[CS] Avoid emitting invalid binding diagnostic in more cases

Also avoid emitting the diagnostic for an out of
place binding pattern if there's an existing fix
on a parent call expression, as that's the real
source of the failure.

rdar://113025351

Author: hamishknight

lib/Sema/CSDiagnostics.cpp

@@ -8365,12 +8365,13 @@ bool InvalidEmptyKeyPathFailure::diagnoseAsError() {
 }
 
 bool InvalidPatternInExprFailure::diagnoseAsError() {
-  // Check to see if we have something like 'case <fn>(let foo)', where <fn>
-  // has a fix associated with it. In such a case, it's more likely than not
-  // that the user is trying to write an EnumElementPattern, but has made some
-  // kind of mistake in the function expr that causes it to be treated as an
-  // ExprPattern. Emitting an additional error for the out of place 'let foo' is
-  // just noise in that case, so let's avoid diagnosing.
+  // Check to see if we have something like 'case <fn>(let foo)', where either
+  // <fn> or the call itself has a fix associated with it. In such a case, it's
+  // more likely than not that the user is trying to write an
+  // EnumElementPattern, but has made some kind of mistake in the function expr
+  // that causes it to be treated as an ExprPattern. Emitting an additional
+  // error for the out of place 'let foo' is just noise in that case, so let's
+  // avoid diagnosing.
   llvm::SmallPtrSet<Expr *, 4> fixAnchors;
   for (auto *fix : getSolution().Fixes) {
     if (auto *anchor = getAsExpr(fix->getAnchor()))
@@ -8380,7 +8381,7 @@ bool InvalidPatternInExprFailure::diagnoseAsError() {
     auto *E = castToExpr(getLocator()->getAnchor());
     while (auto *parent = findParentExpr(E)) {
       if (auto *CE = dyn_cast<CallExpr>(parent)) {
-        if (fixAnchors.contains(CE->getFn()))
+        if (fixAnchors.contains(CE) || fixAnchors.contains(CE->getFn()))
           return false;
       }
       E = parent;

test/Constraints/rdar113025351.swift

@@ -0,0 +1,23 @@
+// RUN: %target-typecheck-verify-swift
+
+struct S {
+  enum E: Error {
+    case e(Int)
+    case f
+  }
+}
+
+func foo() throws {}
+
+// rdar://113025351: Avoid emitting a separate diagnostic complaining that a
+// 'let' cannot be nested in an expression, as it just adds noise.
+func bar() throws {
+  do {
+    try foo()
+  } catch S.E(let x) {} // expected-error {{'S.E' cannot be constructed because it has no accessible initializers}}
+}
+
+func baz(_ x: S.E) {
+  if case S.E(let y) = x {} // expected-error {{'S.E' cannot be constructed because it has no accessible initializers}}
+  if case S.E(S.E.e(let y)) = x {} // expected-error {{'S.E' cannot be constructed because it has no accessible initializers}}
+}