnbuildableCurrent
 // CURRENT: unbuildable.swift:[[@LINE-1]]:8: error: failed to build module 'UnbuildableCurrent' for importation due to the errors above; the textual interface may be broken by project issues or a compiler bug
 #else
 import UnbuildableFuture
-// FUTURE: unbuildable.swift:[[@LINE-1]]:8: error: failed to build module 'UnbuildableFuture' for importation due to the errors above; the textual interface may be broken by project issues, differences between compilers (the producer 'NeoTokyoSwift 2000.42' and this compiler '{{.*Swift version.*}}') or a compiler bug
+// FUTURE: unbuildable.swift:[[@LINE-1]]:8: error: failed to build module 'UnbuildableFuture'; this SDK is not supported by the compiler (the SDK is built with 'NeoTokyoSwift 2000.42', while this compiler is '{{.*Swift version.*}}'). Please select a toolchain which matches the SDK.
 #endif
 
 // CURRENT-VERIFY: UnbuildableCurrent.swiftinterface:1:1: error: failed to verify module interface of 'UnbuildableCurrent' due to the errors above; the textual interface may be broken by project issues or a compiler bug

validation-test/ParseableInterface/failing-overlay.swift

@@ -3,4 +3,4 @@
 
 import ImportsOverlay
 
-// CHECK: HasOverlay.swiftinterface:1:1: error: failed to build module 'HasOverlay' for importation due to the errors above; the textual interface may be broken by project issues, differences between compilers (the producer '(unspecified, file possibly handwritten)' and this compiler '{{.*Swift version.*}}') or a compiler bug
+// CHECK: HasOverlay.swiftinterface:1:1: error: failed to build module 'HasOverlay'; this SDK is not supported by the compiler (the SDK is built with '(unspecified, file possibly handwritten)', while this compiler is '{{.*Swift version.*}}'). Please select a toolchain which matches the SDK.