Simplify pattern grammar by allowing nested leading vert

Along the way, we also implement a handful of diagnostics improvements
and fixes, particularly with respect to the special handling of `||` in
place of `|` and when there are leading verts in function params, which
don't allow top-level or-patterns anyway.

compiler/rustc_expand/src/expand.rs

@@ -22,7 +22,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, PResult};
 use rustc_feature::Features;
-use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, Parser};
+use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, GateOr, Parser, RecoverComma};
 use rustc_parse::validate_attr;
 use rustc_session::lint::builtin::UNUSED_DOC_COMMENTS;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -914,7 +914,9 @@ pub fn parse_ast_fragment<'a>(
             }
         }
         AstFragmentKind::Ty => AstFragment::Ty(this.parse_ty()?),
-        AstFragmentKind::Pat => AstFragment::Pat(this.parse_pat(None)?),
+        AstFragmentKind::Pat => {
+            AstFragment::Pat(this.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)?)
+        }
         AstFragmentKind::Arms
         | AstFragmentKind::Fields
         | AstFragmentKind::FieldPats

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1654,7 +1654,7 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
-        let pat = self.parse_pat(Some("argument name"))?;
+        let pat = self.parse_pat_no_top_alt(Some("argument name"))?;
         self.expect(&token::Colon)?;
         let ty = self.parse_ty()?;
 

compiler/rustc_parse/src/parser/expr.rs

@@ -1726,7 +1726,7 @@ impl<'a> Parser<'a> {
         let lo = self.token.span;
         let attrs = self.parse_outer_attributes()?;
         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
-            let pat = this.parse_pat(PARAM_EXPECTED)?;
+            let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
             let ty = if this.eat(&token::Colon) {
                 this.parse_ty()?
             } else {
@@ -1803,7 +1803,7 @@ impl<'a> Parser<'a> {
     /// The `let` token has already been eaten.
     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
         let lo = self.prev_token.span;
-        let pat = self.parse_top_pat(GateOr::No, RecoverComma::Yes)?;
+        let pat = self.parse_pat_allow_top_alt(None, GateOr::No, RecoverComma::Yes)?;
         self.expect(&token::Eq)?;
         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
@@ -1866,7 +1866,7 @@ impl<'a> Parser<'a> {
             _ => None,
         };
 
-        let pat = self.parse_top_pat(GateOr::Yes, RecoverComma::Yes)?;
+        let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::Yes)?;
         if !self.eat_keyword(kw::In) {
             self.error_missing_in_for_loop();
         }
@@ -1977,7 +1977,7 @@ impl<'a> Parser<'a> {
         let attrs = self.parse_outer_attributes()?;
         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
             let lo = this.token.span;
-            let pat = this.parse_top_pat(GateOr::No, RecoverComma::Yes)?;
+            let pat = this.parse_pat_allow_top_alt(None, GateOr::No, RecoverComma::Yes)?;
             let guard = if this.eat_keyword(kw::If) {
                 let if_span = this.prev_token.span;
                 let cond = this.parse_expr()?;

compiler/rustc_parse/src/parser/mod.rs

@@ -14,6 +14,7 @@ use crate::lexer::UnmatchedBrace;
 pub use attr_wrapper::AttrWrapper;
 pub use diagnostics::AttemptLocalParseRecovery;
 use diagnostics::Error;
+pub use pat::{GateOr, RecoverComma};
 pub use path::PathStyle;
 
 use rustc_ast::ptr::P;

compiler/rustc_parse/src/parser/nonterminal.rs

@@ -120,9 +120,9 @@ impl<'a> Parser<'a> {
             },
             NonterminalKind::Pat2018 { .. } | NonterminalKind::Pat2021 { .. } => {
                 token::NtPat(self.collect_tokens_no_attrs(|this| match kind {
-                    NonterminalKind::Pat2018 { .. } => this.parse_pat(None),
+                    NonterminalKind::Pat2018 { .. } => this.parse_pat_no_top_alt(None),
                     NonterminalKind::Pat2021 { .. } => {
-                        this.parse_top_pat(GateOr::Yes, RecoverComma::No)
+                        this.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
                     }
                     _ => unreachable!(),
                 })?)

