Serialization: Merge three diagnostics to simplify ASTReader::getInputFile, NFC

[dexonsmith]

Summary

Clean up the logic for err_fe_{pch,module,ast}_file_modified to use a
select like other ASTReader diagnostics. There should be no
functionality change here, just a cleanup.

[jansvoboda11]

Getting rid of the duplication is definitely nice. I left one inline question about the terminology used.

clang/include/clang/Basic/DiagnosticSerializationKinds.td

19–21

I'm a bit confused by the fact that a diagnostic with pch_file in its name might output module file or AST file as well.

This file already contains a couple diagnostics that use a similar %select and have module in their name (e.g. err_module_file_out_of_date). Would it make sense to unify the terminology here?

[dexonsmith]

clang/include/clang/Basic/DiagnosticSerializationKinds.td

19–21

Yeah, I wasn't sure what to do about that. module is also wrong. I ended up choosing pch just since the diagnostic was in a group of pch diagnostics.

IMO, the best name for all of these is ast since that's the most generic term. I could rename the others to ast in a prep commit and then update this patch to use ast as well. WDYT?

[dexonsmith]

Rename to use ast_ to match https://reviews.llvm.org/D91436.

[jansvoboda11]

LGTM

clang/include/clang/Basic/DiagnosticSerializationKinds.td

19–21

Sounds good.

clang/include/clang/Basic/DiagnosticSerializationKinds.td

 
 def err_fe_unable_to_read_pch_file : Error<
     "unable to read PCH file %0: '%1'">;
 def err_fe_not_a_pch_file : Error<
     "input is not a PCH file: '%0'">;
 def err_fe_pch_malformed : Error<
     "malformed or corrupted AST file: '%0'">, DefaultFatal;
 def err_fe_pch_malformed_block : Error<
     "malformed block record in PCH file: '%0'">, DefaultFatal;
-def err_fe_pch_file_modified : Error<
-    "file '%0' has been modified since the precompiled header '%1' was built"
-    ": %select{size|mtime|content}2 changed">,
-    DefaultFatal;
-def err_fe_module_file_modified : Error<
-    "file '%0' has been modified since the module file '%1' was built"
-    ": %select{size|mtime|content}2 changed">,
-    DefaultFatal;
 def err_fe_ast_file_modified : Error<
-    "file '%0' has been modified since the AST file '%1' was built"
-    ": %select{size|mtime|content}2 changed">,
+    "file '%0' has been modified since the "
+    "%select{precompiled header|module file|AST file}1 '%2' was built"
+    ": %select{size|mtime|content}3 changed">,
     DefaultFatal;
 def err_fe_pch_file_overridden : Error<
     "file '%0' from the precompiled header has been overridden">;
 def note_pch_required_by : Note<"'%0' required by '%1'">;
 def note_pch_rebuild_required : Note<"please rebuild precompiled header '%0'">;
 def note_module_cache_path : Note<
     "after modifying system headers, please delete the module cache at '%0'">;
 

clang/lib/Serialization/ASTReader.cpp

if (!Overridden && FileChange != ModificationType::None) {
     if (Complain && !Diags.isDiagnosticInFlight()) {
       // Build a list of the PCH imports that got us here (in reverse).
       SmallVector<ModuleFile *, 4> ImportStack(1, &F);
       while (!ImportStack.back()->ImportedBy.empty())
         ImportStack.push_back(ImportStack.back()->ImportedBy[0]);
 
       // The top-level PCH is stale.
       StringRef TopLevelPCHName(ImportStack.back()->FileName);
-      unsigned DiagnosticKind =
-          moduleKindForDiagnostic(ImportStack.back()->Kind);
-      if (DiagnosticKind == 0)
-        Diag(diag::err_fe_pch_file_modified)
-            << Filename << TopLevelPCHName << FileChange;
-      else if (DiagnosticKind == 1)
-        Diag(diag::err_fe_module_file_modified)
-            << Filename << TopLevelPCHName << FileChange;
-      else
-        Diag(diag::err_fe_ast_file_modified)
-            << Filename << TopLevelPCHName << FileChange;
+          << Filename << moduleKindForDiagnostic(ImportStack.back()->Kind)
+          << TopLevelPCHName << FileChange;
 
       // Print the import stack.
       if (ImportStack.size() > 1) {
         Diag(diag::note_pch_required_by)
           << Filename << ImportStack[0]->FileName;
         for (unsigned I = 1; I < ImportStack.size(); ++I)
           Diag(diag::note_pch_required_by)
             << ImportStack[I-1]->FileName << ImportStack[I]->FileName;