diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs index 93400c67949d9..1e117c46b6e29 100644 --- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs +++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs @@ -780,7 +780,7 @@ impl<'a> State<'a> { } _ => { self.end(); // Close the ibox for the pattern. - self.print_expr(body, FixupContext::new_stmt()); + self.print_expr(body, FixupContext::new_match_arm()); self.word(","); } } diff --git a/compiler/rustc_ast_pretty/src/pprust/state/fixup.rs b/compiler/rustc_ast_pretty/src/pprust/state/fixup.rs index d21cb82f83b28..86d4796e9ce3b 100644 --- a/compiler/rustc_ast_pretty/src/pprust/state/fixup.rs +++ b/compiler/rustc_ast_pretty/src/pprust/state/fixup.rs @@ -49,6 +49,38 @@ pub(crate) struct FixupContext { /// No parentheses required. leftmost_subexpression_in_stmt: bool, + /// Print expression such that it can be parsed as a match arm. + /// + /// This is almost equivalent to `stmt`, but the grammar diverges a tiny bit + /// between statements and match arms when it comes to braced macro calls. + /// Macro calls with brace delimiter terminate a statement without a + /// semicolon, but do not terminate a match-arm without comma. + /// + /// ```ignore (illustrative) + /// m! {} - 1; // two statements: a macro call followed by -1 literal + /// + /// match () { + /// _ => m! {} - 1, // binary subtraction operator + /// } + /// ``` + match_arm: bool, + + /// This is almost equivalent to `leftmost_subexpression_in_stmt`, other + /// than for braced macro calls. + /// + /// If we have `m! {} - 1` as an expression, the leftmost subexpression + /// `m! {}` will need to be parenthesized in the statement case but not the + /// match-arm case. + /// + /// ```ignore (illustrative) + /// (m! {}) - 1; // subexpression needs parens + /// + /// match () { + /// _ => m! {} - 1, // no parens + /// } + /// ``` + leftmost_subexpression_in_match_arm: bool, + /// This is the difference between: /// /// ```ignore (illustrative) @@ -68,6 +100,8 @@ impl Default for FixupContext { FixupContext { stmt: false, leftmost_subexpression_in_stmt: false, + match_arm: false, + leftmost_subexpression_in_match_arm: false, parenthesize_exterior_struct_lit: false, } } @@ -76,13 +110,16 @@ impl Default for FixupContext { impl FixupContext { /// Create the initial fixup for printing an expression in statement /// position. - /// - /// This is currently also used for printing an expression as a match-arm, - /// but this is incorrect and leads to over-parenthesizing. pub fn new_stmt() -> Self { FixupContext { stmt: true, ..FixupContext::default() } } + /// Create the initial fixup for printing an expression as the right-hand + /// side of a match arm. + pub fn new_match_arm() -> Self { + FixupContext { match_arm: true, ..FixupContext::default() } + } + /// Create the initial fixup for printing an expression as the "condition" /// of an `if` or `while`. There are a few other positions which are /// grammatically equivalent and also use this, such as the iterator @@ -106,6 +143,9 @@ impl FixupContext { FixupContext { stmt: false, leftmost_subexpression_in_stmt: self.stmt || self.leftmost_subexpression_in_stmt, + match_arm: false, + leftmost_subexpression_in_match_arm: self.match_arm + || self.leftmost_subexpression_in_match_arm, ..self } } @@ -119,7 +159,13 @@ impl FixupContext { /// example the `$b` in `$a + $b` and `-$b`, but not the one in `[$b]` or /// `$a.f($b)`. pub fn subsequent_subexpression(self) -> Self { - FixupContext { stmt: false, leftmost_subexpression_in_stmt: false, ..self } + FixupContext { + stmt: false, + leftmost_subexpression_in_stmt: false, + match_arm: false, + leftmost_subexpression_in_match_arm: false, + ..self + } } /// Determine whether parentheses are needed around the given expression to @@ -128,7 +174,8 @@ impl FixupContext { /// The documentation on `FixupContext::leftmost_subexpression_in_stmt` has /// examples. pub fn would_cause_statement_boundary(self, expr: &Expr) -> bool { - self.leftmost_subexpression_in_stmt && !classify::expr_requires_semi_to_be_stmt(expr) + (self.leftmost_subexpression_in_stmt && !classify::expr_requires_semi_to_be_stmt(expr)) + || (self.leftmost_subexpression_in_match_arm && classify::expr_is_complete(expr)) } /// Determine whether parentheses are needed around the given `let` diff --git a/tests/ui/macros/stringify.rs b/tests/ui/macros/stringify.rs index a66a5513ffae3..472cb4d417be8 100644 --- a/tests/ui/macros/stringify.rs +++ b/tests/ui/macros/stringify.rs @@ -225,7 +225,7 @@ fn test_expr() { ); c2_match_arm!( [ m! {} - 1 ], - "match () { _ => (m! {}) - 1, }", // parenthesis is redundant + "match () { _ => m! {} - 1, }", "match () { _ => m! {} - 1 }", );