compiler/rustc_parse/src/parser/pat.rs

@@ -19,14 +19,14 @@ const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here"
 
 /// Whether or not an or-pattern should be gated when occurring in the current context.
 #[derive(PartialEq, Clone, Copy)]
-pub(super) enum GateOr {
+pub enum GateOr {
     Yes,
     No,
 }
 
 /// Whether or not to recover a `,` when parsing or-patterns.
 #[derive(PartialEq, Copy, Clone)]
-pub(super) enum RecoverComma {
+pub enum RecoverComma {
     Yes,
     No,
 }
@@ -37,80 +37,57 @@ impl<'a> Parser<'a> {
     /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
     /// at the top level. Used when parsing the parameters of lambda expressions,
     /// functions, function pointers, and `pat` macro fragments.
-    pub fn parse_pat(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
+    pub fn parse_pat_no_top_alt(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
         self.parse_pat_with_range_pat(true, expected)
     }
 
-    /// Entry point to the main pattern parser.
+    /// Parses a pattern.
+    ///
     /// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
-    pub(super) fn parse_top_pat(
+    /// Used for parsing patterns in all cases when `pat<no_top_alt>` is not used.
-        &mut self,
+    ///
-        gate_or: GateOr,
+    /// Note that after the FCP in <https://github.com/rust-lang/rust/issues/81415>,
-        rc: RecoverComma,
+    /// a leading vert is allowed in nested or-patterns, too. This allows us to
-    ) -> PResult<'a, P<Pat>> {
+    /// simplify the grammar somewhat.
-        // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
+    pub fn parse_pat_allow_top_alt(
-        let gated_leading_vert = self.eat_or_separator(None) && gate_or == GateOr::Yes;
-        let leading_vert_span = self.prev_token.span;
-
-        // Parse the possibly-or-pattern.
-        let pat = self.parse_pat_with_or(None, gate_or, rc)?;
-
-        // If we parsed a leading `|` which should be gated,
-        // and no other gated or-pattern has been parsed thus far,
-        // then we should really gate the leading `|`.
-        // This complicated procedure is done purely for diagnostics UX.
-        if gated_leading_vert && self.sess.gated_spans.is_ungated(sym::or_patterns) {
-            self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
-        }
-
-        Ok(pat)
-    }
-
-    /// Parse the pattern for a function or function pointer parameter.
-    /// Special recovery is provided for or-patterns and leading `|`.
-    pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
-        self.recover_leading_vert(None, "not allowed in a parameter pattern");
-        let pat = self.parse_pat_with_or(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
-
-        if let PatKind::Or(..) = &pat.kind {
-            self.ban_illegal_fn_param_or_pat(&pat);
-        }
-
-        Ok(pat)
-    }
-
-    /// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
-    fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
-        let msg = "wrap the pattern in parenthesis";
-        let fix = format!("({})", pprust::pat_to_string(pat));
-        self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parenthesis")
-            .span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
-            .emit();
-    }
-
-    /// Parses a pattern, that may be a or-pattern (e.g. `Foo | Bar` in `Some(Foo | Bar)`).
-    /// Corresponds to `pat<allow_top_alt>` in RFC 2535.
-    fn parse_pat_with_or(
         &mut self,
         expected: Expected,
         gate_or: GateOr,
         rc: RecoverComma,
     ) -> PResult<'a, P<Pat>> {
+        // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
+        let leading_vert_span =
+            if self.eat_or_separator(None) { Some(self.prev_token.span) } else { None };
+
         // Parse the first pattern (`p_0`).
-        let first_pat = self.parse_pat(expected)?;
+        let first_pat = self.parse_pat_no_top_alt(expected)?;
         self.maybe_recover_unexpected_comma(first_pat.span, rc, gate_or)?;
 
