[clang-doc] concatenate SymbolIDs to truncated mangled names (llvm#159490)

Previously, if mangled names were too long to be used as filenames, the
object's SymbolID was used as a filename. This worked for length
restrictions, but made URLs/filenames inconsistent. This patch truncates
the mangled name and appends the SymbolID. Thus, we can keep some
context in the URL/filename while preserving uniqueness.

Author: evelez7

clang-tools-extra/clang-doc/Serialize.cpp

@@ -780,12 +780,10 @@ static void populateSymbolInfo(SymbolInfo &I, const T *D, const FullComment *C,
     MangledStream << D->getNameAsString();
   // A 250 length limit was chosen since 255 is a common limit across
   // different filesystems, with a 5 character buffer for file extensions.
-  if (MangledName.size() > 250)
-    // File creation fails if the mangled name is too long, so default to the
-    // USR. We should look for a better check since filesystems differ in
-    // maximum filename length
-    I.MangledName = llvm::toStringRef(llvm::toHex(I.USR));
-  else
+  if (MangledName.size() > 250) {
+    auto SymbolID = llvm::toStringRef(llvm::toHex(I.USR)).str();
+    I.MangledName = MangledName.substr(0, 250 - SymbolID.size()) + SymbolID;
+  } else
     I.MangledName = MangledName;
   delete Mangler;
 }

clang-tools-extra/test/clang-doc/long-name.cpp

@@ -9,6 +9,6 @@ struct ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLong
 struct ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd123 {};
 
 // CHECK-JSON: ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd12.json
-// CHECK-JSON: {{[0-9A-F]*}}.json
+// CHECK-JSON: _ZTV244ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheL29DE8558215A13A506661C0E01E50AA3E5C9C7FA.json 
 // CHECK-HTML: ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd12.html
-// CHECK-HTML: {{[0-9A-F]*}}.html
+// CHECK-HTML: _ZTV244ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheL29DE8558215A13A506661C0E01E50AA3E5C9C7FA.html