Handle stray LoadExprs in RawRepresentable fix-its (#17847)

When there are multiple possible overloads for a call, the partially-
type-checked argument expression might end up with a LoadExpr outside
of the call ParenExpr instead of inside it. Account for this in a one-
off way for the 'rawValue' / 'init(rawValue:)' fix-its.

Yet more https://bugs.swift.org/browse/SR-8150

(cherry picked from commit c468ca1)

Author: jrose-apple

lib/Sema/CSDiag.cpp

@@ -4535,8 +4535,14 @@ static bool diagnoseRawRepresentableMismatch(CalleeCandidateInfo &CCI,
     return false;
 
   const Expr *expr = argExpr;
-  if (auto *tupleArgs = dyn_cast<TupleExpr>(argExpr))
+  if (auto *tupleArgs = dyn_cast<TupleExpr>(argExpr)) {
     expr = tupleArgs->getElement(bestMatchIndex);
+  } else if (auto *misplacedLoad = dyn_cast<LoadExpr>(argExpr)) {
+    // If there are multiple possible overloads for a single-argument call
+    // expression, the partially-typed-checked AST may have a load around the
+    // call parentheses instead of inside them.
+    expr = misplacedLoad->getSubExpr();
+  }
   expr = expr->getValueProvidingExpr();
 
   auto parameters = bestMatchCandidate->getUncurriedFunctionType()->getParams();

test/Sema/enum_raw_representable.swift

@@ -168,6 +168,19 @@ func sr8150(bar: Bar) {
   // expected-error@-1 {{cannot convert value of type 'Double' to expected argument type 'Bar'}} {{18-18=Bar(rawValue: }} {{21-21=)}}
 }
 
+class SR8150Box {
+  var bar: Bar
+  init(bar: Bar) { self.bar = bar }
+}
+// Bonus problem with mutable values being passed.
+func sr8150_mutable(obj: SR8150Box) {
+  sr8150_helper1(obj.bar)
+  // expected-error@-1 {{cannot convert value of type 'Bar' to expected argument type 'Double'}} {{18-18=}} {{25-25=.rawValue}}
+
+  var bar = obj.bar
+  sr8150_helper1(bar)
+  // expected-error@-1 {{cannot convert value of type 'Bar' to expected argument type 'Double'}} {{18-18=}} {{21-21=.rawValue}}
+}
 
 struct NotEquatable { }