[AST][RecoveryExpr] Fix an assertion crash on openMP.

[hokein]

Summary

With recovery expr, it is possible that we have a value-dependent expr
within non-dependent context.

[sammccall]

This seems vaguely reasonable to me, but I don't really know what an OpenMP capture is.

@ABataev, @jdoerfert : Any thoughts or concerns here?
Some context: an expression that contains errors can exist after certain types of sema/parse errors and acts as a placeholder in the AST with unknown semantics, e.g. we often don't know what its type is.
It is modeled as dependent, but its value/type/validity depends on how an the user would correct the error rather than how a template is instantiated.
(This behavior is with the -recovery-ast flag, which will one day be default).

@hokein Callers of isDependentContext() might mike sense to audit for recovery-AST-safety as it gives fewer guarantees than it used to.

[ABataev]

LG

[jdoerfert]

Thx!

clang/lib/Sema/SemaOpenMP.cpp

bool OpenMPIterationSpaceChecker::checkAndSetInc(Expr *S) {
   SemaRef.Diag(S->getBeginLoc(), diag::err_omp_loop_not_canonical_incr)
       << S->getSourceRange() << LCDecl;
   return true;
 }
 
 static ExprResult
 tryBuildCapture(Sema &SemaRef, Expr *Capture,
                 llvm::MapVector<const Expr *, DeclRefExpr *> &Captures) {
-  if (SemaRef.CurContext->isDependentContext())
-    return ExprResult(Capture);
+  if (SemaRef.CurContext->isDependentContext() || Capture->containsErrors())
+    return Capture;
   if (Capture->isEvaluatable(SemaRef.Context, Expr::SE_AllowSideEffects))
     return SemaRef.PerformImplicitConversion(
         Capture->IgnoreImpCasts(), Capture->getType(), Sema::AA_Converting,
         /*AllowExplicit=*/true);
   auto I = Captures.find(Capture);
   if (I != Captures.end())
     return buildCapture(SemaRef, Capture, I->second);
   DeclRefExpr *Ref = nullptr;

clang/test/OpenMP/recovery-crash.cpp

+// RUN: %clang_cc1 -verify -fopenmp -fopenmp-version=50 -frecovery-ast %s
+
+void foo(int i) {
+#pragma omp target update from(i) device(undef()) // expected-error {{use of undeclared identifier 'undef'}}
+}