[cfe] Provide pre-desugaring node to flow analysis to fix promotion

Part of https://github.com/dart-lang/sdk/issues/49749

Change-Id: I2a70518975c809f28f0d0f72f7365492ca7d6e83
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287601
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

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

@@ -1744,7 +1744,7 @@ mixin TypeAnalyzer<
           handleNoGuard(node, i);
           // Stack: (Expression, i * ExpressionCase, Pattern, Expression)
         }
-        handleCaseHead(node, caseIndex: i, subIndex: 0);
+        handleCaseHead(node, memberInfo.head, caseIndex: i, subIndex: 0);
       } else {
         handleDefault(node, caseIndex: i, subIndex: 0);
       }
@@ -1843,7 +1843,9 @@ mixin TypeAnalyzer<
           } else {
             handleNoGuard(node, caseIndex);
           }
-          handleCaseHead(node, caseIndex: caseIndex, subIndex: headIndex);
+          head = handleCaseHead(node, head,
+              caseIndex: caseIndex, subIndex: headIndex);
+          guard = head.guard;
         } else {
           hasDefault = true;
           handleDefault(node, caseIndex: caseIndex, subIndex: headIndex);
@@ -2136,11 +2138,15 @@ mixin TypeAnalyzer<
   /// Called after visiting a single `case` clause, consisting of a pattern and
   /// an optional guard.
   ///
-  /// [node] is the enclosing switch statement or switch expression and
+  /// [node] is the enclosing switch statement or switch expression,
+  /// [head] is the head to be handled, and
   /// [caseIndex] is the index of the `case` clause.
   ///
+  /// Returns the updated case head.
+  ///
   /// Stack effect: pops (Pattern, Expression) and pushes (CaseHead).
-  void handleCaseHead(Node node,
+  CaseHeadOrDefaultInfo<Node, Expression, Variable> handleCaseHead(
+      Node node, CaseHeadOrDefaultInfo<Node, Expression, Variable> head,
       {required int caseIndex, required int subIndex});
 
   /// Called after visiting a `default` clause.

pkg/_fe_analyzer_shared/test/mini_ast.dart

@@ -3727,7 +3727,8 @@ class _MiniAstTypeAnalyzer
   }
 
   @override
-  void handleCaseHead(Node node,
+  CaseHeadOrDefaultInfo<Node, Expression, Var> handleCaseHead(
+      Node node, CaseHeadOrDefaultInfo<Node, Expression, Var> head,
       {required int caseIndex, required int subIndex}) {
     Iterable<Var> variables = [];
     if (node is _SwitchExpression) {
@@ -3748,6 +3749,8 @@ class _MiniAstTypeAnalyzer
     _irBuilder.apply(
         'head', [Kind.pattern, Kind.expression, Kind.variables], Kind.caseHead,
         location: node.location);
+
+    return head;
   }
 
   void handleDeclaredVariablePattern(covariant _VariablePattern node,

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

@@ -1085,8 +1085,9 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
       AstNode node, int caseIndex, Iterable<PromotableElement> variables) {}
 
   @override
-  void handleCaseHead(
+  CaseHeadOrDefaultInfo<AstNode, Expression, PromotableElement> handleCaseHead(
-    covariant AstNodeImpl node, {
+    covariant AstNodeImpl node,
+    CaseHeadOrDefaultInfo<AstNode, Expression, PromotableElement> head, {
     required int caseIndex,
     required int subIndex,
   }) {
@@ -1101,6 +1102,8 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
       legacySwitchExhaustiveness
           ?.visitSwitchExpressionCase(node.cases[caseIndex]);
     }
+
+    return head;
   }
 
   @override

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

@@ -9864,10 +9864,14 @@ class InferenceVisitorImpl extends InferenceVisitorBase
   }
 
   @override
-  void handleCaseHead(
+  CaseHeadOrDefaultInfo<TreeNode, Expression, VariableDeclaration>
-      covariant /* SwitchStatement | SwitchExpression */ Object node,
+      handleCaseHead(
-      {required int caseIndex,
+          covariant /* SwitchStatement | SwitchExpression */ Object node,
-      required int subIndex}) {
+          CaseHeadOrDefaultInfo<TreeNode, Expression, VariableDeclaration> head,
+          {required int caseIndex,
+          required int subIndex}) {
+    CaseHeadOrDefaultInfo<TreeNode, Expression, VariableDeclaration> result =
+        head;
     int? stackBase;
     assert(checkStackBase(node as TreeNode, stackBase = stackHeight - 2));
 
