[analyzer] Fix dead code reporting in property access and is/as.

The way dead code detection works in the analyzer is that at various
ad hoc times during the process of resolution (typically before
visiting an expression or statement), the `ResolverVisitor` calls
`checkUnreachableNode`, which asks flow analysis whether the current
point in execution is reachable, and if it isn't, arranges for an
unreachable code warning to be produced.

This wasn't working for property extractions, type casts, and type
tests because there's no subexpression whose execution follows the
subexpression that returns `Never`, so `checkUnreachableNode` wasn't
getting called.

The fix is simple; just add some calls to `checkUnreachableNode` to
cover the RHS of a property access, type cast, or type test.

Note that property accesses in the analyzer can be represented either
as `PrefixedIdentifier` or `PropertyAccess`, so the property access
fix had to be done in two places (and accordingly there are two tests
for it).

Fixes #60247.

Bug: #60247
Change-Id: I49e739784f629b77443ce6d31e67809f48de75be
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/413521
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>
Auto-Submit: Paul Berry <[email protected]>

Author: stereotype441

pkg/analyzer/lib/src/dart/resolver/prefixed_identifier_resolver.dart

@@ -29,6 +29,7 @@ class PrefixedIdentifierResolver {
   }) {
     _resolver.analyzeExpression(node.prefix, _resolver.operations.unknownType);
     _resolver.popRewrite();
+    _resolver.checkUnreachableNode(node.identifier);
 
     var prefixElement = node.prefix.element;
     if (prefixElement is! PrefixElement2) {

pkg/analyzer/lib/src/generated/resolver.dart

@@ -1822,6 +1822,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
         node.expression, SharedTypeSchemaView(UnknownInferredType.instance));
     popRewrite();
 
+    checkUnreachableNode(node.type);
     node.type.accept(this);
 
     typeAnalyzer.visitAsExpression(node);
@@ -3070,6 +3071,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
         node.expression, SharedTypeSchemaView(UnknownInferredType.instance));
     popRewrite();
 
+    checkUnreachableNode(node.type);
     node.type.accept(this);
 
     typeAnalyzer.visitIsExpression(node);
@@ -3455,6 +3457,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
       popRewrite();
     }
 
+    checkUnreachableNode(node.propertyName);
     _resolvePropertyAccessRhs(node, contextType);
     inferenceLogWriter?.exitExpression(node);
   }

pkg/analyzer/test/src/dart/resolution/extension_method_test.dart

@@ -1044,6 +1044,7 @@ extension E on Never {
 }
 
 f(Never a) {
+  // ignore: dead_code
   a.foo;
 }
 ''');

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

@@ -17,6 +17,16 @@ main() {
 @reflectiveTest
 class DeadCodeTest extends PubPackageResolutionTest
     with DeadCodeTestCases_Language212 {
+  test_asExpression_type() async {
+    await assertErrorsInCode(r'''
+Never doNotReturn() => throw 0;
+
+test() => doNotReturn() as int;
+''', [
+      error(WarningCode.DEAD_CODE, 60, 4),
+    ]);
+  }
+
   test_deadBlock_conditionalElse_recordPropertyAccess() async {
     await assertErrorsInCode(r'''
 void f(({int x, int y}) p) {
@@ -157,6 +167,17 @@ void f(int a) {
     ]);
   }
 
+  test_isExpression_type() async {
+    await assertErrorsInCode(r'''
+Never doNotReturn() => throw 0;
+
+// ignore: unnecessary_type_check_true
+test() => doNotReturn() is int;
+''', [
+      error(WarningCode.DEAD_CODE, 99, 4),
+    ]);
+  }
+
   test_localFunction_wildcard() async {
     await assertErrorsInCode(r'''
 void f() {
@@ -194,6 +215,26 @@ void f(Object x) {
       error(WarningCode.DEAD_CODE, 84, 2),
     ]);
   }
+
+  test_prefixedIdentifier_identifier() async {
+    await assertErrorsInCode(r'''
+Never get doNotReturn => throw 0;
+
+test() => doNotReturn.hashCode;
+''', [
+      error(WarningCode.DEAD_CODE, 57, 9),
+    ]);
+  }
+
+  test_propertyAccess_property() async {
+    await assertErrorsInCode(r'''
+Never doNotReturn() => throw 0;
+
+test() => doNotReturn().hashCode;
+''', [
+      error(WarningCode.DEAD_CODE, 57, 9),
+    ]);
+  }
 }
 
 @reflectiveTest

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

@@ -889,6 +889,7 @@ PrefixExpression
   test_propertyAccess_never_read() async {
     await assertNoErrorsInCode(r'''
 void f(Never x) {
+  // ignore: dead_code
   x.foo;
 }
 ''');
@@ -916,6 +917,7 @@ PrefixedIdentifier
   test_propertyAccess_never_read_hashCode() async {
     await assertNoErrorsInCode(r'''
 void f(Never x) {
+  // ignore: dead_code
   x.hashCode;
 }
 ''');
@@ -987,6 +989,7 @@ AssignmentExpression
   test_propertyAccess_never_tearOff_toString() async {
     await assertNoErrorsInCode(r'''
 void f(Never x) {
+  // ignore: dead_code
   x.toString;
 }
 ''');
@@ -1142,6 +1145,7 @@ PrefixedIdentifier
   test_propertyAccess_toString() async {
     await assertNoErrorsInCode(r'''
 void f() {
+  // ignore: dead_code
   (throw '').toString;
 }
 ''');
@@ -1171,6 +1175,7 @@ PropertyAccess
   test_throw_getter_hashCode() async {
     await assertNoErrorsInCode(r'''
 void f() {
+  // ignore: dead_code
   (throw '').hashCode;
 }
 ''');