[reference-bindings] Make the never mutated diagnostic only apply to vars, not also to inout bindings.

Author: gottesmm

lib/Sema/MiscDiagnostics.cpp

@@ -3526,7 +3526,8 @@ VarDeclUsageChecker::~VarDeclUsageChecker() {
 
     // If this is a mutable 'var', and it was never written to, suggest
     // upgrading to 'let'.
-    if (!var->isLet() && (access & RK_Written) == 0 &&
+    if (var->getIntroducer() == VarDecl::Introducer::Var
+        && (access & RK_Written) == 0 &&
         // Don't warn if we have something like "let (x,y) = ..." and 'y' was
         // never mutated, but 'x' was.
         !isVarDeclPartOfPBDThatHadSomeMutation(var)) {

test/SILOptimizer/reference_bindings.swift

@@ -3,19 +3,16 @@
 func varBindingTest() {
     var x = "1"
     x = "1"
-    inout x1 = x // expected-warning {{variable 'x1' was never mutated; consider changing to 'let' constant}}
-    // expected-error @-1 {{overlapping accesses to 'x', but modification requires exclusive access; consider copying to a local variable}}
+    inout x1 = x // expected-error {{overlapping accesses to 'x', but modification requires exclusive access; consider copying to a local variable}}
     let _ = x1
     inout x2 = x // expected-note {{conflicting access is here}}
-    // expected-warning @-1 {{variable 'x2' was never mutated; consider changing to 'let' constant}}
     let _ = x2
 }
 
 func varBindingTest2() {
     var x = "1"
     x = "1"
-    inout x1 = x // expected-warning {{variable 'x1' was never mutated; consider changing to 'let' constant}}
-    // expected-error @-1 {{overlapping accesses to 'x', but modification requires exclusive access; consider copying to a local variable}}
+    inout x1 = x // expected-error {{overlapping accesses to 'x', but modification requires exclusive access; consider copying to a local variable}}
     let _ = x1
     x = "2" // expected-note {{conflicting access is here}}
 }
@@ -24,7 +21,7 @@ func varBindingTest3() {
     var x = "1"
     x = "1"
     do {
-      inout x1 = x // expected-warning {{variable 'x1' was never mutated; consider changing to 'let' constant}}
+      inout x1 = x
       let _ = x1
     }
     x = "2"

test/Sema/reference_bindings.swift

@@ -52,3 +52,16 @@ func foo(_ arg: String, _ consumingArg: consuming String, _ borrowingArg: borrow
     inout getterStructVarFieldX = varStruct.sGetter // expected-error {{inout bindings must be bound to an lvalue}}
     inout modifyStructVarFieldX = varStruct.sModify
 }
+
+// Make sure that we get never used to diagnostics, but not never written to diagnostics.
+func neverWrittenMutatedDiagnostics() {
+    var x = "123"
+    x = "223"
+    do {
+        inout x2 = x // expected-warning {{initialization of variable 'x2' was never used; consider replacing with assignment to '_' or removing it}}
+    }
+    do {
+        inout x2 = x
+        let _ = x2
+    }
+}