Fix OOM in FormatDiagnostic (2nd attempt) (#108866)

Resolves: #70930 (and probably latest comments from clangd/clangd#251)
by fixing racing for the shared DiagStorage value which caused messing with args inside the storage and then formatting the following message with getArgSInt(1) == 2:

def err_module_odr_violation_function : Error<
  "%q0 has different definitions in different modules; "
  "%select{definition in module '%2'|defined here}1 "
  "first difference is "

which causes HandleSelectModifier to go beyond the ArgumentLen so the recursive call to FormatDiagnostic was made with DiagStr > DiagEnd that leads to infinite while (DiagStr != DiagEnd).

The Main Idea:
Reuse the existing DiagStorageAllocator logic to make all DiagnosticBuilders having independent states.
Also, encapsulating the rest of state (e.g. ID and Loc) into DiagnosticBuilder.

The last attempt failed -
#108187 (comment)
so was reverted - #108838

Author: igelbox

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -380,7 +380,6 @@ void ClangTidyDiagnosticConsumer::HandleDiagnostic(
     ++Context.Stats.ErrorsIgnoredNOLINT;
     // Ignored a warning, should ignore related notes as well
     LastErrorWasIgnored = true;
-    Context.DiagEngine->Clear();
     for (const auto &Error : SuppressionErrors)
       Context.diag(Error);
     return;
@@ -457,7 +456,6 @@ void ClangTidyDiagnosticConsumer::HandleDiagnostic(
   if (Info.hasSourceManager())
     checkFilters(Info.getLocation(), Info.getSourceManager());
 
-  Context.DiagEngine->Clear();
   for (const auto &Error : SuppressionErrors)
     Context.diag(Error);
 }

clang-tools-extra/clangd/unittests/ConfigCompileTests.cpp

@@ -305,33 +305,33 @@ TEST_F(ConfigCompileTests, DiagnosticSuppression) {
   {
     auto D = DiagEngine.Report(diag::warn_unreachable);
     EXPECT_TRUE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
   // Subcategory not respected/suppressed.
   {
     auto D = DiagEngine.Report(diag::warn_unreachable_break);
     EXPECT_FALSE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
   {
     auto D = DiagEngine.Report(diag::warn_unused_variable);
     EXPECT_TRUE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
   {
     auto D = DiagEngine.Report(diag::err_typecheck_bool_condition);
     EXPECT_TRUE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
   {
     auto D = DiagEngine.Report(diag::err_unexpected_friend);
     EXPECT_TRUE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
   {
     auto D = DiagEngine.Report(diag::warn_alloca);
     EXPECT_TRUE(isDiagnosticSuppressed(
-        Diag{&DiagEngine}, Conf.Diagnostics.Suppress, LangOptions()));
+        Diag{&DiagEngine, D}, Conf.Diagnostics.Suppress, LangOptions()));
   }
 
   Frag.Diagnostics.Suppress.emplace_back("*");