[NFC] Lazily Construct ErrorTypes when PatternTypeRequest Fails

Doing this eagerly makes it more difficult to determine when something fails by observing the creation of ErrorTypes

Author: CodaFi

lib/Sema/TypeCheckPattern.cpp

@@ -732,8 +732,12 @@ static Type validateTypedPattern(TypedPattern *TP, TypeResolution resolution) {
 Type TypeChecker::typeCheckPattern(ContextualPattern pattern) {
   DeclContext *dc = pattern.getDeclContext();
   ASTContext &ctx = dc->getASTContext();
-  return evaluateOrDefault(
-      ctx.evaluator, PatternTypeRequest{pattern}, ErrorType::get(ctx));
+  if (auto type = evaluateOrDefault(ctx.evaluator, PatternTypeRequest{pattern},
+                                    Type())) {
+    return type;
+  }
+
+  return ErrorType::get(ctx);
 }
 
 /// Apply the contextual pattern's context to the type resolution options.

lib/Sema/TypeCheckType.cpp

@@ -1207,9 +1207,8 @@ static Type diagnoseUnknownType(TypeResolution resolution,
       return I->second;
     }
 
-    diags.diagnose(L, diag::cannot_find_type_in_scope,
-                comp->getNameRef())
-      .highlight(R);
+    diags.diagnose(L, diag::cannot_find_type_in_scope, comp->getNameRef())
+        .highlight(R);
 
     return ErrorType::get(ctx);
   }