         // If the next token is not a `|`,
         // this is not an or-pattern and we should exit here.
         if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
+            // If we parsed a leading `|` which should be gated,
+            // then we should really gate the leading `|`.
+            // This complicated procedure is done purely for diagnostics UX.
+            if let Some(leading_vert_span) = leading_vert_span {
+                if gate_or == GateOr::Yes && self.sess.gated_spans.is_ungated(sym::or_patterns) {
+                    self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
+                }
+
+                // If there was a leading vert, treat this as an or-pattern. This improves
+                // diagnostics.
+                let span = leading_vert_span.to(self.prev_token.span);
+                return Ok(self.mk_pat(span, PatKind::Or(vec![first_pat])));
+            }
+
             return Ok(first_pat);
         }
 
         // Parse the patterns `p_1 | ... | p_n` where `n > 0`.
-        let lo = first_pat.span;
+        let lo = leading_vert_span.unwrap_or(first_pat.span);
         let mut pats = vec![first_pat];
         while self.eat_or_separator(Some(lo)) {
-            let pat = self.parse_pat(expected).map_err(|mut err| {
+            let pat = self.parse_pat_no_top_alt(expected).map_err(|mut err| {
                 err.span_label(lo, WHILE_PARSING_OR_MSG);
                 err
             })?;
@@ -127,6 +104,62 @@ impl<'a> Parser<'a> {
         Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
     }
 
+    /// Parse the pattern for a function or function pointer parameter.
+    pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
+        // We actually do _not_ allow top-level or-patterns in function params, but we use
+        // `parse_pat_allow_top_alt` anyway so that we can detect when a user tries to use it. This
+        // allows us to print a better error message.
+        //
+        // In order to get good UX, we first recover in the case of a leading vert for an illegal
+        // top-level or-pat. Normally, this means recovering both `|` and `||`, but in this case,
+        // a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
+        // separately.
+        if let token::OrOr = self.token.kind {
+            let span = self.token.span;
+            let mut err = self.struct_span_err(span, "unexpected `||` before function parameter");
+            err.span_suggestion(
+                span,
+                "remove the `||`",
+                String::new(),
+                Applicability::MachineApplicable,
+            );
+            err.note("alternatives in or-patterns are separated with `|`, not `||`");
+            err.emit();
+            self.bump();
+        }
+
+        let pat = self.parse_pat_allow_top_alt(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
+
+        if let PatKind::Or(..) = &pat.kind {
+            self.ban_illegal_fn_param_or_pat(&pat);
+        }
+
+        Ok(pat)
+    }
+
+    /// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
+    fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
+        // If all we have a leading vert, then print a special message. This is the case if
+        // `parse_pat_allow_top_alt` returns an or-pattern with one variant.
+        let (msg, fix) = match &pat.kind {
+            PatKind::Or(pats) if pats.len() == 1 => {
+                let msg = "remove the leading `|`";
+                let fix = pprust::pat_to_string(pat);
+                (msg, fix)
+            }
+
+            _ => {
+                let msg = "wrap the pattern in parentheses";
+                let fix = format!("({})", pprust::pat_to_string(pat));
+                (msg, fix)
+            }
+        };
+
+        self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parentheses")
+            .span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
+            .emit();
+    }
+
     /// Eat the or-pattern `|` separator.
     /// If instead a `||` token is encountered, recover and pretend we parsed `|`.
     fn eat_or_separator(&mut self, lo: Option<Span>) -> bool {
@@ -179,7 +212,7 @@ impl<'a> Parser<'a> {
 
