[analyzer] Fix dead code range for do loop.

Prior to this change, a `do` loop such as this one:

    do {
      return;
    } while (true);

would be flagged with two DEAD_CODE warnings: one covering the text `}
while (true);` (which makes sense), and one covering the text `do {`
(which doesn't make sense at all, since the top of the `do` loop is
reachable).

Digging through the code and git history, I've found no good reason
for the DEAD_CODE warning at `do {` to exist. It looks like it was
added as part of a bug fix from an external contributor and not
spotted during code review
(https://dart-review.googlesource.com/c/sdk/+/266389).

With the unnecessary dead code range removed, some of the tests of the
analysis server's `remove_dead_code` fix become simpler (they don't
need to use an `errorFilter` to select which dead code range to act
on). Others become unnecessary (since they were verifying that
`remove_dead_code` properly handled the bogus dead code range). Others
simply needed their `errorFilter` changed to select the appropriate
dead code range.

Making this fix paves the way for improving the `remove_dead_code`
fix, which I want to do as part of shipping the `sound-flow-analysis`
feature.

Change-Id: Iee0bc187441bc4be76a8fa57198155dff3731bc8
Bug: #60438
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/423421
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/analysis_server/test/src/services/correction/fix/remove_dead_code_test.dart

@@ -117,75 +117,7 @@ void f(bool c) {
     print(c);
     return;
 }
-''', errorFilter: (error) => error.length == 4);
-  }
-
-  Future<void> test_doWhile_atDo() async {
-    await resolveTestCode('''
-void f(bool c) {
-  do {
-    print(c);
-    return;
-  } while (c);
-}
-''');
-    await assertHasFix('''
-void f(bool c) {
-    print(c);
-    return;
-}
-''', errorFilter: (err) => err.problemMessage.length == 4);
-  }
-
-  Future<void> test_doWhile_atDo_followed() async {
-    await resolveTestCode('''
-void f(bool c) {
-  do {
-    print(c);
-    return;
-  } while (c);
-  print('');
-}
 ''');
-    await assertHasFix('''
-void f(bool c) {
-    print(c);
-    return;
-  print('');
-}
-''', errorFilter: (err) => err.problemMessage.length == 4);
-  }
-
-  Future<void> test_doWhile_atDo_noBrackets() async {
-    await resolveTestCode('''
-void f(bool c) {
-  do
-    return;
-  while (c);
-}
-''');
-    await assertHasFix('''
-void f(bool c) {
-  return;
-}
-''', errorFilter: (err) => err.problemMessage.length == 2);
-  }
-
-  Future<void> test_doWhile_atDo_noBrackets_followed() async {
-    await resolveTestCode('''
-void f(bool c) {
-  do
-    return;
-  while (c);
-  print('');
-}
-''');
-    await assertHasFix('''
-void f(bool c) {
-  return;
-  print('');
-}
-''', errorFilter: (err) => err.problemMessage.length == 2);
   }
 
   Future<void> test_doWhile_atWhile() async {
@@ -202,7 +134,7 @@ void f(bool c) {
     print(c);
     return;
 }
-''', errorFilter: (err) => err.problemMessage.length == 12);
+''');
   }
 
   Future<void> test_doWhile_atWhile_noBrackets() async {
@@ -217,7 +149,7 @@ void f(bool c) {
 void f(bool c) {
   return;
 }
-''', errorFilter: (err) => err.problemMessage.length == 10);
+''');
   }
 
   Future<void> test_doWhile_break() async {
@@ -232,7 +164,7 @@ void f(bool c) {
   print('');
 }
 ''');
-    await assertNoFix(errorFilter: (error) => error.length == 4);
+    await assertNoFix();
   }
 
   Future<void> test_doWhile_break_doLabel() async {
@@ -248,7 +180,7 @@ void f(bool c) {
   print('');
 }
 ''');
-    await assertNoFix(errorFilter: (error) => error.length == 4);
+    await assertNoFix();
   }
 
