addressing comments on PR

- moving WARNING definition from DiagnosticsCommon.def to DiagnosticsSema.def
- improving WARNING message to better align with guidelines described in docs/Diagnostics.md as suggested by @xwu.
- adapting expected warning message in tests.

Author: vguerra

include/swift/AST/DiagnosticsCommon.def

@@ -54,10 +54,6 @@ NOTE(previous_decldef,none,
 NOTE(brace_stmt_suggest_do,none,
      "did you mean to use a 'do' statement?", ())
 
-WARNING(defer_stmt_at_block_end,none,
-     "'defer' at the end of its scope is redundant and will execute immediately; "
-     "replace it with 'do'", ())
-
 // Generic disambiguation
 NOTE(while_parsing_as_left_angle_bracket,none,
      "while parsing this '<' as a type parameter bracket", ())

include/swift/AST/DiagnosticsSema.def

@@ -3033,6 +3033,10 @@ ERROR(jump_out_of_defer,none,
       "'%0' cannot transfer control out of a defer statement",
       (StringRef))
 
+WARNING(defer_stmt_at_block_end,none,
+     "'defer' statement before end of scope always executes immediately; "
+     "replace with 'do' statement to silence this warning", ())
+
 ERROR(return_invalid_outside_func,none,
       "return invalid outside of a func", ())
 

test/SILGen/statements.swift

@@ -524,7 +524,7 @@ func defer_in_closure_in_generic<T>(_ x: T) {
   // CHECK-LABEL: sil private @$S10statements017defer_in_closure_C8_genericyyxlFyycfU_ : $@convention(thin) <T> () -> ()
   _ = {
     // CHECK-LABEL: sil private @$S10statements017defer_in_closure_C8_genericyyxlFyycfU_6$deferL_yylF : $@convention(thin) <T> () -> ()
-    defer { generic_callee_1(T.self) } // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{5-10=do}}
+    defer { generic_callee_1(T.self) } // expected-warning {{'defer' statement before end of scope always executes immediately}}{{5-10=do}}
   }
 }
 
@@ -537,7 +537,7 @@ func defer_mutable(_ x: Int) {
   // CHECK: function_ref @$S10statements13defer_mutableyySiF6$deferL_yyF : $@convention(thin) (@inout_aliasable Int) -> ()
   // CHECK-NOT: [[BOX]]
   // CHECK: destroy_value [[BOX]]
-  defer { _ = x } // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{3-8=do}}
+  defer { _ = x } // expected-warning {{'defer' statement before end of scope always executes immediately}}{{3-8=do}}
 }
 
 protocol StaticFooProtocol { static func foo() }

test/SILOptimizer/definite_init_diagnostics_globals.swift

@@ -21,7 +21,7 @@ defer { print(y) } // expected-error {{constant 'y' used in defer before being i
 // Test top-level functions.
 
 func testFunc() {       // expected-error {{variable 'x' used by function definition before being initialized}}
-  defer { print(x) }    // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{3-8=do}}
+  defer { print(x) }    // expected-warning {{'defer' statement before end of scope always executes immediately}}{{3-8=do}}
 }
 
 // Test top-level closures.

test/SILOptimizer/unreachable_code.swift

@@ -285,7 +285,7 @@ func deferTryNoReturn() throws {
 }
 
 func noReturnInDefer() {
-  defer { // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{3-8=do}}
+  defer { // expected-warning {{'defer' statement before end of scope always executes immediately}}{{3-8=do}}
     _ = Lisp()
     die() // expected-note {{a call to a never-returning function}}
     die() // expected-warning {{will never be executed}}

test/Sema/diag_defer_block_end.swift

@@ -3,14 +3,14 @@
 let x = 1
 let y = 2
 if (x > y) {
-    defer { // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{5-10=do}}
+    defer { // expected-warning {{'defer' statement before end of scope always executes immediately}}{{5-10=do}}
         print("not so useful defer stmt.")
     }
 }
 
 func sr7307(_ value: Bool) {
     let negated = !value 
-    defer { // expected-warning {{'defer' at the end of its scope is redundant and will execute immediately}}{{5-10=do}}
+    defer { // expected-warning {{'defer' statement before end of scope always executes immediately}}{{5-10=do}}
         print("negated value is {negated}")
     }
 }

test/stmt/statements.swift

@@ -342,17 +342,17 @@ func test_defer(_ a : Int) {
 
   // Not ok.
   while false { defer { break } }   // expected-error {{'break' cannot transfer control out of a defer statement}}
-  // expected-warning@-1 {{'defer' at the end of its scope is redundant and will execute immediately}}{{17-22=do}}
+  // expected-warning@-1 {{'defer' statement before end of scope always executes immediately}}{{17-22=do}}
   defer { return }  // expected-error {{'return' cannot transfer control out of a defer statement}}
-  // expected-warning@-1 {{'defer' at the end of its scope is redundant and will execute immediately}}{{3-8=do}}
+  // expected-warning@-1 {{'defer' statement before end of scope always executes immediately}}{{3-8=do}}
 }
 
 class SomeTestClass {
   var x = 42
 
   func method() {
     defer { x = 97 }  // self. not required here!
-    // expected-warning@-1 {{'defer' at the end of its scope is redundant and will execute immediately}}{{5-10=do}}
+    // expected-warning@-1 {{'defer' statement before end of scope always executes immediately}}{{5-10=do}}
   }
 }
 

test/stmt/yield.swift

@@ -82,7 +82,7 @@ func call_yield() {
 struct YieldInDefer {
   var property: String {
     _read {
-      defer {
+      defer { // expectd-warning {{'defer' statement before end of scope always executes immediately}}{{7-12=do}}
         // FIXME: this recovery is terrible
         yield ""
         // expected-error@-1 {{expression resolves to an unused function}}