     /// We have parsed `||` instead of `|`. Error and suggest `|` instead.
     fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
-        let mut err = self.struct_span_err(self.token.span, "unexpected token `||` after pattern");
+        let mut err = self.struct_span_err(self.token.span, "unexpected token `||` in pattern");
         err.span_suggestion(
             self.token.span,
             "use a single `|` to separate multiple alternative patterns",
@@ -244,7 +277,7 @@ impl<'a> Parser<'a> {
     /// sequence of patterns until `)` is reached.
     fn skip_pat_list(&mut self) -> PResult<'a, ()> {
         while !self.check(&token::CloseDelim(token::Paren)) {
-            self.parse_pat(None)?;
+            self.parse_pat_no_top_alt(None)?;
             if !self.eat(&token::Comma) {
                 return Ok(());
             }
@@ -252,22 +285,6 @@ impl<'a> Parser<'a> {
         Ok(())
     }
 
-    /// Recursive possibly-or-pattern parser with recovery for an erroneous leading `|`.
-    /// See `parse_pat_with_or` for details on parsing or-patterns.
-    fn parse_pat_with_or_inner(&mut self) -> PResult<'a, P<Pat>> {
-        self.recover_leading_vert(None, "only allowed in a top-level pattern");
-        self.parse_pat_with_or(None, GateOr::Yes, RecoverComma::No)
-    }
-
-    /// Recover if `|` or `||` is here.
-    /// The user is thinking that a leading `|` is allowed in this position.
-    fn recover_leading_vert(&mut self, lo: Option<Span>, ctx: &str) {
-        if let token::BinOp(token::Or) | token::OrOr = self.token.kind {
-            self.ban_illegal_vert(lo, "leading", ctx);
-            self.bump();
-        }
-    }
-
     /// A `|` or possibly `||` token shouldn't be here. Ban it.
     fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
         let span = self.token.span;
@@ -305,8 +322,9 @@ impl<'a> Parser<'a> {
             self.parse_pat_tuple_or_parens()?
         } else if self.check(&token::OpenDelim(token::Bracket)) {
             // Parse `[pat, pat,...]` as a slice pattern.
-            let (pats, _) =
+            let (pats, _) = self.parse_delim_comma_seq(token::Bracket, |p| {
-                self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat_with_or_inner())?;
+                p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
+            })?;
             PatKind::Slice(pats)
         } else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
             // A rest pattern `..`.
@@ -429,7 +447,7 @@ impl<'a> Parser<'a> {
 
         // At this point we attempt to parse `@ $pat_rhs` and emit an error.
         self.bump(); // `@`
-        let mut rhs = self.parse_pat(None)?;
+        let mut rhs = self.parse_pat_no_top_alt(None)?;
         let sp = lhs.span.to(rhs.span);
 
         if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
@@ -518,8 +536,9 @@ impl<'a> Parser<'a> {
 
     /// Parse a tuple or parenthesis pattern.
     fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
-        let (fields, trailing_comma) =
+        let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
-            self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
+            p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
+        })?;
 
         // Here, `(pat,)` is a tuple pattern.
         // For backward compatibility, `(..)` is a tuple pattern as well.
@@ -548,7 +567,7 @@ impl<'a> Parser<'a> {
         }
 
         // Parse the pattern we hope to be an identifier.
-        let mut pat = self.parse_pat(Some("identifier"))?;
+        let mut pat = self.parse_pat_no_top_alt(Some("identifier"))?;
 
         // If we don't have `mut $ident (@ pat)?`, error.
         if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind {
@@ -793,7 +812,7 @@ impl<'a> Parser<'a> {
     fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
         let ident = self.parse_ident()?;
         let sub = if self.eat(&token::At) {
-            Some(self.parse_pat(Some("binding pattern"))?)
+            Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
         } else {
             None
         };
@@ -832,7 +851,9 @@ impl<'a> Parser<'a> {
         if qself.is_some() {
             return self.error_qpath_before_pat(&path, "(");
         }
-        let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
+        let (fields, _) = self.parse_paren_comma_seq(|p| {
+            p.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)
+        })?;
         Ok(PatKind::TupleStruct(path, fields))
     }
 
