[clang][modules][pch] Allow loading PCH with different modules cache path

[jansvoboda11]

Summary

It's useful to be able to load explicitly-built PCH files into an implicit build (e.g. during dependency scanning). That's currently impossible, since the explicitly-built PCH has an empty modules cache path, while the current compilation has (and needs to have) a valid path, triggering an error in the PCHValidator.

This patch adds a preprocessor option and command-line flag that can be used to omit this check.

[jansvoboda11]

Mark as CC1Option

[jansvoboda11]

Remove CC1Option

[dexonsmith]

LGTM.

clang/include/clang/Driver/Options.td

def fno_validate_pch : Flag<["-"], "fno-validate-pch">,
   Normalizer<"makeFlagToValueNormalizer(DisableValidationForModuleKind::All)">;
 def fallow_pcm_with_errors : Flag<["-"], "fallow-pcm-with-compiler-errors">,
   HelpText<"Accept a PCM file that was created with compiler errors">,
   MarshallingInfoFlag<FrontendOpts<"AllowPCMWithCompilerErrors">>;
 def fallow_pch_with_errors : Flag<["-"], "fallow-pch-with-compiler-errors">,
   HelpText<"Accept a PCH file that was created with compiler errors">,
   MarshallingInfoFlag<PreprocessorOpts<"AllowPCHWithCompilerErrors">>,
   ImpliedByAnyOf<[fallow_pcm_with_errors.KeyPath]>;
+def fallow_pch_with_different_modules_cache_path :
+  Flag<["-"], "fallow-pch-with-different-modules-cache-path">,
+  HelpText<"Accept a PCH file that was created with a different modules cache path">,
+  MarshallingInfoFlag<PreprocessorOpts<"AllowPCHWithDifferentModulesCachePath">>;
 def dump_deserialized_pch_decls : Flag<["-"], "dump-deserialized-decls">,
   HelpText<"Dump declarations that are deserialized from PCH, for testing">,
   MarshallingInfoFlag<PreprocessorOpts<"DumpDeserializedPCHDecls">>;
 def error_on_deserialized_pch_decl : Separate<["-"], "error-on-deserialized-decl">,
   HelpText<"Emit error if a specific declaration is deserialized from PCH, for testing">;
 def error_on_deserialized_pch_decl_EQ : Joined<["-"], "error-on-deserialized-decl=">,
   Alias<error_on_deserialized_pch_decl>;
 def static_define : Flag<["-"], "static-define">,

clang/include/clang/Lex/PreprocessorOptions.h

public:
   /// Whether to disable most of the normal validation performed on
   /// precompiled headers and module files.
   DisableValidationForModuleKind DisablePCHOrModuleValidation =
       DisableValidationForModuleKind::None;
 
   /// When true, a PCH with compiler errors will not be rejected.
   bool AllowPCHWithCompilerErrors = false;
 
+  /// When true, a PCH with modules cache path different to the current
+  /// compilation will not be rejected.
+  bool AllowPCHWithDifferentModulesCachePath = false;
+
   /// Dump declarations that are deserialized from PCH, for testing.
   bool DumpDeserializedPCHDecls = false;
 
   /// This is a set of names for decls that we do not want to be
   /// deserialized, and we emit an error if they are; for testing purposes.
   std::set<std::string> DeserializedPCHDeclsToErrorOn;
 
   /// If non-zero, the implicit PCH include is actually a precompiled

clang/lib/Serialization/ASTReader.cpp

 /// Check the header search options deserialized from the control block
 /// against the header search options in an existing preprocessor.
 ///
 /// \param Diags If non-null, produce diagnostics for any mismatches incurred.
 static bool checkHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                      StringRef SpecificModuleCachePath,
                                      StringRef ExistingModuleCachePath,
                                      DiagnosticsEngine *Diags,
-                                     const LangOptions &LangOpts) {
+                                     const LangOptions &LangOpts,
+                                     const PreprocessorOptions &PPOpts) {
   if (LangOpts.Modules) {
-    if (SpecificModuleCachePath != ExistingModuleCachePath) {
+    if (SpecificModuleCachePath != ExistingModuleCachePath &&
+        !PPOpts.AllowPCHWithDifferentModulesCachePath) {
       if (Diags)
         Diags->Report(diag::err_pch_modulecache_mismatch)
           << SpecificModuleCachePath << ExistingModuleCachePath;
       return true;
     }
   }
 
   return false;
 }
 
 bool PCHValidator::ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                            StringRef SpecificModuleCachePath,
                                            bool Complain) {
   return checkHeaderSearchOptions(HSOpts, SpecificModuleCachePath,
                                   PP.getHeaderSearchInfo().getModuleCachePath(),
                                   Complain ? &Reader.Diags : nullptr,
-                                  PP.getLangOpts());
+                                  PP.getLangOpts(), PP.getPreprocessorOpts());
 }
 
 void PCHValidator::ReadCounter(const ModuleFile &M, unsigned Value) {
   PP.setCounterValue(Value);
 }
 
 //===----------------------------------------------------------------------===//
 // AST reader implementation
bool ReadTargetOptions(const TargetOptions &TargetOpts, bool Complain,
       return checkTargetOptions(ExistingTargetOpts, TargetOpts, nullptr,
                                 AllowCompatibleDifferences);
     }
 
     bool ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                  StringRef SpecificModuleCachePath,
                                  bool Complain) override {
       return checkHeaderSearchOptions(HSOpts, SpecificModuleCachePath,
-                                      ExistingModuleCachePath,
-                                      nullptr, ExistingLangOpts);
+                                      ExistingModuleCachePath, nullptr,
+                                      ExistingLangOpts, ExistingPPOpts);
     }
 
     bool ReadPreprocessorOptions(const PreprocessorOptions &PPOpts,
                                  bool Complain,
                                  std::string &SuggestedPredefines) override {
       return checkPreprocessorOptions(ExistingPPOpts, PPOpts, nullptr, FileMgr,
                                       SuggestedPredefines, ExistingLangOpts);
     }

clang/test/Modules/Inputs/pch-typedef.h

+typedef int pch_int;

clang/test/Modules/module-pch-different-cache-path.c

+// RUN: rm -rf %t
+// RUN: mkdir %t
+//
+// RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-typedef.h -o %t/pch-typedef.h.gch \
+// RUN:   -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/one
+//
+// RUN: not %clang_cc1 -x objective-c -fsyntax-only %s -include-pch %t/pch-typedef.h.gch \
+// RUN:   -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/two 2>&1 \
+// RUN:   | FileCheck %s -check-prefixes=CHECK-ERROR
+//
+// RUN: %clang_cc1 -x objective-c -fsyntax-only %s -include-pch %t/pch-typedef.h.gch \
+// RUN:   -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/two 2>&1 -fallow-pch-with-different-modules-cache-path \
+// RUN:   | FileCheck %s -check-prefixes=CHECK-SUCCESS -allow-empty
+
+pch_int x = 0;
+
+// CHECK-ERROR: PCH was compiled with module cache path '{{.*}}', but the path is currently '{{.*}}'
+// CHECK-SUCCESS-NOT: PCH was compiled with module cache path '{{.*}}', but the path is currently '{{.*}}'