Recover more expressions in patterns

Author: ShE3py

compiler/rustc_parse/messages.ftl

@@ -776,15 +776,9 @@ parse_unexpected_expr_in_pat =
     expected {$is_bound ->
         [true] a pattern range bound
        *[false] a pattern
-    }, found {$is_method_call ->
-        [true] a method call
-       *[false] an expression
-    }
+    }, found an expression
 
-    .label = {$is_method_call ->
-        [true] method calls
-       *[false] arbitrary expressions
-    } are not allowed in patterns
+    .label = arbitrary expressions are not allowed in patterns
 
 parse_unexpected_if_with_if = unexpected `if` in the condition expression
     .suggestion = remove the `if`

compiler/rustc_parse/src/errors.rs

@@ -2439,8 +2439,6 @@ pub(crate) struct UnexpectedExpressionInPattern {
     pub span: Span,
     /// Was a `RangePatternBound` expected?
     pub is_bound: bool,
-    /// Was the unexpected expression a `MethodCallExpression`?
-    pub is_method_call: bool,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_parse/src/parser/expr.rs

@@ -94,7 +94,7 @@ impl From<P<Expr>> for LhsExpr {
 }
 
 #[derive(Debug)]
-enum DestructuredFloat {
+pub(crate) enum DestructuredFloat {
     /// 1e2
     Single(Symbol, Span),
     /// 1.
@@ -1101,7 +1101,7 @@ impl<'a> Parser<'a> {
     // we should break everything including floats into more basic proc-macro style
     // tokens in the lexer (probably preferable).
     // See also `TokenKind::break_two_token_op` which does similar splitting of `>>` into `>`.
-    fn break_up_float(&self, float: Symbol, span: Span) -> DestructuredFloat {
+    pub(crate) fn break_up_float(&self, float: Symbol, span: Span) -> DestructuredFloat {
         #[derive(Debug)]
         enum FloatComponent {
             IdentLike(String),

compiler/rustc_parse/src/parser/pat.rs

@@ -10,7 +10,7 @@ use crate::errors::{
     UnexpectedParenInRangePatSugg, UnexpectedVertVertBeforeFunctionParam,
     UnexpectedVertVertInPattern,
 };
-use crate::parser::expr::could_be_unclosed_char_literal;
+use crate::parser::expr::{could_be_unclosed_char_literal, DestructuredFloat};
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
 use rustc_ast::ptr::P;
@@ -346,37 +346,51 @@ impl<'a> Parser<'a> {
     ///     ^^^^^
     /// ```
     /// Only the end bound is spanned, and this function have no idea if there were a `..=` before `pat_span`, hence the parameter.
+    /// This function returns `Some` if a trailing expression was recovered, and said expression's span.
     #[must_use = "the pattern must be discarded as `PatKind::Err` if this function returns Some"]
     fn maybe_recover_trailing_expr(
         &mut self,
         pat_span: Span,
         is_end_bound: bool,
-    ) -> Option<ErrorGuaranteed> {
+    ) -> Option<(ErrorGuaranteed, Span)> {
         if self.prev_token.is_keyword(kw::Underscore) || !self.may_recover() {
             // Don't recover anything after an `_` or if recovery is disabled.
             return None;
         }
 
-        // Check for `.hello()`, but allow `.Hello()` to be recovered as `, Hello()` in `parse_seq_to_before_tokens()`.
-        let has_trailing_method = self.check_noexpect(&token::Dot)
+        // Returns `true` iff `token` is a `x.y` float
+        let is_float_literal = |that: &Self, token: &Token| -> bool {
+            use token::{Lit, LitKind};
+
+            let token::Literal(Lit { kind: LitKind::Float, symbol, suffix: None }) = token.kind
+            else {
+                return false;
+            };
+
+            matches!(that.break_up_float(symbol, token.span), DestructuredFloat::MiddleDot(..))
+        };
+
+        // Check for `.hello` or `.0`.
+        let has_dot_expr = self.check_noexpect(&token::Dot) // `.`
             && self.look_ahead(1, |tok| {
-                tok.ident()
-                    .and_then(|(ident, _)| ident.name.as_str().chars().next())
-                    .is_some_and(char::is_lowercase)
-            })
-            && self.look_ahead(2, |tok| tok.kind == token::OpenDelim(Delimiter::Parenthesis));
+                tok.is_ident() // `hello`
+                || tok.is_integer_lit() // `0`
+                || is_float_literal(&self, &tok) // `0.0`
+            });
 
