Special case matches! macro

src/expr.rs

@@ -1446,7 +1446,10 @@ fn rewrite_float_lit(
     .max_width_error(shape.width, span)
 }
 
-fn choose_separator_tactic(context: &RewriteContext<'_>, span: Span) -> Option<SeparatorTactic> {
+pub(crate) fn choose_separator_tactic(
+    context: &RewriteContext<'_>,
+    span: Span,
+) -> Option<SeparatorTactic> {
     if context.inside_macro() {
         if span_ends_with_comma(context, span) {
             Some(SeparatorTactic::Always)

src/macros.rs

@@ -24,10 +24,12 @@ use crate::comment::{
 };
 use crate::config::StyleEdition;
 use crate::config::lists::*;
-use crate::expr::{RhsAssignKind, rewrite_array, rewrite_assign_rhs};
+use crate::expr::{RhsAssignKind, choose_separator_tactic, rewrite_array, rewrite_assign_rhs};
 use crate::lists::{ListFormatting, itemize_list, write_list};
+use crate::matches::rewrite_guard;
 use crate::overflow;
 use crate::parse::macros::lazy_static::parse_lazy_static;
+use crate::parse::macros::matches::{MatchesMacroItem, parse_matches};
 use crate::parse::macros::{ParsedMacroArgs, parse_expr, parse_macro_args};
 use crate::rewrite::{
     MacroErrorKind, Rewrite, RewriteContext, RewriteError, RewriteErrorExt, RewriteResult,
@@ -238,6 +240,12 @@ fn rewrite_macro_inner(
                 _ => return Err(err),
             },
         }
+    } else if macro_name == "matches!"
+        && context.config.style_edition() >= StyleEdition::Edition2027
+    {
+        if let success @ Ok(..) = format_matches(context, shape, &macro_name, mac) {
+            return success;
+        }
     }
 
     let ParsedMacroArgs {
@@ -1394,6 +1402,67 @@ impl MacroBranch {
     }
 }
 
+impl Rewrite for MatchesMacroItem {
+    fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
+        self.rewrite_result(context, shape).ok()
+    }
+
+    fn rewrite_result(
+        &self,
+        context: &RewriteContext<'_>,
+        shape: crate::shape::Shape,
+    ) -> RewriteResult {
+        match self {
+            Self::Expr(expr) => expr.rewrite_result(context, shape),
+            Self::Arm(pat, guard) => {
+                let pats_str = pat.rewrite_result(context, shape)?;
+                let guard_str = rewrite_guard(context, guard, shape, &pats_str)?;
+                Ok(pats_str + &guard_str)
+            }
+        }
+    }
+}
+
+/// Format `matches!` from <https://doc.rust-lang.org/std/macro.matches.html>
+///
+/// # Expected syntax
+///
+/// ```text
+/// matches!(expr, pat)
+/// matches!(expr, pat if expr)
+/// ```
+fn format_matches(
+    context: &RewriteContext<'_>,
+    shape: Shape,
+    name: &str,
+    mac: &ast::MacCall,
+) -> RewriteResult {
+    let span = mac.span();
+    let matches = parse_matches(context, mac.args.tokens.clone())?.items();
+    let force_separator_tactic = choose_separator_tactic(context, span);
+    match mac.args.delim {
+        Delimiter::Parenthesis => overflow::rewrite_with_parens(
+            context,
+            name,
+            matches.iter(),
+            shape,
+            span,
+            shape.width,
+            force_separator_tactic,
+        ),
+        Delimiter::Bracket => overflow::rewrite_with_square_brackets(
+            context,
+            name,
+            matches.iter(),
+            shape,
+            span,
+            force_separator_tactic,
+            None,
+        ),
+        Delimiter::Brace | Delimiter::Invisible(_) => Err(RewriteError::Unknown),
+    }
+}
+
 /// Format `lazy_static!` from <https://crates.io/crates/lazy_static>.
 ///
 /// # Expected syntax

src/matches.rs

@@ -296,15 +296,7 @@ fn rewrite_match_arm(
     let pats_str = arm.pat.rewrite_result(context, pat_shape)?;
 
     // Guard
-    let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
-    let new_line_guard = pats_str.contains('\n') && !block_like_pat;
-    let guard_str = rewrite_guard(
-        context,
-        &arm.guard,
-        shape,
-        trimmed_last_line_width(&pats_str),
-        new_line_guard,
-    )?;
+    let guard_str = rewrite_guard(context, &arm.guard, shape, &pats_str)?;
 
     let lhs_str = combine_strs_with_missing_comments(
         context,
@@ -568,8 +560,26 @@ fn rewrite_match_body(
     }
 }
 
