analyzer: expose canBeConst and computeConstantValue as public API

Work towards #50986

These utilities are used by a handful of lint rules, and the analysis
server, which makes me think they could be offered as public API.

Change-Id: I12415c2b86ca6fb96b03def4a304da73c6fb4cae
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430300
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: srawlins

pkg/analysis_server/lib/src/computer/computer_color.dart

@@ -9,7 +9,6 @@ import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/constant/value.dart' show GenericState;
-import 'package:analyzer/src/lint/constants.dart';
 import 'package:analyzer/src/utilities/extensions/flutter.dart';
 import 'package:collection/collection.dart';
 import 'package:path/path.dart' as path;
@@ -51,8 +50,12 @@ class ColorComputer {
 
     // Try to evaluate the constant target.
     var colorConstResult = target.computeConstantValue();
-    var colorConst = colorConstResult.value;
-    if (colorConstResult.errors.isNotEmpty || colorConst == null) return false;
+    var colorConst = colorConstResult?.value;
+    if (colorConstResult == null ||
+        colorConstResult.diagnostics.isNotEmpty ||
+        colorConst == null) {
+      return false;
+    }
 
     // If we want a specific member or swatch index, read that.
     if (memberName != null) {

pkg/analysis_server/lib/src/lsp/handlers/custom/editable_arguments/handler_editable_arguments.dart

@@ -16,7 +16,6 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
-import 'package:analyzer/src/lint/constants.dart';
 
 /// Information about the values for a parameter/argument.
 typedef _Values = ({DartObject? parameterValue, DartObject? argumentValue});
@@ -147,7 +146,7 @@ class EditableArgumentsHandler
     Expression? argumentExpression,
   ) {
     var parameterValue = parameter.computeConstantValue();
-    var argumentValue = argumentExpression?.computeConstantValue().value;
+    var argumentValue = argumentExpression?.computeConstantValue()?.value;
 
     return (parameterValue: parameterValue, argumentValue: argumentValue);
   }

pkg/analysis_server/lib/src/services/correction/dart/add_const.dart

@@ -9,7 +9,6 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/source/source_range.dart';
-import 'package:analyzer/src/lint/constants.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/change_builder/change_builder_dart.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';

pkg/analysis_server/lib/src/services/correction/dart/replace_with_decorated_box.dart

@@ -7,7 +7,6 @@ import 'package:analysis_server_plugin/edit/dart/correction_producer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/error.dart';
-import 'package:analyzer/src/lint/constants.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 import 'package:analyzer_plugin/utilities/range_factory.dart';

pkg/analyzer/api.txt

@@ -1058,12 +1058,14 @@ package:analyzer/dart/ast/ast.dart:
     exportKeyword (getter: Token)
     libraryExport (getter: LibraryExport?, experimental)
   Expression (class extends Object implements CollectionElement):
+    canBeConst (getter: bool)
     correspondingParameter (getter: FormalParameterElement?, experimental)
     inConstantContext (getter: bool)
     isAssignable (getter: bool)
     precedence (getter: Precedence)
     staticType (getter: DartType?)
     unParenthesized (getter: Expression)
+    computeConstantValue (method: AttemptedConstantEvaluationResult? Function())
   ExpressionFunctionBody (class extends Object implements FunctionBody):
     expression (getter: Expression)
     functionDefinition (getter: Token)
@@ -5106,6 +5108,10 @@ package:analyzer/src/dart/analysis/experiments_impl.dart:
     status (getter: FeatureStatus)
     stringForValue (method: String Function(bool))
     toString (method: String Function())
+package:analyzer/src/dart/ast/ast.dart:
+  AttemptedConstantEvaluationResult (class extends Object):
+    diagnostics (getter: List<Diagnostic>)
+    value (getter: DartObject?)
 package:analyzer/src/dart/constant/evaluation.dart:
   ConstantEvaluationTarget (class extends Object):
     new (constructor: ConstantEvaluationTarget Function())

