[Parser] Fix the assertion crash in ActOnStartOfSwitch stmt.

[hokein]

Summary

After we parse the switch condition, we don't do the type check for
type-dependent expr (e.g. TypoExpr) (in Sema::CheckSwitchCondition), then the
TypoExpr is corrected to an invalid-type expr (in Sema::MakeFullExpr) and passed
to the ActOnStartOfSwitchStmt, which triggers the assertion.

Fix https://github.com/clangd/clangd/issues/311

[sammccall]

clang/lib/Sema/SemaStmt.cpp

709

How do we know Cond is a TypoExpr directly rather than containing one?

I think the usual strategy when code can't deal with typo correction being delayed further is to call CorrectDelayedTyposInExpr.

[hokein]

clang/lib/Sema/SemaStmt.cpp

709

no sure whether we should consider the containing-typo Cond, we might still want to keep the typo correction? thinking a case like switch(return_int(typo-expr)) {}.

Do you suggest that we use the CorrectDelayedTyposInExpr to check the whether Cond is/has a TypoExpr? CorrectDelayedTyposInExpr has a side effect of emitting the typo-suggestion diagnostic.

[hokein]

adjust the assertion based on the offline discussion.

[hokein]

fix a typo.

clang/lib/Sema/SemaStmt.cpp

SemaDiagnosticBuilder noteAmbiguous(
       << ConvTy->isEnumeralType() << ConvTy;
     }
 
     SemaDiagnosticBuilder diagnoseConversion(
         Sema &S, SourceLocation Loc, QualType T, QualType ConvTy) override {
       llvm_unreachable("conversion functions are permitted");
     }
   } SwitchDiagnoser(Cond);
 
   ExprResult CondResult =
       PerformContextualImplicitConversion(SwitchLoc, Cond, SwitchDiagnoser);
   if (CondResult.isInvalid())
     return ExprError();
 
   // FIXME: PerformContextualImplicitConversion doesn't always tell us if it
   // failed and produced a diagnostic.
   Cond = CondResult.get();
   if (!Cond->isTypeDependent() &&
       !Cond->getType()->isIntegralOrEnumerationType())
     return ExprError();
 
   // C99 6.8.4.2p5 - Integer promotions are performed on the controlling expr.
   return UsualUnaryConversions(Cond);
 }
 
 StmtResult Sema::ActOnStartOfSwitchStmt(SourceLocation SwitchLoc,
                                         Stmt *InitStmt, ConditionResult Cond) {
   Expr *CondExpr = Cond.get().second;
   assert((Cond.isInvalid() || CondExpr) && "switch with no condition");
 
   if (CondExpr && !CondExpr->isTypeDependent()) {
     // We have already converted the expression to an integral or enumeration
-    // type, when we parsed the switch condition. If we don't have an
-    // appropriate type now, enter the switch scope but remember that it's
-    // invalid.
-    assert(CondExpr->getType()->isIntegralOrEnumerationType() &&
-           "invalid condition type");
+    // type, when we parsed the switch condition. There are cases where we don't
+    // have an appropriate type, e.g. a typo-expr Cond was corrected to an
+    // inappropriate-type expr, we just return an error.
+    if (!CondExpr->getType()->isIntegralOrEnumerationType())
+      return StmtError();
     if (CondExpr->isKnownToHaveBooleanValue()) {
       // switch(bool_expr) {...} is often a programmer error, e.g.
       //   switch(n && mask) { ... }  // Doh - should be "n & mask".
       // One can always use an if statement instead of switch(bool_expr).
       Diag(SwitchLoc, diag::warn_bool_switch_condition)
           << CondExpr->getSourceRange();
     }
   }

clang/test/Parser/switch-typo-correction.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+namespace c { double xxx; } // expected-note{{'c::xxx' declared here}}
+namespace d { float xxx; }
+namespace z { namespace xxx {} }
+
+void crash() {
+  switch (xxx) {} // expected-error{{use of undeclared identifier 'xxx'; did you mean }}
+}