   Future<void> test_doWhile_break_inner() async {
@@ -271,7 +203,7 @@ void f(bool c) {
     return;
   print('');
 }
-''', errorFilter: (error) => error.length == 4);
+''', errorFilter: (error) => error.length == 12);
   }
 
   Future<void> test_doWhile_break_outerDoLabel() async {
@@ -302,7 +234,7 @@ void f(bool c) {
   } while (c);
   print('');
 }
-''', errorFilter: (error) => error.length == 4);
+''', errorFilter: (error) => error.length == 12);
   }
 
   Future<void> test_doWhile_break_outerLabel() async {
@@ -329,7 +261,7 @@ void f(bool c) {
     print('');
   }
 }
-''', errorFilter: (error) => error.length == 4);
+''', errorFilter: (error) => error.length == 12);
   }
 
   Future<void> test_emptyStatement() async {

pkg/analyzer/lib/src/error/dead_code_verifier.dart

@@ -285,20 +285,12 @@ class NullSafetyDeadCodeVerifier {
         );
         offset = node.end;
       } else if (parent is DoStatement) {
-        var doOffset = parent.doKeyword.offset;
-        var doEnd = parent.doKeyword.end;
         var whileOffset = parent.whileKeyword.offset;
         var whileEnd = parent.semicolon.end;
         var body = parent.body;
         if (body is Block) {
-          doEnd = body.leftBracket.end;
           whileOffset = body.rightBracket.offset;
         }
-        _errorReporter.atOffset(
-          offset: doOffset,
-          length: doEnd - doOffset,
-          errorCode: WarningCode.DEAD_CODE,
-        );
         _errorReporter.atOffset(
           offset: whileOffset,
           length: whileEnd - whileOffset,

pkg/analyzer/test/src/diagnostics/dead_code_test.dart

@@ -950,10 +950,7 @@ void f(bool c) {
   } while (c);
 }
 ''',
-      [
-        error(WarningCode.DEAD_CODE, 19, 4),
-        error(WarningCode.DEAD_CODE, 52, 12),
-      ],
+      [error(WarningCode.DEAD_CODE, 52, 12)],
     );
   }
 
@@ -970,10 +967,7 @@ void f(bool c) {
   print('');
 }
 ''',
-      [
-        error(WarningCode.DEAD_CODE, 19, 4),
-        error(WarningCode.DEAD_CODE, 69, 12),
-      ],
+      [error(WarningCode.DEAD_CODE, 69, 12)],
     );
   }
 
@@ -991,10 +985,7 @@ void f(bool c) {
   print('');
 }
 ''',
-      [
-        error(WarningCode.DEAD_CODE, 28, 4),
-        error(WarningCode.DEAD_CODE, 85, 12),
-      ],
+      [error(WarningCode.DEAD_CODE, 85, 12)],
     );
   }
 
@@ -1012,7 +1003,6 @@ void f(bool c) {
 }
 ''',
       [
-        error(WarningCode.DEAD_CODE, 19, 4),
         error(WarningCode.DEAD_CODE, 73, 12),
         error(WarningCode.DEAD_CODE, 88, 10),
       ],
@@ -1037,7 +1027,6 @@ void f(bool c) {
 }
 ''',
       [
-        error(WarningCode.DEAD_CODE, 37, 4),
         error(WarningCode.DEAD_CODE, 104, 12),
         error(WarningCode.DEAD_CODE, 121, 38),
       ],
@@ -1060,7 +1049,6 @@ void f(bool c) {
 }
 ''',
       [
-        error(WarningCode.DEAD_CODE, 32, 4),
         error(WarningCode.DEAD_CODE, 98, 12),
         error(WarningCode.DEAD_CODE, 115, 14),
       ],
@@ -1079,7 +1067,6 @@ void f(bool c) {
 }
 ''',
       [
-        error(WarningCode.DEAD_CODE, 19, 4),
         error(WarningCode.DEAD_CODE, 52, 12),
         error(WarningCode.DEAD_CODE, 67, 11),
       ],