@@ -9919,6 +9923,12 @@ class InferenceVisitorImpl extends InferenceVisitorBase
             !identical(guardRewrite, patternGuard.guard)) {
           patternGuard.guard = (guardRewrite as Expression)
             ..parent = patternGuard;
+
+          result = new CaseHeadOrDefaultInfo(
+            pattern: head.pattern,
+            guard: patternGuard.guard,
+            variables: head.variables,
+          );
         }
         Object? rewrite = popRewrite();
         if (!identical(rewrite, patternGuard.pattern)) {
@@ -9972,6 +9982,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
           hasGuard: patternGuard.guard != null,
           fileOffset: switchExpressionCase.fileOffset));
     }
+
+    return result;
   }
 
   @override

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+test(String? x) {
+  switch (x) {
+    case String? foobar? when foobar is Never:
+    case String? foobar when foobar != null:
+    case String? foobar! when foobar == "foobar":
+      return foobar.startsWith("foo"); // The static type of 'foobar' is expected to be the non-nullable 'String'.
+    default:
+      return null;
+  }
+}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.strong.expect

@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic {
+  #L1:
+  {
+    core::String? foobar;
+    core::String? foobar#1;
+    core::String? foobar#2;
+    final core::String? #0#0 = x;
+    dynamic #t1;
+    if((!(#0#0 == null) ?{core::bool} #0#0{core::String} is{ForNonNullableByDefault} core::String? && (let final dynamic #t2 = foobar = #0#0{core::String} in true) : false) && foobar{core::String} is{ForNonNullableByDefault} Never && (let final dynamic #t3 = #t1 = foobar in true) || #0#0 is{ForNonNullableByDefault} core::String? && (let final dynamic #t4 = foobar#1 = #0#0 in true) && !(foobar#1 == null) && (let final dynamic #t5 = #t1 = foobar#1 in true) || (let final dynamic #t6 = #0#0! in #0#0! is{ForNonNullableByDefault} core::String? && (let final dynamic #t7 = foobar#2 = #0#0! in true)) && foobar#2{core::String} =={core::String::==}{(core::Object) → core::bool} "foobar" && (let final dynamic #t8 = #t1 = foobar#2 in true)) {
+      core::String? foobar = #t1{core::String?};
+      {
+        return foobar{core::String}.{core::String::startsWith}("foo"){(core::Pattern, [core::int]) → core::bool};
+      }
+    }
+    else {
+      {
+        return null;
+      }
+    }
+  }
+}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.strong.transformed.expect

@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic {
+  #L1:
+  {
+    core::String? foobar;
+    core::String? foobar#1;
+    core::String? foobar#2;
+    final core::String? #0#0 = x;
+    dynamic #t1;
+    if((!(#0#0 == null) ?{core::bool} #0#0{core::String} is{ForNonNullableByDefault} core::String? && (let final core::String #t2 = foobar = #0#0{core::String} in true) : false) && foobar{core::String} is{ForNonNullableByDefault} Never && (let final core::String? #t3 = #t1 = foobar in true) || #0#0 is{ForNonNullableByDefault} core::String? && (let final core::String? #t4 = foobar#1 = #0#0 in true) && !(foobar#1 == null) && (let final core::String? #t5 = #t1 = foobar#1 in true) || (let final core::String? #t6 = #0#0! in #0#0! is{ForNonNullableByDefault} core::String? && (let final core::String? #t7 = foobar#2 = #0#0! in true)) && foobar#2{core::String} =={core::String::==}{(core::Object) → core::bool} "foobar" && (let final core::String? #t8 = #t1 = foobar#2 in true)) {
+      core::String? foobar = #t1{core::String?};
+      {
+        return foobar{core::String}.{core::String::startsWith}("foo"){(core::Pattern, [core::int]) → core::bool};
+      }
+    }
+    else {
+      {
+        return null;
+      }
+    }
+  }
+}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.textual_outline.expect

@@ -0,0 +1 @@
+test(String? x) {}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.textual_outline_modelled.expect

@@ -0,0 +1 @@
+test(String? x) {}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.weak.expect

