Merge pull request #73402 from cachemeifyoucan/eng/PR-127459045

[ScanDependencies] Fix assertion failure when failed to scan header

Author: cachemeifyoucan

lib/ClangImporter/ClangModuleDependencyScanner.cpp

@@ -493,11 +493,8 @@ bool ClangImporter::addHeaderDependencies(
     auto dependencies = clangScanningTool.getTranslationUnitDependencies(
         commandLineArgs, workingDir, cache.getAlreadySeenClangModules(),
         lookupModuleOutput);
-    if (!dependencies) {
-      // FIXME: Route this to a normal diagnostic.
-      llvm::logAllUnhandledErrors(dependencies.takeError(), llvm::errs());
+    if (!dependencies)
       return dependencies.takeError();
-    }
 
     // Record module dependencies for each new module we found.
     auto bridgedDeps = bridgeClangModuleDependencies(
@@ -527,8 +524,15 @@ bool ClangImporter::addHeaderDependencies(
       !targetModule.getBridgingHeader()->empty()) {
     auto clangModuleDependencies =
         scanHeaderDependencies(*targetModule.getBridgingHeader());
-    if (!clangModuleDependencies)
+    if (!clangModuleDependencies) {
+      // FIXME: Route this to a normal diagnostic.
+      llvm::logAllUnhandledErrors(clangModuleDependencies.takeError(),
+                                  llvm::errs());
+      Impl.SwiftContext.Diags.diagnose(
+          SourceLoc(), diag::clang_dependency_scan_error,
+          "failed to scan bridging header dependencies");
       return true;
+    }
     if (auto TreeID = clangModuleDependencies->IncludeTreeID)
       targetModule.addBridgingHeaderIncludeTree(*TreeID);
     recordBridgingHeaderOptions(targetModule, *clangModuleDependencies);

test/ScanDependencies/clang_scan_error.swift

@@ -0,0 +1,15 @@
+// REQUIRES: objc_interop
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/main.swift -import-objc-header %t/bridging.h \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -o %t/deps.json -I %t -swift-version 5 2>&1 | %FileCheck %s
+
+// CHECK: error: Clang dependency scanner failure: failed to scan bridging header dependencies
+
+//--- bridging.h
+#include "do-not-exist.h"
+
+//--- main.swift
+func test() {}