unified: Fix issue with '_' as an assignment target

Author: asgerf

unified/extractor/src/languages/swift/swift.rs

@@ -267,8 +267,11 @@ fn translation_rules() -> Vec<Rule<SwiftContext>> {
         // `reduce(0, +)`), are both `declReferenceExpr`; its `baseName` is the
         // referenced identifier / operator symbol.
         rule!((declReferenceExpr baseName: @name) => (name_expr identifier: (identifier #{name}))),
-        // A discard `_` used as the target of an assignment becomes an `ignore_pattern`.
-        rule!((discardAssignmentExpr wildcard: @@w) => (ignore_pattern #{w})),
+        // A discard `_` used as the target of an assignment becomes a `builtin_expr` because the LHS of a
+        // tuple-assignment such as `(foo.x, _) = ...` can't contain a mix of patterns and exprs. So we consistently
+        // use exprs.
+        rule!((discardAssignmentExpr wildcard: @@w) where ctx.in_pattern => (ignore_pattern #{w})),
+        rule!((discardAssignmentExpr wildcard: @@w) => (builtin_expr #{w})),
         // A generic specialization in expression position (`C<Foo>`,
         // `Array<Int>`) is represented by swift-syntax as a
         // `genericSpecializationExpr`. When used as a call target

unified/extractor/tests/corpus/swift/operators/unresolved-operator-sequence-with-casts.output

@@ -117,7 +117,7 @@ top_level
               stmt:
                 unresolved_operator_sequence
                   element:
-                    ignore_pattern "_"
+                    builtin_expr "_"
                     infix_operator "="
                     name_expr
                       identifier: identifier "a"
@@ -128,7 +128,7 @@ top_level
                       identifier: identifier "b"
                 unresolved_operator_sequence
                   element:
-                    ignore_pattern "_"
+                    builtin_expr "_"
                     infix_operator "="
                     name_expr
                       identifier: identifier "a"

unified/extractor/tests/corpus/swift/operators/unresolved-operator-sequence.output

@@ -90,7 +90,7 @@ top_level
               stmt:
                 unresolved_operator_sequence
                   element:
-                    ignore_pattern "_"
+                    builtin_expr "_"
                     infix_operator "="
                     name_expr
                       identifier: identifier "a"

unified/extractor/tests/corpus/swift/variables/tuple-assignment.output

@@ -0,0 +1,126 @@
+(x, _) = (1, 2)
+(foo.x, _) = (1, 2)
+
+---
+
+sourceFile
+  endOfFileToken: endOfFile
+  statements:
+    codeBlockItem
+      item:
+        infixOperatorExpr
+          operator:
+            assignmentExpr
+              equal: =
+          leftOperand:
+            tupleExpr
+              leftParen: (
+              rightParen: )
+              elements:
+                labeledExpr
+                  expression:
+                    declReferenceExpr
+                      baseName: identifier "x"
+                  trailingComma: ,
+                labeledExpr
+                  expression:
+                    discardAssignmentExpr
+                      wildcard: _
+          rightOperand:
+            tupleExpr
+              leftParen: (
+              rightParen: )
+              elements:
+                labeledExpr
+                  expression:
+                    integerLiteralExpr
+                      literal: integerLiteral "1"
+                  trailingComma: ,
+                labeledExpr
+                  expression:
+                    integerLiteralExpr
+                      literal: integerLiteral "2"
+    codeBlockItem
+      item:
+        infixOperatorExpr
+          operator:
+            assignmentExpr
+              equal: =
+          leftOperand:
+            tupleExpr
+              leftParen: (
+              rightParen: )
+              elements:
+                labeledExpr
+                  expression:
+                    memberAccessExpr
+                      period: .
+                      declName:
+                        declReferenceExpr
+                          baseName: identifier "x"
+                      base:
+                        declReferenceExpr
+                          baseName: identifier "foo"
+                  trailingComma: ,
+                labeledExpr
+                  expression:
+                    discardAssignmentExpr
+                      wildcard: _
+          rightOperand:
+            tupleExpr
+              leftParen: (
+              rightParen: )
+              elements:
+                labeledExpr
+                  expression:
+                    integerLiteralExpr
+                      literal: integerLiteral "1"
+                  trailingComma: ,
+                labeledExpr
+                  expression:
+                    integerLiteralExpr
+                      literal: integerLiteral "2"
+
+---
+
+top_level
+  body:
+    block
+      stmt:
+        assign_expr
+          target:
+            tuple_expr
+              element:
+                argument
+                  value:
+                    name_expr
+                      identifier: identifier "x"
+                argument
+                  value: builtin_expr "_"
+          value:
+            tuple_expr
+              element:
+                argument
+                  value: int_literal "1"
+                argument
+                  value: int_literal "2"
+        assign_expr
+          target:
+            tuple_expr
+              element:
+                argument
+                  value:
+                    member_access_expr
+                      base:
+                        name_expr
+                          identifier: identifier "foo"
+                      member: identifier "x"
+                argument
+                  value: builtin_expr "_"
+          value:
+            tuple_expr
+              element:
+                argument
+                  value: int_literal "1"
+                argument
+                  value: int_literal "2"

unified/extractor/tests/corpus/swift/variables/tuple-assignment.swift

@@ -0,0 +1,2 @@
+(x, _) = (1, 2)
+(foo.x, _) = (1, 2)