         // Check for operators.
         // `|` is excluded as it is used in pattern alternatives and lambdas,
         // `?` is included for error propagation,
         // `[` is included for indexing operations,
-        // `[]` is excluded as `a[]` isn't an expression and should be recovered as `a, []` (cf. `tests/ui/parser/pat-lt-bracket-7.rs`)
+        // `[]` is excluded as `a[]` isn't an expression and should be recovered as `a, []` (cf. `tests/ui/parser/pat-lt-bracket-7.rs`),
+        // `as` is included for type casts
         let has_trailing_operator = matches!(self.token.kind, token::BinOp(op) if op != BinOpToken::Or)
             || self.token.kind == token::Question
             || (self.token.kind == token::OpenDelim(Delimiter::Bracket)
-                && self.look_ahead(1, |tok| tok.kind != token::CloseDelim(Delimiter::Bracket)));
+                && self.look_ahead(1, |tok| tok.kind != token::CloseDelim(Delimiter::Bracket))) // excludes `[]`
+            || self.token.is_keyword(kw::As);
 
-        if !has_trailing_method && !has_trailing_operator {
+        if !has_dot_expr && !has_trailing_operator {
             // Nothing to recover here.
             return None;
         }
@@ -394,8 +408,6 @@ impl<'a> Parser<'a> {
             )
             .map_err(|err| err.cancel())
         {
-            let non_assoc_span = expr.span;
-
             // Parse an associative expression such as `+ expr`, `% expr`, ...
             // Assignements, ranges and `|` are disabled by [`Restrictions::IS_PAT`].
             if let Ok(expr) =
@@ -411,14 +423,11 @@ impl<'a> Parser<'a> {
                     || self.token.kind == token::CloseDelim(Delimiter::Parenthesis)
                         && self.look_ahead(1, Token::is_range_separator);
 
-                // Check that `parse_expr_assoc_with` didn't eat a rhs.
-                let is_method_call = has_trailing_method && non_assoc_span == expr.span;
-
-                return Some(self.dcx().emit_err(UnexpectedExpressionInPattern {
-                    span: expr.span,
-                    is_bound,
-                    is_method_call,
-                }));
+                return Some((
+                    self.dcx()
+                        .emit_err(UnexpectedExpressionInPattern { span: expr.span, is_bound }),
+                    expr.span,
+                ));
             }
         }
 
@@ -535,7 +544,7 @@ impl<'a> Parser<'a> {
                 self.parse_pat_tuple_struct(qself, path)?
             } else {
                 match self.maybe_recover_trailing_expr(span, false) {
-                    Some(guar) => PatKind::Err(guar),
+                    Some((guar, _)) => PatKind::Err(guar),
                     None => PatKind::Path(qself, path),
                 }
             }
@@ -568,10 +577,10 @@ impl<'a> Parser<'a> {
             // Try to parse everything else as literal with optional minus
             match self.parse_literal_maybe_minus() {
                 Ok(begin) => {
-                    let begin = match self.maybe_recover_trailing_expr(begin.span, false) {
-                        Some(guar) => self.mk_expr_err(begin.span, guar),
-                        None => begin,
-                    };
+                    let begin = self
+                        .maybe_recover_trailing_expr(begin.span, false)
+                        .map(|(guar, sp)| self.mk_expr_err(sp, guar))
+                        .unwrap_or(begin);
 
                     match self.parse_range_end() {
                         Some(form) => self.parse_pat_range_begin_with(begin, form)?,
@@ -701,7 +710,8 @@ impl<'a> Parser<'a> {
         // For backward compatibility, `(..)` is a tuple pattern as well.
         let paren_pattern =
             fields.len() == 1 && !(matches!(trailing_comma, Trailing::Yes) || fields[0].is_rest());
-        if paren_pattern {
+
+        let pat = if paren_pattern {
             let pat = fields.into_iter().next().unwrap();
             let close_paren = self.prev_token.span;
 
@@ -719,7 +729,7 @@ impl<'a> Parser<'a> {
                         },
                     });
 
-                    self.parse_pat_range_begin_with(begin.clone(), form)
+                    self.parse_pat_range_begin_with(begin.clone(), form)?
                 }
                 // recover ranges with parentheses around the `(start)..`
                 PatKind::Err(guar)
@@ -734,15 +744,20 @@ impl<'a> Parser<'a> {
                         },
                     });
 
-                    self.parse_pat_range_begin_with(self.mk_expr_err(pat.span, *guar), form)
+                    self.parse_pat_range_begin_with(self.mk_expr_err(pat.span, *guar), form)?
                 }
 
                 // (pat) with optional parentheses
-                _ => Ok(PatKind::Paren(pat)),
+                _ => PatKind::Paren(pat),
             }
         } else {
-            Ok(PatKind::Tuple(fields))
-        }
+            PatKind::Tuple(fields)
+        };
+
+        Ok(match self.maybe_recover_trailing_expr(open_paren.to(self.prev_token.span), false) {
+            None => pat,
+            Some((guar, _)) => PatKind::Err(guar),
+        })
     }
 
     /// Parse a mutable binding with the `mut` token already eaten.
@@ -991,7 +1006,7 @@ impl<'a> Parser<'a> {
         }
 
         Ok(match recovered {
-            Some(guar) => self.mk_expr_err(bound.span, guar),
+            Some((guar, sp)) => self.mk_expr_err(sp, guar),
             None => bound,
         })
     }
@@ -1060,7 +1075,7 @@ impl<'a> Parser<'a> {
         // but not `ident @ subpat` as `subpat` was already checked and `ident` continues with `@`.
 