+pub(crate) fn rewrite_guard(
+    context: &RewriteContext<'_>,
+    guard: &Option<ptr::P<ast::Expr>>,
+    shape: Shape,
+    pattern_str: &str,
+) -> RewriteResult {
+    let last_line_pattern_width = trimmed_last_line_width(pattern_str);
+    let block_like_pat = last_line_pattern_width <= context.config.tab_spaces();
+    let new_line_guard = pattern_str.contains('\n') && !block_like_pat;
+    rewrite_guard_inner(
+        context,
+        guard,
+        shape,
+        last_line_pattern_width,
+        new_line_guard,
+    )
+}
+
 // The `if ...` guard on a match arm.
-fn rewrite_guard(
+fn rewrite_guard_inner(
     context: &RewriteContext<'_>,
     guard: &Option<ptr::P<ast::Expr>>,
     shape: Shape,

src/overflow.rs

@@ -19,6 +19,7 @@ use crate::lists::{
     ListFormatting, ListItem, Separator, definitive_tactic, itemize_list, write_list,
 };
 use crate::macros::MacroArg;
+use crate::parse::macros::matches::MatchesMacroItem;
 use crate::patterns::{TuplePatField, can_be_overflowed_pat};
 use crate::rewrite::{Rewrite, RewriteContext, RewriteError, RewriteErrorExt, RewriteResult};
 use crate::shape::Shape;
@@ -85,6 +86,7 @@ pub(crate) enum OverflowableItem<'a> {
     Ty(&'a ast::Ty),
     Pat(&'a ast::Pat),
     PreciseCapturingArg(&'a ast::PreciseCapturingArg),
+    MatchesMacroItem(&'a MatchesMacroItem),
 }
 
 impl<'a> Rewrite for OverflowableItem<'a> {
@@ -130,6 +132,7 @@ impl<'a> OverflowableItem<'a> {
             OverflowableItem::Ty(ty) => f(*ty),
             OverflowableItem::Pat(pat) => f(*pat),
             OverflowableItem::PreciseCapturingArg(arg) => f(*arg),
+            OverflowableItem::MatchesMacroItem(item) => f(*item),
         }
     }
 
@@ -154,7 +157,9 @@ impl<'a> OverflowableItem<'a> {
     pub(crate) fn is_expr(&self) -> bool {
         matches!(
             self,
-            OverflowableItem::Expr(..) | OverflowableItem::MacroArg(MacroArg::Expr(..))
+            OverflowableItem::Expr(..)
+                | OverflowableItem::MacroArg(MacroArg::Expr(..))
+                | OverflowableItem::MatchesMacroItem(MatchesMacroItem::Expr(..))
         )
     }
 
@@ -170,6 +175,7 @@ impl<'a> OverflowableItem<'a> {
         match self {
             OverflowableItem::Expr(expr) => Some(expr),
             OverflowableItem::MacroArg(MacroArg::Expr(ref expr)) => Some(expr),
+            OverflowableItem::MatchesMacroItem(MatchesMacroItem::Expr(expr)) => Some(expr),
             _ => None,
         }
     }
@@ -265,7 +271,10 @@ impl_into_overflowable_item_for_ast_node!(
     Pat,
     PreciseCapturingArg
 );
-impl_into_overflowable_item_for_rustfmt_types!([MacroArg], [SegmentParam, TuplePatField]);
+impl_into_overflowable_item_for_rustfmt_types!(
+    [MacroArg, MatchesMacroItem],
+    [SegmentParam, TuplePatField]
+);
 
 pub(crate) fn into_overflowable_list<'a, T>(
     iter: impl Iterator<Item = &'a T>,

