[cfe] Cache the context type when we resolve a dot shorthand.

Using the type analyzer to cache a shorthand context type. This mechanism will be shared between the analyzer and the CFE.

There will be tests for this one the implementation strings through to this part. But otherwise, it's fairly straightforward logic.

Bug: #59758
Change-Id: I88ac8283d2901d7d141992ab5ab3a83e40be5912
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/410943
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

Author: kallentu

pkg/_fe_analyzer_shared/lib/src/type_inference/type_analyzer.dart

@@ -271,6 +271,9 @@ mixin TypeAnalyzer<
         TypeDeclarationType extends Object,
         TypeDeclaration extends Object>
     implements TypeAnalysisNullShortingInterface<Expression, SharedTypeView> {
+  /// Cached context types used to resolve dot shorthand heads.
+  final _dotShorthands = <SharedTypeSchemaView>[];
+
   TypeAnalyzerErrors<Node, Statement, Expression, Variable, SharedTypeView,
       Pattern, Error> get errors;
 
@@ -535,6 +538,17 @@ mixin TypeAnalyzer<
         : operations.typeToSchema(declaredType);
   }
 
+  /// Analyzes a dot shorthand.
+  /// Saves the [context] for when we resolve the dot shorthand head.
+  SharedTypeView analyzeDotShorthand(
+      Expression node, SharedTypeSchemaView context) {
+    _dotShorthands.add(context);
+    ExpressionTypeAnalysisResult analysisResult =
+        dispatchExpression(node, context);
+    _dotShorthands.removeLast();
+    return analysisResult.type;
+  }
+
   /// Analyzes an expression.  [node] is the expression to analyze, and
   /// [schema] is the type schema which should be used for type inference.
   ///
@@ -2146,6 +2160,9 @@ mixin TypeAnalyzer<
     required SharedTypeView type,
   });
 
+  /// Returns the most recently cached dot shorthand context type.
+  SharedTypeSchemaView getDotShorthandContext() => _dotShorthands.last;
+
   /// If the [element] is a map pattern entry, returns it.
   MapPatternEntry<Expression, Pattern>? getMapPatternEntry(Node element);
 

pkg/front_end/lib/src/type_inference/inference_visitor.dart

@@ -12107,8 +12107,11 @@ class InferenceVisitorImpl extends InferenceVisitorBase
   // Coverage-ignore(suite): Not run.
   ExpressionInferenceResult visitDotShorthand(
       DotShorthand node, DartType typeContext) {
-    // TODO(kallentu): Implementation needed for dot shorthands.
-    return _unhandledExpression(node, typeContext);
+    DartType rewrittenType = analyzeDotShorthand(
+            node.innerExpression, new SharedTypeSchemaView(typeContext))
+        .unwrapTypeView();
+    Expression rewrittenExpr = popRewrite() as Expression;
+    return new ExpressionInferenceResult(rewrittenType, rewrittenExpr);
   }
 
   // Coverage-ignore(suite): Not run.