         let pat = if sub.is_none()
-            && let Some(guar) = self.maybe_recover_trailing_expr(ident.span, false)
+            && let Some((guar, _)) = self.maybe_recover_trailing_expr(ident.span, false)
         {
             PatKind::Err(guar)
         } else {

tests/ui/parser/bad-name.stderr

@@ -1,8 +1,20 @@
-error: expected one of `:`, `;`, `=`, `@`, or `|`, found `.`
-  --> $DIR/bad-name.rs:4:8
+error: field expressions cannot have generic arguments
+  --> $DIR/bad-name.rs:4:12
    |
 LL |   let x.y::<isize>.z foo;
-   |        ^ expected one of `:`, `;`, `=`, `@`, or `|`
+   |            ^^^^^^^
 
-error: aborting due to 1 previous error
+error: expected a pattern, found an expression
+  --> $DIR/bad-name.rs:4:7
+   |
+LL |   let x.y::<isize>.z foo;
+   |       ^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
+
+error: expected one of `(`, `.`, `::`, `:`, `;`, `=`, `?`, `|`, or an operator, found `foo`
+  --> $DIR/bad-name.rs:4:22
+   |
+LL |   let x.y::<isize>.z foo;
+   |                      ^^^ expected one of 9 possible tokens
+
+error: aborting due to 3 previous errors
 

tests/ui/parser/pat-recover-exprs.rs

@@ -1,14 +1,14 @@
 fn main() {
     match u8::MAX {
         u8::MAX.abs() => (),
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         x.sqrt() @ .. => (),
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         //~| error: left-hand side of `@` must be a binding
         z @ w @ v.u() => (),
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         y.ilog(3) => (),
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         n + 1 => (),
         //~^ error: expected a pattern, found an expression
         ("".f() + 14 * 8) => (),

tests/ui/parser/pat-recover-exprs.stderr

@@ -1,14 +1,14 @@
-error: expected a pattern, found a method call
+error: expected a pattern, found an expression
   --> $DIR/pat-recover-exprs.rs:3:9
    |
 LL |         u8::MAX.abs() => (),
-   |         ^^^^^^^^^^^^^ method calls are not allowed in patterns
+   |         ^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
 
-error: expected a pattern, found a method call
+error: expected a pattern, found an expression
   --> $DIR/pat-recover-exprs.rs:5:9
    |
 LL |         x.sqrt() @ .. => (),
-   |         ^^^^^^^^ method calls are not allowed in patterns
+   |         ^^^^^^^^ arbitrary expressions are not allowed in patterns
 
 error: left-hand side of `@` must be a binding
   --> $DIR/pat-recover-exprs.rs:5:9
@@ -21,17 +21,17 @@ LL |         x.sqrt() @ .. => (),
    |
    = note: bindings are `x`, `mut x`, `ref x`, and `ref mut x`
 
-error: expected a pattern, found a method call
+error: expected a pattern, found an expression
   --> $DIR/pat-recover-exprs.rs:8:17
    |
 LL |         z @ w @ v.u() => (),
-   |                 ^^^^^ method calls are not allowed in patterns
+   |                 ^^^^^ arbitrary expressions are not allowed in patterns
 
-error: expected a pattern, found a method call
+error: expected a pattern, found an expression
   --> $DIR/pat-recover-exprs.rs:10:9
    |
 LL |         y.ilog(3) => (),
-   |         ^^^^^^^^^ method calls are not allowed in patterns
+   |         ^^^^^^^^^ arbitrary expressions are not allowed in patterns
 
 error: expected a pattern, found an expression
   --> $DIR/pat-recover-exprs.rs:12:9

tests/ui/parser/pat-recover-methodcalls.rs

@@ -4,15 +4,15 @@ struct Bar { baz: String }
 fn foo(foo: Foo) -> bool {
     match foo {
         Foo("hi".to_owned()) => true,
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         _ => false
     }
 }
 
 fn bar(bar: Bar) -> bool {
     match bar {
         Bar { baz: "hi".to_owned() } => true,
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         _ => false
     }
 }
@@ -22,16 +22,15 @@ fn baz() { // issue #90121
 
     match foo.as_slice() {
         &["foo".to_string()] => {}
-        //~^ error: expected a pattern, found a method call
+        //~^ error: expected a pattern, found an expression
         _ => {}
     };
 }
 
 fn main() {
     if let (-1.some(4)) = (0, Some(4)) {}
-    //~^ error: expected a pattern, found a method call
+    //~^ error: expected a pattern, found an expression
 
     if let (-1.Some(4)) = (0, Some(4)) {}
-    //~^ error: expected one of `)`, `,`, `...`, `..=`, `..`, or `|`, found `.`
-    //~| help: missing `,`
+    //~^ error: expected a pattern, found an expression
 }