Support conditions

[stevefan1999-personal]

Right now I have to write this:

#[cfg(feature = "transpile")]
pub fn infer_transpile_syntax_by_extension(extension: &str) -> eyre::Result<Syntax> {
    trie_match::trie_match! {
        match extension {
            "js" | "mjs" => { Some(Syntax::Es(Default::default())) }
            "jsx" | "mjsx" => {
                if cfg!(feature = "react") {
                    Some(Syntax::Es(EsConfig { jsx: true, ..Default::default() }))
                } else {
                    None
                }
            }
            "ts" => {
                if cfg!(feature = "typescript") {
                    Some(Syntax::Typescript(Default::default()))
                } else {
                    None
                }
            }
            "tsx" => {
                if cfg!(all(feature = "typescript", feature = "react")) {
                    Some(Syntax::Typescript(TsConfig { tsx: true, ..Default::default() }))
                } else {
                    None
                }
            }
            _ => { None }
        }
    }
    .ok_or(eyre!("invalid extension"))
}

Rather than this:

pub fn infer_transpile_syntax_by_extension(extension: &str) -> eyre::Result<Syntax> {
    match extension {
        "js" | "mjs" => { Ok(Syntax::Es(Default::default())) }
        ("jsx" | "mjsx") if cfg!(feature = "react") => {
            Ok(Syntax::Es(EsConfig { jsx: true, ..Default::default() }))
        }
        "ts" if cfg!(feature = "typescript") => {
            Ok(Syntax::Typescript(Default::default()))
        }
        "tsx" if cfg!(all(feature = "typescript", feature = "react")) => {
            Ok(Syntax::Typescript(TsConfig { tsx: true, ..Default::default() }))
        }
        _ => { Err(eyre!("invalid extension")) }
    }
}

And neither this:

pub fn infer_transpile_syntax_by_extension(extension: &str) -> eyre::Result<Syntax> {
    match extension {
        "js" | "mjs" => Ok(Syntax::Es(Default::default())),
        #[cfg(feature = "react")]
        "jsx" | "mjsx" => {
            Ok(Syntax::Es(EsConfig {
                jsx: true,
                ..Default::default()
            }))
        }
        #[cfg(feature = "typescript")]
        "ts" => Ok(Syntax::Typescript(Default::default())),
        #[cfg(all(feature = "typescript", feature = "react"))]
        "tsx" => {
            Ok(Syntax::Typescript(TsConfig {
                tsx: true,
                ..Default::default()
            }))
        }
        _ => Err(eyre!("invalid extension")),
    }
}

[vbkaisetsu]

@stevefan1999-personal Thank you for your suggestion.
I created a pull request #10 to support #[cfg(...)] attribute, but this feature is only available with Nightly Rust.

If there are no problems, I will ask another member of the team to review the code.