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -19,21 +19,31 @@ import 'package:analyzer/dart/ast/doc_comment.dart';
 import 'package:analyzer/dart/ast/precedence.dart';
 import 'package:analyzer/dart/ast/syntactic_entity.dart';
 import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/scope.dart';
 import 'package:analyzer/dart/element/type.dart';
+import 'package:analyzer/diagnostic/diagnostic.dart';
+import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/source/line_info.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
 import 'package:analyzer/src/dart/ast/to_source_visitor.dart';
+import 'package:analyzer/src/dart/ast/token.dart';
+import 'package:analyzer/src/dart/constant/compute.dart';
+import 'package:analyzer/src/dart/constant/evaluation.dart';
+import 'package:analyzer/src/dart/constant/utilities.dart';
+import 'package:analyzer/src/dart/constant/value.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_schema.dart';
 import 'package:analyzer/src/dart/resolver/body_inference_context.dart';
 import 'package:analyzer/src/dart/resolver/typed_literal_resolver.dart';
+import 'package:analyzer/src/error/codes.g.dart';
 import 'package:analyzer/src/fasta/token_utils.dart' as util show findPrevious;
 import 'package:analyzer/src/generated/inference_log.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
+import 'package:analyzer/src/lint/constants.dart';
 import 'package:analyzer/src/utilities/extensions/object.dart';
 import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
@@ -1865,6 +1875,21 @@ abstract class AstVisitor<R> {
   R? visitYieldStatement(YieldStatement node);
 }
 
+/// The result of attempting to evaluate an expression as a constant.
+@AnalyzerPublicApi(message: 'exported by lib/dart/ast/ast.dart')
+final class AttemptedConstantEvaluationResult {
+  /// The value of the expression, or `null` if has [diagnostics].
+  ///
+  /// If evaluating a constant expression yields diagnostics, then the value of
+  /// the constant expression cannot be calculated.
+  final DartObject? value;
+
+  /// The diagnostics reported during the evaluation.
+  final List<Diagnostic> diagnostics;
+
+  AttemptedConstantEvaluationResult._(this.value, this.diagnostics);
+}
+
 /// The augmented expression.
 ///
 /// It is created only inside an augmentation.
@@ -8007,6 +8032,12 @@ final class ExportDirectiveImpl extends NamespaceDirectiveImpl
 ///      | [ThrowExpression]
 @AnalyzerPublicApi(message: 'exported by lib/dart/ast/ast.dart')
 abstract final class Expression implements CollectionElement {
+  /// Whether it would be valid for this expression to have a `const` keyword.
+  ///
+  /// Note that this method can cause constant evaluation to occur, which can be
+  /// computationally expensive.
+  bool get canBeConst;
+
   /// The parameter element representing the parameter to which the value of
   /// this expression is bound.
   ///
@@ -8064,6 +8095,14 @@ abstract final class Expression implements CollectionElement {
   /// unwrapping the expression inside the parentheses. Otherwise, returns this
   /// expression.
   Expression get unParenthesized;
+
+  /// Computes the constant value of this expression, if it has one.
+  ///
+  /// Returns a [AttemptedConstantEvaluationResult], containing both the computed
+  /// constant value, and a list of errors that occurred during the computation.
+  ///
+  /// Returns `null` if this expression is not a constant expression.
+  AttemptedConstantEvaluationResult? computeConstantValue();
 }
 
 /// A function body consisting of a single expression.
@@ -8215,6 +8254,9 @@ sealed class ExpressionImpl extends AstNodeImpl
     implements CollectionElementImpl, Expression {
   TypeImpl? _staticType;
 
+  @override
+  bool get canBeConst => false;
+
   @experimental
   @override
   FormalParameterElementMixin? get correspondingParameter {
@@ -8264,6 +8306,53 @@ sealed class ExpressionImpl extends AstNodeImpl
   @override
   ExpressionImpl get unParenthesized => this;
 
