With ...obvious... lints, treat dynamic like other types

The lints `omit_obvious_local_variable_types` and
`specify_nonobvious_local_variable_types` have previously treated
the type `dynamic` in a special way. This CL changes these lints such
that they treat `dynamic` as the type annotation of a local variable
just like any other type used in the same situation.

This means that `dynamic d = 1;` will no longer be linted by
`specify_nonobvious_local_variable_types` (note that the type of
`1` is currently considered non-obvious), but
`dynamic d = 1 as dynamic;` will now be linted by
`omit_obvious_local_variable_types`.

Change-Id: Ib04b38c2aad8512839e90c29e4021487ad853e7e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381500
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Erik Ernst <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: eernstg

pkg/linter/lib/src/rules/omit_obvious_local_variable_types.dart

@@ -136,9 +136,7 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   void _visitVariableDeclarationList(VariableDeclarationList node) {
     var staticType = node.type?.type;
-    if (staticType == null ||
-        staticType is DynamicType ||
-        staticType.isDartCoreNull) {
+    if (staticType == null || staticType.isDartCoreNull) {
       return;
     }
     for (var child in node.variables) {

pkg/linter/lib/src/rules/specify_nonobvious_local_variable_types.dart

@@ -184,9 +184,7 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   void _visitVariableDeclarationList(VariableDeclarationList node) {
     var staticType = node.type?.type;
-    if (staticType != null &&
-        staticType is! DynamicType &&
-        !staticType.isDartCoreNull) {
+    if (staticType != null && !staticType.isDartCoreNull) {
       return;
     }
     bool aDeclaredTypeIsNeeded = false;

pkg/linter/test/rules/omit_obvious_local_variable_types_test.dart

@@ -29,6 +29,18 @@ num n = 1;
     ]);
   }
 
+  test_as_dynamic() async {
+    await assertDiagnostics(r'''
+f() {
+  dynamic i = n as dynamic;
+}
+
+num n = 1;
+''', [
+      lint(8, 7),
+    ]);
+  }
+
   test_cascade() async {
     await assertDiagnostics(r'''
 f() {

pkg/linter/test/rules/specify_nonobvious_local_variable_types_test.dart

@@ -17,6 +17,22 @@ class SpecifyNonObviousLocalVariableTypesTest extends LintRuleTest {
   @override
   String get lintRule => 'specify_nonobvious_local_variable_types';
 
+  test_as() async {
+    await assertNoDiagnostics(r'''
+f() {
+  var d = 1 as num;
+}
+''');
+  }
+
+  test_as_dynamic() async {
+    await assertNoDiagnostics(r'''
+f() {
+  var d = 1 as dynamic;
+}
+''');
+  }
+
   test_cascade() async {
     await assertNoDiagnostics(r'''
 f() {