swift-syntax doesn't give negative integer literals special treatment while the Swift compiler does.

[YOCKOW]

Description

As discussed in some threads ¹², negative numeric literals have special treatment in Swift.
However, swift-syntax seems not to reflect such feature.
For further details, see "Steps to Reproduce" section.

Steps to Reproduce

Swift compiler says -1 is an integer literal with negative flag:

% echo '_ = -1' | swiftc -dump-ast -    
(source_file "<stdin>"
  (top_level_code_decl range=[<stdin>:1:1 - line:1:6]
    (brace_stmt implicit range=[<stdin>:1:1 - line:1:6]
      (assign_expr type='()' location=<stdin>:1:3 range=[<stdin>:1:1 - line:1:6]
        (discard_assignment_expr type='@lvalue Int' location=<stdin>:1:1 range=[<stdin>:1:1 - line:1:1])
        (integer_literal_expr type='Int' location=<stdin>:1:5 range=[<stdin>:1:5 - line:1:6] negative value=1 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**)))))

Meanwhile, swift-parser-cli says '-1' is a prefix operator '-' and its operand expression(an integer literal 1):

% echo '_ = -1' | swift-parser-cli print-tree
SourceFileSyntax
├─statements: CodeBlockItemListSyntax
│ ╰─[0]: CodeBlockItemSyntax
│   ╰─item: SequenceExprSyntax
│     ╰─elements: ExprListSyntax
│       ├─[0]: DiscardAssignmentExprSyntax
│       │ ╰─wildcard: wildcard
│       ├─[1]: AssignmentExprSyntax
│       │ ╰─equal: equal
│       ╰─[2]: PrefixOperatorExprSyntax
│         ├─operator: prefixOperator("-")
│         ╰─expression: IntegerLiteralExprSyntax
│           ╰─literal: integerLiteral("1")
╰─endOfFileToken: endOfFile

Footnotes

1. https://forums.swift.org/t/amendment-se-0368-staticbigint/62992/12 ↩

2. https://forums.swift.org/t/expressiblebyintegerliteral-and-type-inference-and-macro/73698/2 ↩

[ahoppen]

Synced to Apple’s issue tracker as rdar://133430491

[ahoppen]

This behavior is intentional. In the compiler’s pipeline, ASTGen will handle the unification of the prefix - with the number literal into a single AST node. Clients of swift-syntax will need to apply the prefix - manually.