[Sema] Avoid marking TypeRepr invalid with SilenceErrors

Pattern resolution currently invokes type resolution with this flag
since it's trying to see if it can treat a given expression as a
TypeRepr for e.g an enum pattern. Make sure we don't `setInvalid` on
such TypeRepr nodes since that will avoid diagnosing in cases where
the node also then gets treated as a TypeRepr for an ExprPattern,
where we actually want the diagnostic emitted.

Author: hamishknight

lib/Sema/TypeCheckType.cpp

@@ -2637,10 +2637,12 @@ static Type evaluateTypeResolution(const TypeResolution *resolution,
       TypeResolver(*resolution, silContext)
           .resolveType(TyR, resolution->getOptions());
 
-  // If we resolved down to an error, make sure to mark the typeRepr as invalid
-  // so we don't produce a redundant diagnostic.
+  // If we resolved down to an error, and we haven't silenced diagnostics, make
+  // sure to mark the typeRepr as invalid so we don't produce a redundant
+  // diagnostic.
   if (result->hasError()) {
-    TyR->setInvalid();
+    if (!options.contains(TypeResolutionFlags::SilenceErrors))
+      TyR->setInvalid();
     return result;
   }
 

test/Constraints/patterns.swift

@@ -820,3 +820,17 @@ do {
     }
   }
 }
+
+// Make sure we diagnose 'Undefined' here.
+func testUndefinedTypeInPattern(_ x: Int) {
+  switch x {
+  case Optional<Undefined>.alsoUndefined: // expected-error {{cannot find type 'Undefined' in scope}}
+    break
+  }
+  _ = {
+    switch x {
+    case Optional<Undefined>.alsoUndefined: // expected-error {{cannot find type 'Undefined' in scope}}
+      break
+    }
+  }
+}

…ompiler_crashers_2/75d8fd688b445bb.swift …r_crashers_2_fixed/75d8fd688b445bb.swiftvalidation-test/compiler_crashers_2/75d8fd688b445bb.swift renamed to validation-test/compiler_crashers_2_fixed/75d8fd688b445bb.swift validation-test/compiler_crashers_2/75d8fd688b445bb.swift renamed to validation-test/compiler_crashers_2_fixed/75d8fd688b445bb.swift

@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"b7a10f72","signature":"(anonymous namespace)::Verifier::walkToExprPre(swift::Expr*)","signatureAssert":"Assertion failed: ((HadError || !isa<SourceFile *>(M) || cast<SourceFile *>(M)->ASTStage < SourceFile::TypeChecked) && \"OverloadedDeclRef\" \"in wrong phase\"), function walkToExprPre"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 func a(b : Int) {
   _ = {
     switch b {