@@ -998,7 +1019,7 @@ impl<'a> Parser<'a> {
             // Parsing a pattern of the form `fieldname: pat`.
             let fieldname = self.parse_field_name()?;
             self.bump();
-            let pat = self.parse_pat_with_or_inner()?;
+            let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)?;
             hi = pat.span;
             (pat, fieldname, false)
         } else {

compiler/rustc_parse/src/parser/stmt.rs

@@ -220,7 +220,7 @@ impl<'a> Parser<'a> {
     /// Parses a local variable declaration.
     fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
         let lo = self.prev_token.span;
-        let pat = self.parse_top_pat(GateOr::Yes, RecoverComma::Yes)?;
+        let pat = self.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::Yes)?;
 
         let (err, ty) = if self.eat(&token::Colon) {
             // Save the state of the parser before parsing type normally, in case there is a `:`

src/test/ui/or-patterns/feature-gate-or_patterns.stderr

@@ -8,10 +8,10 @@ LL |         Some(0 | 1 | 2) => {}
    = help: add `#![feature(or_patterns)]` to the crate attributes to enable
 
 error[E0658]: or-patterns syntax is experimental
-  --> $DIR/feature-gate-or_patterns.rs:28:11
+  --> $DIR/feature-gate-or_patterns.rs:28:9
    |
 LL |     let | A | B;
-   |           ^^^^^
+   |         ^^^^^^^
    |
    = note: see issue #54883 <https://github.com/rust-lang/rust/issues/54883> for more information
    = help: add `#![feature(or_patterns)]` to the crate attributes to enable
@@ -26,10 +26,10 @@ LL |     let A | B;
    = help: add `#![feature(or_patterns)]` to the crate attributes to enable
 
 error[E0658]: or-patterns syntax is experimental
-  --> $DIR/feature-gate-or_patterns.rs:30:11
+  --> $DIR/feature-gate-or_patterns.rs:30:9
    |
 LL |     for | A | B in 0 {}
-   |           ^^^^^
+   |         ^^^^^^^
    |
    = note: see issue #54883 <https://github.com/rust-lang/rust/issues/54883> for more information
    = help: add `#![feature(or_patterns)]` to the crate attributes to enable

src/test/ui/or-patterns/fn-param-wrap-parens.fixed

@@ -11,4 +11,4 @@ enum E { A, B }
 use E::*;
 
 #[cfg(FALSE)]
-fn fun1((A | B): E) {} //~ ERROR an or-pattern parameter must be wrapped in parenthesis
+fn fun1((A | B): E) {} //~ ERROR an or-pattern parameter must be wrapped in parentheses

src/test/ui/or-patterns/fn-param-wrap-parens.rs

@@ -11,4 +11,4 @@ enum E { A, B }
 use E::*;
 
 #[cfg(FALSE)]
-fn fun1(A | B: E) {} //~ ERROR an or-pattern parameter must be wrapped in parenthesis
+fn fun1(A | B: E) {} //~ ERROR an or-pattern parameter must be wrapped in parentheses

src/test/ui/or-patterns/fn-param-wrap-parens.stderr

@@ -1,8 +1,8 @@
-error: an or-pattern parameter must be wrapped in parenthesis
+error: an or-pattern parameter must be wrapped in parentheses
   --> $DIR/fn-param-wrap-parens.rs:14:9
    |
 LL | fn fun1(A | B: E) {}
-   |         ^^^^^ help: wrap the pattern in parenthesis: `(A | B)`
+   |         ^^^^^ help: wrap the pattern in parentheses: `(A | B)`
 
 error: aborting due to previous error
 

src/test/ui/or-patterns/multiple-pattern-typo.rs

@@ -4,41 +4,41 @@ fn main() {
     let x = 3;
 
     match x {
-        1 | 2 || 3 => (), //~ ERROR unexpected token `||` after pattern
+        1 | 2 || 3 => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     match x {
-        (1 | 2 || 3) => (), //~ ERROR unexpected token `||` after pattern
+        (1 | 2 || 3) => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     match (x,) {
-        (1 | 2 || 3,) => (), //~ ERROR unexpected token `||` after pattern
+        (1 | 2 || 3,) => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     struct TS(u8);
 
