[Sema] Improve wording of a diagnostic

Make it clear the issue is the transfer of
control flow out of the `if`/`switch` expression.
Technically things like `break` and `continue` are
allowed, as long as they are not jumping out of
the expression.

Author: hamishknight

include/swift/AST/DiagnosticsSema.def

@@ -1331,7 +1331,7 @@ ERROR(single_value_stmt_branch_must_end_in_result,none,
       "non-expression branch of '%0' expression may only end with a 'throw'",
       (StmtKind))
 ERROR(cannot_jump_in_single_value_stmt,none,
-      "cannot '%0' in '%1' when used as expression",
+      "cannot use '%0' to transfer control out of '%1' expression",
       (StmtKind, StmtKind))
 WARNING(effect_marker_on_single_value_stmt,none,
       "'%0' has no effect on '%1' expression", (StringRef, StmtKind))

test/Constraints/issue-71273.swift

@@ -15,7 +15,7 @@ func testLocalFn() {
 func testLocalBinding() {
   bar() {
     let _ = if .random() { return () } else { 0 }
-    // expected-error@-1 {{cannot 'return' in 'if' when used as expression}}
+    // expected-error@-1 {{cannot use 'return' to transfer control out of 'if' expression}}
     return ()
   }
 }

test/Constraints/rdar114402042.swift

@@ -8,7 +8,7 @@ func test() {
   foo {
     bar(if true { return } else { return })
     // expected-error@-1 {{'if' may only be used as expression in return, throw, or as the source of an assignment}}
-    // expected-error@-2 2{{cannot 'return' in 'if' when used as expression}}
+    // expected-error@-2 2{{cannot use 'return' to transfer control out of 'if' expression}}
   }
   foo {
     bar(if true { { return } } else { { return } })

test/expr/unary/do_expr.swift

@@ -147,7 +147,7 @@ func testReturn1() -> Int {
     try throwsError()
   } catch {
     if .random() {
-      return 0 // expected-error {{cannot 'return' in 'do-catch' when used as expression}}
+      return 0 // expected-error {{cannot use 'return' to transfer control out of 'do-catch' expression}}
     }
     then 0
   }

test/expr/unary/if_expr.swift

@@ -340,7 +340,7 @@ struct TestFailableInit {
     let y = if x {
       0
     } else {
-      return nil // expected-error {{cannot 'return' in 'if' when used as expression}}
+      return nil // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
     }
     _ = y
   }
@@ -605,16 +605,16 @@ func returnBranches1() -> Int {
 
 func returnBranchVoid() {
   return if .random() { return } else { return () }
-  // expected-error@-1 2{{cannot 'return' in 'if' when used as expression}}
+  // expected-error@-1 2{{cannot use 'return' to transfer control out of 'if' expression}}
 }
 
 func returnBranchBinding() -> Int {
   let x = if .random() {
     // expected-warning@-1 {{constant 'x' inferred to have type 'Void', which may be unexpected}}
     // expected-note@-2 {{add an explicit type annotation to silence this warning}}
-    return 0 // expected-error {{cannot 'return' in 'if' when used as expression}}
+    return 0 // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   } else {
-    return 1 // expected-error {{cannot 'return' in 'if' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   }
   return x // expected-error {{cannot convert return expression of type 'Void' to return type 'Int'}}
 }
@@ -648,9 +648,9 @@ func returnBranches5() throws -> Int {
   let i = if .random() {
     // expected-warning@-1 {{constant 'i' inferred to have type 'Void', which may be unexpected}}
     // expected-note@-2 {{add an explicit type annotation to silence this warning}}
-    return 0 // expected-error {{cannot 'return' in 'if' when used as expression}}
+    return 0 // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   } else {
-    return 1 // expected-error {{cannot 'return' in 'if' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   }
   let j = if .random() {
     // expected-warning@-1 {{constant 'j' inferred to have type 'Void', which may be unexpected}}
@@ -702,15 +702,15 @@ func returnBranches6PoundIf2() -> Int {
 func returnBranches7() -> Int {
   let i = if .random() {
     print("hello")
-    return 0  // expected-error {{cannot 'return' in 'if' when used as expression}}
+    return 0  // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   } else {
     1
   }
   return i
 }
 
 func returnBranches8() -> Int {
-  let i = if .random() { return 1 } else { 0 }  // expected-error {{cannot 'return' in 'if' when used as expression}}
+  let i = if .random() { return 1 } else { 0 }  // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
   return i
 }
 
@@ -914,7 +914,7 @@ func break1() -> Int {
   switch true {
   case true:
     let j = if .random() {
-      break // expected-error {{cannot 'break' in 'if' when used as expression}}
+      break // expected-error {{cannot use 'break' to transfer control out of 'if' expression}}
     } else {
       0
     }
@@ -927,7 +927,7 @@ func break1() -> Int {
 func continue1() -> Int {
   for _ in 0 ... 5 {
     let i = if true { continue } else { 1 }
-    // expected-error@-1 {{cannot 'continue' in 'if' when used as expression}}
+    // expected-error@-1 {{cannot use 'continue' to transfer control out of 'if' expression}}
     return i
   }
 }
@@ -941,7 +941,7 @@ func return1() -> Int {
         while true {
           switch 0 {
           default:
-            return 0 // expected-error {{cannot 'return' in 'if' when used as expression}}
+            return 0 // expected-error {{cannot use 'return' to transfer control out of 'if' expression}}
           }
         }
       }

test/expr/unary/switch_expr.swift

@@ -400,7 +400,7 @@ struct TestFailableInit {
     case true:
       0
     case false:
-      return nil // expected-error {{cannot 'return' in 'switch' when used as expression}}
+      return nil // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
     }
     _ = y
   }
@@ -757,17 +757,17 @@ func returnBranches1() -> Int {
 
 func returnBranchVoid() {
   return switch Bool.random() { case true: return case false: return () }
-  // expected-error@-1 2{{cannot 'return' in 'switch' when used as expression}}
+  // expected-error@-1 2{{cannot use 'return' to transfer control out of 'switch' expression}}
 }
 
 func returnBranchBinding() -> Int {
   let x = switch Bool.random() {
     // expected-warning@-1 {{constant 'x' inferred to have type 'Void', which may be unexpected}}
     // expected-note@-2 {{add an explicit type annotation to silence this warning}}
   case true:
-    return 0 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 0 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   case false:
-    return 1 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   }
   return x // expected-error {{cannot convert return expression of type 'Void' to return type 'Int'}}
 }
@@ -807,9 +807,9 @@ func returnBranches5() -> Int {
     // expected-warning@-1 {{constant 'i' inferred to have type 'Void', which may be unexpected}}
     // expected-note@-2 {{add an explicit type annotation to silence this warning}}
   case true:
-    return 0 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 0 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   case false:
-    return 1 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   }
   return i // expected-error {{cannot convert return expression of type 'Void' to return type 'Int'}}
 }
@@ -861,7 +861,7 @@ func returnBranches7() -> Int {
   let i = switch Bool.random() {
   case true:
     print("hello")
-    return 0 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 0 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   case false:
     1
   }
@@ -871,7 +871,7 @@ func returnBranches7() -> Int {
 func returnBranches8() -> Int {
   let i = switch Bool.random() {
   case true:
-    return 1 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   case false:
     0
   }
@@ -1173,7 +1173,7 @@ func fallthrough2() -> Int {
     if .random() {
       fallthrough
     }
-    return 1 // expected-error {{cannot 'return' in 'switch' when used as expression}}
+    return 1 // expected-error {{cannot use 'return' to transfer control out of 'switch' expression}}
   case false:
     0
   }