Recover more expressions in patterns

Author: ShE3py

compiler/rustc_parse/messages.ftl

@@ -774,15 +774,9 @@ 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

@@ -2422,8 +2422,6 @@ 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

@@ -41,14 +41,14 @@ use tracing::instrument;
 
 #[derive(Debug)]
 pub(super) enum LhsExpr {
-    // Already parsed just the outer attributes.
+    /// Already parsed just the outer attributes.
     Unparsed { attrs: AttrWrapper },
-    // Already parsed the expression.
+    /// Already parsed the expression.
     Parsed { expr: P<Expr>, starts_statement: bool },
 }
 
 #[derive(Debug)]
-enum DestructuredFloat {
+pub(super) enum DestructuredFloat {
     /// 1e2
     Single(Symbol, Span),
     /// 1.
@@ -1036,15 +1036,17 @@ impl<'a> Parser<'a> {
         self.dcx().emit_err(errors::UnexpectedTokenAfterDot { span, actual })
     }
 
-    // We need an identifier or integer, but the next token is a float.
-    // Break the float into components to extract the identifier or integer.
+    /// We need an identifier or integer, but the next token is a float.
+    /// Break the float into components to extract the identifier or integer.
+    ///
+    /// See also [`TokenKind::break_two_token_op`] which does similar splitting of `>>` into `>`.
+    //
     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
     // parts unless those parts are processed immediately. `TokenCursor` should either
     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
     // 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(super) 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, LhsExpr};
+use crate::parser::expr::{could_be_unclosed_char_literal, DestructuredFloat, LhsExpr};
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
 use rustc_ast::ptr::P;
@@ -337,46 +337,61 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Ensures that the last parsed pattern (or pattern range bound) is not followed by a method call or an operator.
+    /// Ensures that the last parsed pattern (or pattern range bound) is not followed by an expression.
     ///
     /// `is_end_bound` indicates whether the last parsed thing was the end bound of a range pattern (see [`parse_pat_range_end`](Self::parse_pat_range_end))
     /// in order to say "expected a pattern range bound" instead of "expected a pattern";
     /// ```text
     /// 0..=1 + 2
     ///     ^^^^^
     /// ```
-    /// Only the end bound is spanned, and this function have no idea if there were a `..=` before `pat_span`, hence the parameter.
+    /// Only the end bound is spanned in this case, 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_two_tuple_indexes = |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_two_tuple_indexes(&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;
         }
@@ -386,43 +401,40 @@ impl<'a> Parser<'a> {
         snapshot.restrictions.insert(Restrictions::IS_PAT);
 
         // Parse `?`, `.f`, `(arg0, arg1, ...)` or `[expr]` until they've all been eaten.
-        if let Ok(expr) = snapshot
+        let Ok(expr) = snapshot
             .parse_expr_dot_or_call_with(
                 self.mk_expr(pat_span, ExprKind::Dummy), // equivalent to transforming the parsed pattern into an `Expr`
                 pat_span,
                 AttrVec::new(),
             )
             .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`].
-            let lhs = LhsExpr::Parsed { expr, starts_statement: false };
-            if let Ok(expr) = snapshot.parse_expr_assoc_with(0, lhs).map_err(|err| err.cancel()) {
-                // We got a valid expression.
-                self.restore_snapshot(snapshot);
-                self.restrictions.remove(Restrictions::IS_PAT);
-
-                let is_bound = is_end_bound
-                    // is_start_bound: either `..` or `)..`
-                    || self.token.is_range_separator()
-                    || 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,
-                }));
-            }
-        }
+        else {
+            // We got a trailing method/operator, but that wasn't an expression.
+            return None;
+        };
+
+        // Parse an associative expression such as `+ expr`, `% expr`, ...
+        // Assignements, ranges and `|` are disabled by [`Restrictions::IS_PAT`].
+        let lhs = LhsExpr::Parsed { expr, starts_statement: false };
+        let Ok(expr) = snapshot.parse_expr_assoc_with(0, lhs).map_err(|err| err.cancel()) else {
+            // We got a trailing method/operator, but that wasn't an expression.
+            return None;
+        };
+
+        // We got a valid expression.
+        self.restore_snapshot(snapshot);
+        self.restrictions.remove(Restrictions::IS_PAT);
+
+        let is_bound = is_end_bound
+            // is_start_bound: either `..` or `)..`
+            || self.token.is_range_separator()
+            || self.token.kind == token::CloseDelim(Delimiter::Parenthesis)
+                && self.look_ahead(1, Token::is_range_separator);
 
-        // We got a trailing method/operator, but we couldn't parse an expression.
-        None
+        Some((
+            self.dcx().emit_err(UnexpectedExpressionInPattern { span: expr.span, is_bound }),
+            expr.span,
+        ))
     }
 
     /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
@@ -534,7 +546,7 @@ 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),
                 }
             }
@@ -567,10 +579,10 @@ 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)?,
@@ -700,7 +712,8 @@ 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;
 
@@ -718,7 +731,7 @@ 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)
@@ -733,15 +746,20 @@ 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 +1009,7 @@ 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 +1078,7 @@ 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.rs

@@ -1,5 +1,6 @@
-//@ error-pattern: expected
-
 fn main() {
   let x.y::<isize>.z foo;
+  //~^ error: field expressions cannot have generic arguments
+  //~| error: expected a pattern, found an expression
+  //~| error: expected one of `(`, `.`, `::`, `:`, `;`, `=`, `?`, `|`, or an operator, found `foo`
 }

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:2:12
    |
 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:2:7
+   |
+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:2:22
+   |
+LL |   let x.y::<isize>.z foo;
+   |                      ^^^ expected one of 9 possible tokens
+
+error: aborting due to 3 previous errors