     match TS(x) {
-        TS(1 | 2 || 3) => (), //~ ERROR unexpected token `||` after pattern
+        TS(1 | 2 || 3) => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     struct NS { f: u8 }
 
     match (NS { f: x }) {
-        NS { f: 1 | 2 || 3 } => (), //~ ERROR unexpected token `||` after pattern
+        NS { f: 1 | 2 || 3 } => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     match [x] {
-        [1 | 2 || 3] => (), //~ ERROR unexpected token `||` after pattern
+        [1 | 2 || 3] => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 
     match x {
-        || 1 | 2 | 3 => (), //~ ERROR unexpected token `||` after pattern
+        || 1 | 2 | 3 => (), //~ ERROR unexpected token `||` in pattern
         _ => (),
     }
 }

src/test/ui/or-patterns/multiple-pattern-typo.stderr

@@ -1,4 +1,4 @@
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:7:15
    |
 LL |         1 | 2 || 3 => (),
@@ -6,7 +6,7 @@ LL |         1 | 2 || 3 => (),
    |         |
    |         while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:12:16
    |
 LL |         (1 | 2 || 3) => (),
@@ -14,7 +14,7 @@ LL |         (1 | 2 || 3) => (),
    |          |
    |          while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:17:16
    |
 LL |         (1 | 2 || 3,) => (),
@@ -22,7 +22,7 @@ LL |         (1 | 2 || 3,) => (),
    |          |
    |          while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:24:18
    |
 LL |         TS(1 | 2 || 3) => (),
@@ -30,7 +30,7 @@ LL |         TS(1 | 2 || 3) => (),
    |            |
    |            while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:31:23
    |
 LL |         NS { f: 1 | 2 || 3 } => (),
@@ -38,7 +38,7 @@ LL |         NS { f: 1 | 2 || 3 } => (),
    |                 |
    |                 while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:36:16
    |
 LL |         [1 | 2 || 3] => (),
@@ -46,7 +46,7 @@ LL |         [1 | 2 || 3] => (),
    |          |
    |          while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/multiple-pattern-typo.rs:41:9
    |
 LL |         || 1 | 2 | 3 => (),

src/test/ui/or-patterns/or-patterns-syntactic-fail.rs

@@ -14,29 +14,8 @@ fn no_top_level_or_patterns() {
     //           -------- This looks like an or-pattern but is in fact `|A| (B: E | ())`.
 
     // ...and for now neither do we allow or-patterns at the top level of functions.
-    fn fun1(A | B: E) {} //~ ERROR an or-pattern parameter must be wrapped in parenthesis
+    fn fun1(A | B: E) {} //~ ERROR an or-pattern parameter must be wrapped in parentheses
 
     fn fun2(| A | B: E) {}
-    //~^ ERROR a leading `|` is not allowed in a parameter pattern
+    //~^ ERROR an or-pattern parameter must be wrapped in parentheses
-    //~| ERROR an or-pattern parameter must be wrapped in parenthesis
-}
-
-// We also do not allow a leading `|` when not in a top level position:
-
-fn no_leading_inner() {
-    struct TS(E);
-    struct NS { f: E }
-
-    let ( | A | B) = E::A; //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let ( | A | B,) = (E::B,); //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let [ | A | B ] = [E::A]; //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let TS( | A | B ); //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let NS { f: | A | B }; //~ ERROR a leading `|` is only allowed in a top-level pattern
-
-    let ( || A | B) = E::A; //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let [ || A | B ] = [E::A]; //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let TS( || A | B ); //~ ERROR a leading `|` is only allowed in a top-level pattern
-    let NS { f: || A | B }; //~ ERROR a leading `|` is only allowed in a top-level pattern
-
-    let recovery_witness: String = 0; //~ ERROR mismatched types
 }