+  @override
+  AttemptedConstantEvaluationResult? computeConstantValue() {
+    var unitNode = thisOrAncestorOfType<CompilationUnitImpl>();
+    var unitFragment = unitNode?.declaredFragment;
+    if (unitFragment == null) {
+      throw ArgumentError('This AST structure has not yet been resolved.');
+    }
+
+    var libraryElement = unitFragment.element;
+    var declaredVariables = libraryElement.session.declaredVariables;
+
+    var evaluationEngine = ConstantEvaluationEngine(
+      declaredVariables: declaredVariables,
+      configuration: ConstantEvaluationConfiguration(),
+    );
+
+    var dependencies = <ConstantEvaluationTarget>[];
+    accept(ReferenceFinder(dependencies.add));
+
+    computeConstants(
+      declaredVariables: declaredVariables,
+      constants: dependencies,
+      featureSet: libraryElement.featureSet,
+      configuration: ConstantEvaluationConfiguration(),
+    );
+
+    var errorListener = RecordingErrorListener();
+    var visitor = ConstantVisitor(
+      evaluationEngine,
+      libraryElement,
+      ErrorReporter(errorListener, unitFragment.source),
+    );
+
+    var constant = visitor.evaluateAndReportInvalidConstant(this);
+    var isInvalidConstant = errorListener.errors.any(
+      (e) => e.errorCode == CompileTimeErrorCode.INVALID_CONSTANT,
+    );
+    if (isInvalidConstant) {
+      return null;
+    }
+
+    return AttemptedConstantEvaluationResult._(
+      constant is DartObjectImpl ? constant : null,
+      errorListener.errors,
+    );
+  }
+
   /// Returns the [AstNode] that puts node into the constant context, and
   /// the explicit `const` keyword of that node. The keyword might be absent
   /// if the constness is implicit.
@@ -14057,6 +14146,25 @@ final class InstanceCreationExpressionImpl extends ExpressionImpl
     return constructorName.beginToken;
   }
 
+  @override
+  bool get canBeConst {
+    var element = constructorName.element;
+    if (element == null || !element.isConst) return false;
+
+    // Ensure that dependencies (e.g. default parameter values) are computed.
+    element.baseElement.computeConstantDependencies();
+
+    // Verify that the evaluation of the constructor would not produce an
+    // exception.
+    var oldKeyword = keyword;
+    try {
+      keyword = KeywordToken(Keyword.CONST, offset);
+      return !hasConstantVerifierError;
+    } finally {
+      keyword = oldKeyword;
+    }
+  }
+
   @generated
   @override
   ConstructorNameImpl get constructorName => _constructorName;
@@ -24540,6 +24648,17 @@ sealed class TypedLiteralImpl extends LiteralImpl implements TypedLiteral {
     _becomeParentOf(_typeArguments);
   }
 
+  @override
+  bool get canBeConst {
+    var oldKeyword = constKeyword;
+    try {
+      constKeyword = KeywordToken(Keyword.CONST, offset);
+      return !hasConstantVerifierError;
+    } finally {
+      constKeyword = oldKeyword;
+    }
+  }
+
   @override
   bool get isConst {
     return constKeyword != null || inConstantContext;

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

@@ -33,7 +33,6 @@ import 'package:analyzer/src/error/error_handler_verifier.dart';
 import 'package:analyzer/src/error/must_call_super_verifier.dart';
 import 'package:analyzer/src/error/null_safe_api_verifier.dart';
 import 'package:analyzer/src/error/widget_preview_verifier.dart';
-import 'package:analyzer/src/lint/constants.dart';
 import 'package:analyzer/src/utilities/extensions/ast.dart';
 import 'package:analyzer/src/utilities/extensions/element.dart';
 import 'package:analyzer/src/workspace/workspace.dart';
@@ -873,7 +872,7 @@ class BestPracticesVerifier extends RecursiveAstVisitor<void> {
     var alreadySeen = <DartObject>{};
     for (var expression in expressions) {
       var constEvaluation = expression.computeConstantValue();
-      if (constEvaluation.errors.isEmpty) {
+      if (constEvaluation != null && constEvaluation.diagnostics.isEmpty) {
         var value = constEvaluation.value;
         if (value != null && !alreadySeen.add(value)) {
           var errorCode =