[cfe] Desugar BinaryPattern

Part of #49749

Change-Id: I98dd7d63c560eb4c48350c32826e51df1491d9d9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/271708
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -2616,19 +2616,32 @@ class BodyBuilder extends StackListenerImpl
     reportIfNotEnabled(
         libraryFeatures.patterns, token.charOffset, token.charCount);
     // ignore: unused_local_variable
-    Pattern left = toPattern(pop());
-    // ignore: unused_local_variable
     Pattern right = toPattern(pop());
+    // ignore: unused_local_variable
+    Pattern left = toPattern(pop());
     // TODO(johnniwinther): Create a binary pattern.
 
     String operator = token.lexeme;
-    BinaryPatternKind kind;
     switch (operator) {
       case '&':
-        kind = BinaryPatternKind.and;
+        push(new AndPattern(left, right, token.charOffset));
         break;
       case '|':
-        kind = BinaryPatternKind.or;
+        Map<String, VariableDeclaration> leftVariablesByName = {
+          for (VariableDeclaration leftVariable in left.declaredVariables)
+            leftVariable.name!: leftVariable
+        };
+        if (!leftVariablesByName.keys.toSet().containsAll(
+                right.declaredVariables.map((variable) => variable.name!)) &&
+            leftVariablesByName.length == right.declaredVariables.length) {
+          // TODO(cstefantsova): Report a compile-time error.
+        }
+        push(new OrPattern(left, right, token.charOffset,
+            orPatternJointVariables: [
+              for (VariableDeclaration leftVariable in left.declaredVariables)
+                forest.createVariableDeclaration(
+                    leftVariable.fileOffset, leftVariable.name)
+            ]));
         break;
       default:
         internalProblem(
@@ -2637,7 +2650,6 @@ class BodyBuilder extends StackListenerImpl
             token.charOffset,
             uri);
     }
-    push(new BinaryPattern(left, kind, right, token.charOffset));
   }
 
   void doBinaryExpression(Token token) {

pkg/front_end/lib/src/fasta/kernel/forest.dart

@@ -413,8 +413,11 @@ class Forest {
   /// [fileOffset]. The [condition] is the expression preceding the question
   /// mark. The [thenExpression] is the expression following the question mark.
   /// The [elseExpression] is the expression following the colon.
-  Expression createConditionalExpression(int fileOffset, Expression condition,
-      Expression thenExpression, Expression elseExpression) {
+  ConditionalExpression createConditionalExpression(
+      int fileOffset,
+      Expression condition,
+      Expression thenExpression,
+      Expression elseExpression) {
     return new ConditionalExpression(
         condition, thenExpression, elseExpression, const UnknownType())
       ..fileOffset = fileOffset;