src/test/ui/or-patterns/or-patterns-syntactic-fail.stderr

@@ -1,82 +1,14 @@
-error: an or-pattern parameter must be wrapped in parenthesis
+error: an or-pattern parameter must be wrapped in parentheses
   --> $DIR/or-patterns-syntactic-fail.rs:17:13
    |
 LL |     fn fun1(A | B: E) {}
-   |             ^^^^^ help: wrap the pattern in parenthesis: `(A | B)`
+   |             ^^^^^ help: wrap the pattern in parentheses: `(A | B)`
 
-error: a leading `|` is not allowed in a parameter pattern
+error: an or-pattern parameter must be wrapped in parentheses
   --> $DIR/or-patterns-syntactic-fail.rs:19:13
    |
 LL |     fn fun2(| A | B: E) {}
-   |             ^ help: remove the `|`
+   |             ^^^^^^^ help: wrap the pattern in parentheses: `(A | B)`
-
-error: an or-pattern parameter must be wrapped in parenthesis
-  --> $DIR/or-patterns-syntactic-fail.rs:19:15
-   |
-LL |     fn fun2(| A | B: E) {}
-   |               ^^^^^ help: wrap the pattern in parenthesis: `(A | B)`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:30:11
-   |
-LL |     let ( | A | B) = E::A;
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:31:11
-   |
-LL |     let ( | A | B,) = (E::B,);
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:32:11
-   |
-LL |     let [ | A | B ] = [E::A];
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:33:13
-   |
-LL |     let TS( | A | B );
-   |             ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:34:17
-   |
-LL |     let NS { f: | A | B };
-   |                 ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:36:11
-   |
-LL |     let ( || A | B) = E::A;
-   |           ^^ help: remove the `||`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:37:11
-   |
-LL |     let [ || A | B ] = [E::A];
-   |           ^^ help: remove the `||`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:38:13
-   |
-LL |     let TS( || A | B );
-   |             ^^ help: remove the `||`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/or-patterns-syntactic-fail.rs:39:17
-   |
-LL |     let NS { f: || A | B };
-   |                 ^^ help: remove the `||`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
 
 error[E0369]: no implementation for `E | ()`
   --> $DIR/or-patterns-syntactic-fail.rs:13:22
@@ -88,17 +20,6 @@ LL |     let _ = |A | B: E| ();
    |
    = note: an implementation of `std::ops::BitOr` might be missing for `E`
 
-error[E0308]: mismatched types
+error: aborting due to 3 previous errors
-  --> $DIR/or-patterns-syntactic-fail.rs:41:36
-   |
-LL |     let recovery_witness: String = 0;
-   |                           ------   ^
-   |                           |        |
-   |                           |        expected struct `String`, found integer
-   |                           |        help: try using a conversion method: `0.to_string()`
-   |                           expected due to this
 
-error: aborting due to 14 previous errors
+For more information about this error, try `rustc --explain E0369`.
-
-Some errors have detailed explanations: E0308, E0369.
-For more information about an error, try `rustc --explain E0308`.

src/test/ui/or-patterns/remove-leading-vert.fixed

@@ -9,17 +9,17 @@ fn main() {}
 
 #[cfg(FALSE)]
 fn leading() {
-    fn fun1(  A: E) {} //~ ERROR a leading `|` is not allowed in a parameter pattern
+    fn fun1( A: E) {} //~ ERROR an or-pattern parameter must be wrapped in parentheses
-    fn fun2(  A: E) {} //~ ERROR a leading `|` is not allowed in a parameter pattern
+    fn fun2(  A: E) {} //~ ERROR unexpected `||` before function parameter
-    let (  A): E; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( | A): E;
-    let (  A): (E); //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( | A): (E); //~ ERROR unexpected token `||` in pattern
-    let (  A,): (E,); //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( | A,): (E,);
-    let [  A ]: [E; 1]; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let [ | A ]: [E; 1];
-    let [  A ]: [E; 1]; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let [ | A ]: [E; 1]; //~ ERROR unexpected token `||` in pattern
-    let TS(  A ): TS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let TS( | A ): TS;
-    let TS(  A ): TS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let TS( | A ): TS; //~ ERROR unexpected token `||` in pattern
-    let NS { f:  A }: NS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let NS { f: | A }: NS;
-    let NS { f:  A }: NS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let NS { f: | A }: NS; //~ ERROR unexpected token `||` in pattern
 }
 