src/parse/macros/matches.rs

@@ -0,0 +1,71 @@
+use rustc_ast::ast;
+use rustc_ast::ptr::P;
+use rustc_ast::tokenstream::TokenStream;
+use rustc_parse::exp;
+use rustc_parse::parser::{CommaRecoveryMode, RecoverColon, RecoverComma};
+
+use super::is_token_tree_comma;
+use crate::rewrite::{RewriteContext, RewriteError};
+
+#[derive(Debug)]
+pub(crate) struct Matches {
+    pub(crate) expr: P<ast::Expr>,
+    pub(crate) pat: P<ast::Pat>,
+    pub(crate) guard: Option<P<ast::Expr>>,
+}
+
+/// Parse matches! from <https://doc.rust-lang.org/std/macro.matches.html>
+pub(crate) fn parse_matches(
+    context: &RewriteContext<'_>,
+    ts: TokenStream,
+) -> Result<Matches, RewriteError> {
+    let mut cursor = ts.iter().peekable();
+    // remove trailing commmas from the TokenStream since they lead to errors when parsing ast::Pat
+    // using parse_pat_allow_top_alt below since the parser isn't expecting a trailing comma.
+    // This is only an issue when the `ast::Pat` is not followed by a guard. In either case it's ok
+    // to remove the comma from the stream since we don't need it to parse into a Matches struct
+    let mut token_trees = vec![];
+    while let Some(tt) = cursor.next() {
+        let is_last = cursor.peek().is_none();
+        if !(is_last && is_token_tree_comma(tt)) {
+            token_trees.push(tt.clone())
+        }
+    }
+
+    let ts = token_trees.into_iter().collect();
+    let mut parser = super::build_parser(context, ts);
+    let expr = parser.parse_expr().map_err(|_| RewriteError::Unknown)?;
+
+    let _ = parser.eat(exp!(Comma));
+
+    let pat = parser
+        .parse_pat_allow_top_guard(
+            None,
+            RecoverComma::Yes,
+            RecoverColon::Yes,
+            CommaRecoveryMode::EitherTupleOrPipe,
+        )
+        .map_err(|_| RewriteError::Unknown)?;
+
+    let guard = if parser.eat_keyword(exp!(If)) {
+        Some(parser.parse_expr().map_err(|_| RewriteError::Unknown)?)
+    } else {
+        None
+    };
+    Ok(Matches { expr, pat, guard })
+}
+
+impl Matches {
+    pub(crate) fn items(self) -> [MatchesMacroItem; 2] {
+        [
+            MatchesMacroItem::Expr(self.expr),
+            MatchesMacroItem::Arm(self.pat, self.guard),
+        ]
+    }
+}
+
+#[derive(Debug)]
+pub(crate) enum MatchesMacroItem {
+    Expr(P<ast::Expr>),
+    Arm(P<ast::Pat>, Option<P<ast::Expr>>),
+}

src/parse/macros/mod.rs

@@ -1,5 +1,5 @@
 use rustc_ast::token::{Delimiter, NonterminalKind, NtExprKind::*, NtPatKind::*, TokenKind};
-use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::{ast, ptr};
 use rustc_parse::MACRO_ARGUMENTS;
 use rustc_parse::parser::{ForceCollect, Parser, Recovery};
@@ -13,6 +13,7 @@ pub(crate) mod asm;
 pub(crate) mod cfg_if;
 pub(crate) mod cfg_match;
 pub(crate) mod lazy_static;
+pub(crate) mod matches;
 
 fn build_stream_parser<'a>(psess: &'a ParseSess, tokens: TokenStream) -> Parser<'a> {
     Parser::new(psess, tokens, MACRO_ARGUMENTS).recovery(Recovery::Forbidden)
@@ -96,6 +97,11 @@ fn check_keyword<'a, 'b: 'a>(parser: &'a mut Parser<'b>) -> Option<MacroArg> {
     }
 }
 
+/// Helper function to determine if a tokentree is a comma
+pub(crate) fn is_token_tree_comma(tt: &TokenTree) -> bool {
+    matches!(tt, TokenTree::Token(token, _) if token.kind == TokenKind::Comma)
+}
+
 pub(crate) fn parse_macro_args(
     context: &RewriteContext<'_>,
     tokens: TokenStream,

src/spanned.rs

@@ -4,6 +4,7 @@ use rustc_ast::{ast, ptr};
 use rustc_span::{Span, source_map};
 
 use crate::macros::MacroArg;
+use crate::parse::macros::matches::MatchesMacroItem;
 use crate::patterns::RangeOperand;
 use crate::utils::{mk_sp, outer_attributes};
 
@@ -211,3 +212,13 @@ impl<'a, T> Spanned for RangeOperand<'a, T> {
         self.span
     }
 }
+
+impl Spanned for MatchesMacroItem {
+    fn span(&self) -> rustc_span::Span {
+        match self {
+            Self::Expr(expr) => expr.span,
+            Self::Arm(pat, None) => pat.span,
+            Self::Arm(pat, Some(guard)) => mk_sp(pat.span.lo(), guard.span.hi()),
+        }
+    }
+}

tests/source/issue_5709.rs

@@ -0,0 +1,9 @@
+// rustfmt-style_edition: 2027
+
+fn is_something(foo: Foo, bar: Bar) -> bool {
+    matches!((legacy_required_finality, signature_weight),
+        | (LegacyRequiredFinality::Any, Insufficient | Weak | Strict)
+        | (LegacyRequiredFinality::Weak, Weak | Strict)
+        | (LegacyRequiredFinality::Strict, Strict)
+    )
+}

tests/source/issue_6650.rs

@@ -0,0 +1,5 @@
+// rustfmt-style_edition: 2027
+
+fn main() {
+    matches!(stmt, ast::Stmt{kind: ast::StmtKind::MacCall(box ast::MacCallStmt {style : ast::MacStmtStyle::Braces,..}),..})
+}