[clang][deps] Prevent emitting diagnostics outside of source file

[jansvoboda11]

Summary

The dependency scanner needs to report the module map file describing the module whose implementation is being compiled (see D134222). However, calling Preprocessor::getCurrentModuleImplementation() in the scanner might cause a diagnostic during module map parsing and emitting a diagnostic without being "in" a source file is illegal (e.g. in TextDiagnosticPrinter). This patch ensures the module map parse is triggered while the compiler is still "in" a source file, avoiding the failure case.

[Bigcheese]

lgtm

clang/lib/Frontend/FrontendAction.cpp

bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
   for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
     if (auto File = CI.getFileManager().getFile(Filename))
       CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
           *File, /*IsSystem*/false);
     else
       CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
   }
 
+  // If compiling implementation of a module, load its module map file now.
+  (void)CI.getPreprocessor().getCurrentModuleImplementation();
+
   // Add a module declaration scope so that modules from -fmodule-map-file
   // arguments may shadow modules found implicitly in search paths.
   CI.getPreprocessor()
       .getHeaderSearchInfo()
       .getModuleMap()
       .finishModuleDeclarationScope();
 
   // Create the AST context and consumer unless this is a preprocessor only

clang/test/ClangScanDeps/modules-implementation-module-map.c

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+//--- cdb.json.template
+[{
+  "file": "DIR/tu.m",
+  "directory": "DIR",
+  "command": "clang -fmodules -fimplicit-module-maps -fmodules-cache-path=DIR/cache -fmodule-name=FWPrivate -c DIR/tu.m -o DIR/tu.o -F DIR/frameworks -Wprivate-module"
+}]
+
+//--- frameworks/FW.framework/Modules/module.modulemap
+framework module FW {}
+//--- frameworks/FW.framework/Modules/module.private.modulemap
+// The module name will trigger a diagnostic.
+framework module FWPrivate { header "private.h" }
+//--- frameworks/FW.framework/PrivateHeaders/private.h
+//--- tu.m
+
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full > %t/result.json
+// RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t
+// CHECK:      "translation-units": [
+// CHECK-NEXT:   {
+// CHECK-NEXT:     "commands": [
+// CHECK:            {
+// CHECK:              "command-line": [
+// CHECK:                "-fmodule-map-file=[[PREFIX]]/frameworks/FW.framework/Modules/module.private.modulemap",
+// CHECK:                "-fmodule-name=FWPrivate",
+// CHECK:              ],
+// CHECK-NEXT:         "executable": "clang",
+// CHECK-NEXT:         "file-deps": [
+// CHECK-NEXT:           "[[PREFIX]]/tu.m"
+// CHECK-NEXT:         ],
+// CHECK-NEXT:         "input-file": "[[PREFIX]]/tu.m"
+// CHECK-NEXT:       }
+// CHECK:          ]
+// CHECK:        }
+// CHECK:      ]