Replace `match_token` proc macro with `macro_rules!` macros #640

nicoburns · 2025-06-30T12:47:40Z

Experimental (feedback very welcome):

Allows the match_token! procedural macro to be replaced with a series of simpler macro_rules! macros combined with a regular match expression.

The following macro:

//§ the-before-html-insertion-mode
InsertionMode::BeforeHtml => match_token!(token {
    Token::Characters(SplitStatus::NotSplit, text) => ProcessResult::SplitWhitespace(text),
    Token::Characters(SplitStatus::Whitespace, _) => ProcessResult::Done,
    Token::Comment(text) => self.append_comment_to_doc(text),

    tag @ <html> => {
        self.create_root(tag.attrs);
        self.mode.set(InsertionMode::BeforeHead);
        ProcessResult::Done
    }

    </head> </body> </html> </br> => else,

    tag @ </_> => self.unexpected(&tag),

    token => {
        self.create_root(vec!());
        ProcessResult::Reprocess(InsertionMode::BeforeHead, token)
    }
}),

would be replaced with:

//§ the-before-html-insertion-mode
InsertionMode::BeforeHtml => match token {
    Token::Characters(SplitStatus::NotSplit, text) => {
        ProcessResult::SplitWhitespace(text)
    },
    Token::Characters(SplitStatus::Whitespace, _) => ProcessResult::Done,
    Token::Comment(text) => self.append_comment_to_doc(text),

    // Token::Tag(tag @ tag!(["html"] | [/"body"])) => {
    tag_token!(tag @ ["html"] | [/"body"]) => {
        self.create_root(tag.attrs);
        self.mode.set(InsertionMode::BeforeHead);
        ProcessResult::Done
    },

    // Token::Tag(tag @ any_end_tag!()) if !matches!(tag, tag!([/"head"] | [/"body"] | [/"html"] | [/"br"])) =>
    any_end_tag_token!(tag) if is_not_tag!(tag, [/"head"] | [/"body"] | [/"html"] | [/"br"]) => {
        self.unexpected(&tag)
    },

    token => {
        self.create_root(vec!());
        ProcessResult::Reprocess(InsertionMode::BeforeHead, token)
    },
},

(commented out lines are an alternative variant that is also possible (would replace the line immediately below themselves))

Signed-off-by: Nico Burns <[email protected]>

simonwuelker

I like the idea!

Having to write tag_token!(tag @ ["html"] | [/"body"]) is odd though.
Can't it be tag_token!(tag @ <html> | </body>) if the macro match arm is changed from (__inner:[/$tag:tt]) to something like (__inner:</$tag:ident>)?

You could convert the ident to a tt using the stringify macro and that would remove the need for quotes at the macro invocation site.

nicoburns requested review from mrobinson and simonwuelker June 30, 2025 12:47

nicoburns force-pushed the declarative_match_token branch from 62ef04d to 762a26e Compare June 30, 2025 12:49

Replace match_token with macro_rules macros

1ead52f

Signed-off-by: Nico Burns <[email protected]>

nicoburns force-pushed the declarative_match_token branch from 762a26e to 1ead52f Compare June 30, 2025 12:50

simonwuelker reviewed Jul 3, 2025

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Replace `match_token` proc macro with `macro_rules!` macros #640

Replace `match_token` proc macro with `macro_rules!` macros #640

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nicoburns commented Jun 30, 2025 •

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Replace match_token proc macro with macro_rules! macros #640

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Replace `match_token` proc macro with `macro_rules!` macros #640

Replace `match_token` proc macro with `macro_rules!` macros #640

nicoburns commented Jun 30, 2025 •

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