[Fixit] Suggested by Jordan, check immutability before adding ampersand.

Author: nkcsgexi

Diff for: lib/Sema/CSDiag.cpp

@@ -3495,7 +3495,7 @@ bool FailureDiagnosis::diagnoseContextualConversionError() {
                contextDecl == CS->TC.Context.getUnsafeMutablePointerDecl()) {
       SmallVector<Type, 4> scratch;
       for (Type arg : contextualType->getAllGenericArgs(scratch)) {
-        if (arg->isEqual(exprType)) {
+        if (arg->isEqual(exprType) && expr->getType()->isLValueType()) {
           diagnose(expr->getLoc(), diagID, exprType, contextualType).
             fixItInsert(expr->getStartLoc(), "&");
           return true;

Diff for: test/Sema/diag_type_conversion.swift

@@ -4,9 +4,14 @@ func foo1(_ a: [Int]) {}
 func foo2(_ a : UnsafePointer<Int>) {}
 func foo4(_ a : UnsafeMutablePointer<Int>) {}
 func foo3 () {
-  foo1(1) // expected-error {{cannot convert value of type 'Int' to expected argument type '[Int]'}} {{8-8=[}} {{9-9=]}}
-  foo2(1) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafePointer<Int>'}} {{8-8=&}}
-  var j = 3
-  foo2(j) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafePointer<Int>'}} {{8-8=&}}
-  foo4(j) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafeMutablePointer<Int>'}} {{8-8=&}}
+  let j = 3
+  foo2(j) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafePointer<Int>'}} {{none}}
+  foo4(j) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafeMutablePointer<Int>'}} {{none}}
+
+  var i = 3
+  foo2(i) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafePointer<Int>'}} {{8-8=&}}
+  foo4(i) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafeMutablePointer<Int>'}} {{8-8=&}}
+
+  foo2(1) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafePointer<Int>'}} {{none}}
+  foo4(1) // expected-error {{cannot convert value of type 'Int' to expected argument type 'UnsafeMutablePointer<Int>'}} {{none}}
 }