[clangd] check for synthesized symbols when tracking include locations (#75128)

This fixes #75115

In C mode with MSVC compatibility, when the `assert` macro is defined,
as a workaround, `static_assert` is implicitly defined as well, if not
already so, in order to work around a broken `assert.h` implementation.
This workaround was implemented in
8da0903

A synthesized symbol does not occur in source code, and therefore should
not have valid source location, but this was not checked when inserting
this into a `symbol -> include file` map.

The invalid FileID value is used for empty key representation in the
include file hash table, so it's not valid to insert it.

Author: mizvekov

clang-tools-extra/clangd/index/SymbolCollector.cpp

@@ -821,7 +821,8 @@ void SymbolCollector::setIncludeLocation(const Symbol &S, SourceLocation DefLoc,
 
   // Use the expansion location to get the #include header since this is
   // where the symbol is exposed.
-  IncludeFiles[S.ID] = SM.getDecomposedExpansionLoc(DefLoc).first;
+  if (FileID FID = SM.getDecomposedExpansionLoc(DefLoc).first; FID.isValid())
+    IncludeFiles[S.ID] = FID;
 
   // We update providers for a symbol with each occurence, as SymbolCollector
   // might run while parsing, rather than at the end of a translation unit.
@@ -879,16 +880,15 @@ void SymbolCollector::finish() {
     const Symbol *S = Symbols.find(SID);
     if (!S)
       continue;
-    assert(IncludeFiles.contains(SID));
 
-    const auto FID = IncludeFiles.at(SID);
+    FileID FID = IncludeFiles.lookup(SID);
     // Determine if the FID is #include'd or #import'ed.
     Symbol::IncludeDirective Directives = Symbol::Invalid;
     auto CollectDirectives = shouldCollectIncludePath(S->SymInfo.Kind);
     if ((CollectDirectives & Symbol::Include) != 0)
       Directives |= Symbol::Include;
     // Only allow #import for symbols from ObjC-like files.
-    if ((CollectDirectives & Symbol::Import) != 0) {
+    if ((CollectDirectives & Symbol::Import) != 0 && FID.isValid()) {
       auto [It, Inserted] = FileToContainsImportsOrObjC.try_emplace(FID);
       if (Inserted)
         It->second = FilesWithObjCConstructs.contains(FID) ||

clang-tools-extra/clangd/test/GH75115.test

@@ -0,0 +1,15 @@
+// RUN: rm -rf %t.dir && mkdir -p %t.dir
+// RUN: echo '[{"directory": "%/t.dir", "command": "clang --target=x86_64-pc-windows-msvc -x c GH75115.test", "file": "GH75115.test"}]' > %t.dir/compile_commands.json
+// RUN: clangd -enable-config=0 --compile-commands-dir=%t.dir -check=%s 2>&1 | FileCheck -strict-whitespace %s
+
+// CHECK: Building preamble...
+// CHECK-NEXT: Built preamble
+// CHECK-NEXT: Indexing headers...
+// CHECK-NEXT: Building AST...
+// CHECK-NEXT: Indexing AST...
+// CHECK-NEXT: Building inlay hints
+// CHECK-NEXT: semantic highlighting
+// CHECK-NEXT: Testing features at each token
+// CHECK-NEXT: All checks completed, 0 errors
+
+#define assert