@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic {
+  #L1:
+  {
+    core::String? foobar;
+    core::String? foobar#1;
+    core::String? foobar#2;
+    final core::String? #0#0 = x;
+    dynamic #t1;
+    if((!(#0#0 == null) ?{core::bool} #0#0{core::String} is{ForNonNullableByDefault} core::String? && (let final dynamic #t2 = foobar = #0#0{core::String} in true) : false) && foobar{core::String} is{ForNonNullableByDefault} Never && (let final dynamic #t3 = #t1 = foobar in true) || #0#0 is{ForNonNullableByDefault} core::String? && (let final dynamic #t4 = foobar#1 = #0#0 in true) && !(foobar#1 == null) && (let final dynamic #t5 = #t1 = foobar#1 in true) || (let final dynamic #t6 = #0#0! in #0#0! is{ForNonNullableByDefault} core::String? && (let final dynamic #t7 = foobar#2 = #0#0! in true)) && foobar#2{core::String} =={core::String::==}{(core::Object) → core::bool} "foobar" && (let final dynamic #t8 = #t1 = foobar#2 in true)) {
+      core::String? foobar = #t1{core::String?};
+      {
+        return foobar{core::String}.{core::String::startsWith}("foo"){(core::Pattern, [core::int]) → core::bool};
+      }
+    }
+    else {
+      {
+        return null;
+      }
+    }
+  }
+}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.weak.modular.expect

@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic {
+  #L1:
+  {
+    core::String? foobar;
+    core::String? foobar#1;
+    core::String? foobar#2;
+    final core::String? #0#0 = x;
+    dynamic #t1;
+    if((!(#0#0 == null) ?{core::bool} #0#0{core::String} is{ForNonNullableByDefault} core::String? && (let final dynamic #t2 = foobar = #0#0{core::String} in true) : false) && foobar{core::String} is{ForNonNullableByDefault} Never && (let final dynamic #t3 = #t1 = foobar in true) || #0#0 is{ForNonNullableByDefault} core::String? && (let final dynamic #t4 = foobar#1 = #0#0 in true) && !(foobar#1 == null) && (let final dynamic #t5 = #t1 = foobar#1 in true) || (let final dynamic #t6 = #0#0! in #0#0! is{ForNonNullableByDefault} core::String? && (let final dynamic #t7 = foobar#2 = #0#0! in true)) && foobar#2{core::String} =={core::String::==}{(core::Object) → core::bool} "foobar" && (let final dynamic #t8 = #t1 = foobar#2 in true)) {
+      core::String? foobar = #t1{core::String?};
+      {
+        return foobar{core::String}.{core::String::startsWith}("foo"){(core::Pattern, [core::int]) → core::bool};
+      }
+    }
+    else {
+      {
+        return null;
+      }
+    }
+  }
+}

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.weak.outline.expect

@@ -0,0 +1,6 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic
+  ;

pkg/front_end/testcases/patterns/promotions_in_switch_case_guards.dart.weak.transformed.expect

@@ -0,0 +1,25 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method test(core::String? x) → dynamic {
+  #L1:
+  {
+    core::String? foobar;
+    core::String? foobar#1;
+    core::String? foobar#2;
+    final core::String? #0#0 = x;
+    dynamic #t1;
+    if((!(#0#0 == null) ?{core::bool} #0#0{core::String} is{ForNonNullableByDefault} core::String? && (let final core::String #t2 = foobar = #0#0{core::String} in true) : false) && foobar{core::String} is{ForNonNullableByDefault} Never && (let final core::String? #t3 = #t1 = foobar in true) || #0#0 is{ForNonNullableByDefault} core::String? && (let final core::String? #t4 = foobar#1 = #0#0 in true) && !(foobar#1 == null) && (let final core::String? #t5 = #t1 = foobar#1 in true) || (let final core::String? #t6 = #0#0! in #0#0! is{ForNonNullableByDefault} core::String? && (let final core::String? #t7 = foobar#2 = #0#0! in true)) && foobar#2{core::String} =={core::String::==}{(core::Object) → core::bool} "foobar" && (let final core::String? #t8 = #t1 = foobar#2 in true)) {
+      core::String? foobar = #t1{core::String?};
+      {
+        return foobar{core::String}.{core::String::startsWith}("foo"){(core::Pattern, [core::int]) → core::bool};
+      }
+    }
+    else {
+      {
+        return null;
+      }
+    }
+  }
+}