[-Wunsafe-buffer-usage] Create Fix-Its only if they are emitted

[jkorous]

clang/lib/Analysis/UnsafeBufferUsage.cpp

1020

Since our current plan is to also change type of variables that don't directly participate in unsafe operations but would lead to correct bounds propagation the assumption in this FIXME might not be correct anymore.

I originally intended to address the FIXME in this patch but ended up just discarding it.

[NoQ]

clang/lib/Analysis/UnsafeBufferUsage.cpp

1020

Hmm, these are kind of separate.

If we're running under -fno-diagnostics-fixit-info, then yeah, we should still identify all variables that need to be fixed and explain them in notes.

If we're running below C++20, then in addition to that, we also shouldn't leave notes about "You should change this thing to span!" given that span doesn't exist.

[NoQ]

This is probably good to go either way, we can address the note problem separately. The patch is NFC, purely a performance thing, so no tests are needed.

[jkorous]

clang/lib/Analysis/UnsafeBufferUsage.cpp

1020

You are right. Let's address that in a future patch.

clang/lib/Analysis/UnsafeBufferUsage.cpp

void clang::checkUnsafeBufferUsage(const Decl *D,
                                    bool EmitFixits) {
   assert(D && D->getBody());
 
   WarningGadgetSets UnsafeOps;
   FixableGadgetSets FixablesForUnsafeVars;
   DeclUseTracker Tracker;
 
   {
-    // FIXME: We could skip even matching Fixables' matchers if EmitFixits ==
-    // false.
     auto [FixableGadgets, WarningGadgets, TrackerRes] = findGadgets(D, Handler);
     UnsafeOps = groupWarningGadgetsByVar(std::move(WarningGadgets));
     FixablesForUnsafeVars = groupFixablesByVar(std::move(FixableGadgets));
     Tracker = std::move(TrackerRes);
   }
 
   std::map<const VarDecl *, FixItList> FixItsForVariable;
 

clang/lib/Sema/AnalysisBasedWarnings.cpp

if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
         checkThrowInNonThrowingFunc(S, FD, AC);
 
   // Emit unsafe buffer usage warnings and fixits.
   if (!Diags.isIgnored(diag::warn_unsafe_buffer_operation, D->getBeginLoc()) ||
       !Diags.isIgnored(diag::warn_unsafe_buffer_variable, D->getBeginLoc())) {
     UnsafeBufferUsageReporter R(S);
     checkUnsafeBufferUsage(
         D, R,
-        /*EmitFixits=*/S.getLangOpts().CPlusPlus20);
+        /*EmitFixits=*/S.getDiagnostics().getDiagnosticOptions().ShowFixits &&
+            S.getLangOpts().CPlusPlus20);
   }
 
   // If none of the previous checks caused a CFG build, trigger one here
   // for the logical error handler.
   if (LogicalErrorHandler::hasActiveDiagnostics(Diags, D->getBeginLoc())) {
     AC.getCFG();
   }