clippy_lints/src/nonstandard_macro_braces.rs

use clippy_config::Conf;
use clippy_config::types::MacroMatcher;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::{SourceText, SpanExt};
use rustc_ast::ast;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::Applicability;
use rustc_hir::def_id::DefId;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::impl_lint_pass;
use rustc_span::Span;
use rustc_span::hygiene::{ExpnKind, MacroKind};

declare_clippy_lint! {
    /// ### What it does
    /// Checks that common macros are used with consistent bracing.
    ///
    /// ### Why is this bad?
    /// Having non-conventional braces on well-stablished macros can be confusing
    /// when debugging, and they bring incosistencies with the rest of the ecosystem.
    ///
    /// ### Example
    /// ```no_run
    /// vec!{1, 2, 3};
    /// ```
    /// Use instead:
    /// ```no_run
    /// vec![1, 2, 3];
    /// ```
    #[clippy::version = "1.55.0"]
    pub NONSTANDARD_MACRO_BRACES,
    nursery,
    "check consistent use of braces in macro"
}

impl_lint_pass!(MacroBraces => [NONSTANDARD_MACRO_BRACES]);

struct MacroInfo {
    callsite_span: Span,
    callsite_snippet: SourceText,
    old_open_brace: char,
    braces: (char, char),
}

pub struct MacroBraces {
    macro_braces: FxHashMap<String, (char, char)>,
    done: FxHashSet<Span>,
}

impl MacroBraces {
    pub fn new(conf: &'static Conf) -> Self {
        Self {
            macro_braces: macro_braces(&conf.standard_macro_braces),
            done: FxHashSet::default(),
        }
    }
}

impl EarlyLintPass for MacroBraces {
    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
        if let Some(MacroInfo {
            callsite_span,
            callsite_snippet,
            braces,
            ..
        }) = is_offending_macro(cx, item.span, self)
        {
            emit_help(cx, &callsite_snippet, braces, callsite_span, false);
            self.done.insert(callsite_span);
        }
    }

    fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
        if let Some(MacroInfo {
            callsite_span,
            callsite_snippet,
            braces,
            old_open_brace,
        }) = is_offending_macro(cx, stmt.span, self)
        {
            // if we turn `macro!{}` into `macro!()`/`macro![]`, we'll no longer get the implicit
            // trailing semicolon, see #9913
            // NOTE: `stmt.kind != StmtKind::MacCall` because `EarlyLintPass` happens after macro expansion
            let add_semi = matches!(stmt.kind, ast::StmtKind::Expr(..)) && old_open_brace == '{';
            emit_help(cx, &callsite_snippet, braces, callsite_span, add_semi);
            self.done.insert(callsite_span);
        }
    }

    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
        if let Some(MacroInfo {
            callsite_span,
            callsite_snippet,
            braces,
            ..
        }) = is_offending_macro(cx, expr.span, self)
        {
            emit_help(cx, &callsite_snippet, braces, callsite_span, false);
            self.done.insert(callsite_span);
        }
    }

    fn check_ty(&mut self, cx: &EarlyContext<'_>, ty: &ast::Ty) {
        if let Some(MacroInfo {
            callsite_span,
            braces,
            callsite_snippet,
            ..
        }) = is_offending_macro(cx, ty.span, self)
        {
            emit_help(cx, &callsite_snippet, braces, callsite_span, false);
            self.done.insert(callsite_span);
        }
    }
}

fn is_offending_macro(cx: &EarlyContext<'_>, span: Span, mac_braces: &MacroBraces) -> Option<MacroInfo> {
    let unnested_or_local = |span: Span| {
        !span.from_expansion()
            || span
                .macro_backtrace()
                .last()
                .is_some_and(|e| e.macro_def_id.is_some_and(DefId::is_local))
    };

    let mut ctxt = span.ctxt();
    while !ctxt.is_root() {
        let expn_data = ctxt.outer_expn_data();
        if let ExpnKind::Macro(MacroKind::Bang, mac_name) = expn_data.kind
        && let name = mac_name.as_str()
        && let Some(&braces) = mac_braces.macro_braces.get(name)
        && let Some(snip) = expn_data.call_site.get_text(cx)
        // we must check only invocation sites
        // https://github.com/rust-lang/rust-clippy/issues/7422
        && let Some(macro_args_str) = snip.strip_prefix(name).and_then(|snip| snip.strip_prefix('!'))
        && let Some(old_open_brace @ ('{' | '(' | '[')) = macro_args_str.trim_start().chars().next()
        && old_open_brace != braces.0
        && unnested_or_local(expn_data.call_site)
        && !mac_braces.done.contains(&expn_data.call_site)
        {
            return Some(MacroInfo {
                callsite_span: expn_data.call_site,
                callsite_snippet: snip,
                old_open_brace,
                braces,
            });
        }

        ctxt = expn_data.call_site.ctxt();
    }

    None
}

fn emit_help(cx: &EarlyContext<'_>, snip: &str, (open, close): (char, char), span: Span, add_semi: bool) {
    let semi = if add_semi { ";" } else { "" };
    if let Some((macro_name, macro_args_str)) = snip.split_once('!') {
        let mut macro_args = macro_args_str.trim().to_string();
        // now remove the wrong braces
        macro_args.pop();
        macro_args.remove(0);
        span_lint_and_sugg(
            cx,
            NONSTANDARD_MACRO_BRACES,
            span,
            format!("use of irregular braces for `{macro_name}!` macro"),
            "consider writing",
            format!("{macro_name}!{open}{macro_args}{close}{semi}"),
            Applicability::MachineApplicable,
        );
    }
}

fn macro_braces(conf: &[MacroMatcher]) -> FxHashMap<String, (char, char)> {
    let mut braces = FxHashMap::from_iter(
        [
            ("print", ('(', ')')),
            ("println", ('(', ')')),
            ("eprint", ('(', ')')),
            ("eprintln", ('(', ')')),
            ("write", ('(', ')')),
            ("writeln", ('(', ')')),
            ("format", ('(', ')')),
            ("format_args", ('(', ')')),
            ("vec", ('[', ']')),
            ("matches", ('(', ')')),
        ]
        .map(|(k, v)| (k.to_string(), v)),
    );
    // We want users items to override any existing items
    for it in conf {
        braces.insert(it.name.clone(), it.braces);
    }
    braces
}