Macro assert_parse_tree 

macro_rules! assert_parse_tree {
    ($src:expr, $($tree:tt)+) => { ... };
    (@seq $parser:ident, Warn ( $code:expr ) $($rest:tt)*) => { ... };
    (@seq $parser:ident, Error ( $code:expr ) $($rest:tt)*) => { ... };
    (@seq $parser:ident, $kind:ident [ $($children:tt)+ ] $($rest:tt)*) => { ... };
    (@seq $parser:ident, $kind:ident ( $text:expr ) $($rest:tt)*) => { ... };
    (@seq $parser:ident, $kind:ident $($rest:tt)*) => { ... };
    (@seq $parser:ident, ...) => { ... };
    (@seq $parser:ident,) => { ... };
}

Macro to assert the structure and content of the parsed syntax tree from source code.

Purpose

assert_parse_tree! allows you to declaratively specify the expected abstract syntax tree (AST) shape and tokens produced by your parser for a given source code snippet. It recursively matches nodes by their kinds (SyntaxKind) and token text, verifying both the hierarchical structure and token lexemes precisely.

This macro is primarily useful in parser/unit tests where you want to:

• Assert nodes and their nested children are present in expected order.
• Assert leaf tokens have expected text content.
• Assert presence of parser errors and warnings at specific nodes.

Syntax Overview

assert_parse_tree!(
    "source code string",
    RootNodeKind [            // Node with children
        ChildNodeKind1 ( "token_text" )  // Leaf node with exact text
        ChildNodeKind2 [                  // Nested node with children
            ...
        ]
        Warn(WARNING_CODE)               // Warning node with an error code enum or const
        Error(ERROR_CODE)                // Error node with an error code enum or const
        ...                             // Ellipsis to skip remaining children in this subtree
    ]
);

• Root node: The first argument is the source code string to parse.
• Nodes with children: Use KindName [ ... ] where KindName is a variant of your SyntaxKind enum.
• Leaf tokens: Use KindName("token_text") where the string is the exact matched source token text.
• Warnings and errors: Use Warn(WARNING_CODE) and Error(ERROR_CODE) where the code is a known error/warning enum or constant.
• Ellipsis (...): Use to ignore remaining children in a node subtree (useful to reduce test verbosity).

Notes

• KindName must be a variant of your SyntaxKind enum (without the SyntaxKind:: prefix).
• Leaf nodes must specify the exact token text as a string literal.
• Warn and Error are reserved special nodes recognized by the macro for diagnostics.
• The macro performs strict ordering checks: children must appear in exact order as specified.

Example: Simple function call

compose_syntax::test_utils::assert_parse_tree!(
    "f(a, b: c)",
    FuncCall [
        Ident("f")
        Args [
            LeftParen("(")
            Ident("a")
            Comma(",")
            Named [ Ident("b") Colon(":") Ident("c") ]
            RightParen(")")
        ]
    ]
);

Example: Error recovery with warnings and errors

compose_syntax::test_utils::assert_parse_tree!(
    r#"
    f(a, b, c
    1 + 2
    "#,
    FuncCall [
        Ident("f")
        Args [
            Error(compose_error_codes::E0001_UNCLOSED_DELIMITER)
            Ident("a")
            Comma(",")
            Ident("b")
            Comma(",")
            Ident("c")
            Error(compose_error_codes::E0009_ARGS_MISSING_COMMAS)
            Binary [
                Int("1")
                Plus("+")
                Int("2")
            ]
        ]
    ]
);

Example: Skipping subtree content

compose_syntax::test_utils::assert_parse_tree!(
    "{ ref mut a => a }",
    Lambda [
        LeftBrace("{")
        Params [
            Param [
                Ref("ref")
                Mut("mut")
                Ident("a")
            ]
        ]
        ...
    ]
);

Common mistakes

• Forgetting to provide the exact token text string for leaf nodes results in a compile error.
• Using Warn or Error as SyntaxKind variants inside children nodes causes errors; they must use the special macro arms.

See also

• SyntaxKind enum variants — the node/kind names used in this macro.
• Parser error codes for Warn and Error nodes.
• NodesTester struct for underlying test traversal and assertions.