 #[cfg(FALSE)]
@@ -29,12 +29,12 @@ fn trailing() {
     let ( A | B  ): E; //~ ERROR a trailing `|` is not allowed in an or-pattern
     let [ A | B  ]: [E; 1]; //~ ERROR a trailing `|` is not allowed in an or-pattern
     let S { f: B  }; //~ ERROR a trailing `|` is not allowed in an or-pattern
-    let ( A | B  ): E; //~ ERROR unexpected token `||` after pattern
+    let ( A | B  ): E; //~ ERROR unexpected token `||` in pattern
     //~^ ERROR a trailing `|` is not allowed in an or-pattern
     match A {
         A  => {} //~ ERROR a trailing `|` is not allowed in an or-pattern
         A  => {} //~ ERROR a trailing `|` is not allowed in an or-pattern
-        A | B  => {} //~ ERROR unexpected token `||` after pattern
+        A | B  => {} //~ ERROR unexpected token `||` in pattern
         //~^ ERROR a trailing `|` is not allowed in an or-pattern
         | A | B  => {}
         //~^ ERROR a trailing `|` is not allowed in an or-pattern

src/test/ui/or-patterns/remove-leading-vert.rs

@@ -9,17 +9,17 @@ fn main() {}
 
 #[cfg(FALSE)]
 fn leading() {
-    fn fun1( | A: E) {} //~ ERROR a leading `|` is not allowed in a parameter pattern
+    fn fun1( | A: E) {} //~ ERROR an or-pattern parameter must be wrapped in parentheses
-    fn fun2( || A: E) {} //~ ERROR a leading `|` is not allowed in a parameter pattern
+    fn fun2( || A: E) {} //~ ERROR unexpected `||` before function parameter
-    let ( | A): E; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( | A): E;
-    let ( || A): (E); //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( || A): (E); //~ ERROR unexpected token `||` in pattern
-    let ( | A,): (E,); //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let ( | A,): (E,);
-    let [ | A ]: [E; 1]; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let [ | A ]: [E; 1];
-    let [ || A ]: [E; 1]; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let [ || A ]: [E; 1]; //~ ERROR unexpected token `||` in pattern
-    let TS( | A ): TS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let TS( | A ): TS;
-    let TS( || A ): TS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let TS( || A ): TS; //~ ERROR unexpected token `||` in pattern
-    let NS { f: | A }: NS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let NS { f: | A }: NS;
-    let NS { f: || A }: NS; //~ ERROR a leading `|` is only allowed in a top-level pattern
+    let NS { f: || A }: NS; //~ ERROR unexpected token `||` in pattern
 }
 
 #[cfg(FALSE)]
@@ -29,12 +29,12 @@ fn trailing() {
     let ( A | B | ): E; //~ ERROR a trailing `|` is not allowed in an or-pattern
     let [ A | B | ]: [E; 1]; //~ ERROR a trailing `|` is not allowed in an or-pattern
     let S { f: B | }; //~ ERROR a trailing `|` is not allowed in an or-pattern
-    let ( A || B | ): E; //~ ERROR unexpected token `||` after pattern
+    let ( A || B | ): E; //~ ERROR unexpected token `||` in pattern
     //~^ ERROR a trailing `|` is not allowed in an or-pattern
     match A {
         A | => {} //~ ERROR a trailing `|` is not allowed in an or-pattern
         A || => {} //~ ERROR a trailing `|` is not allowed in an or-pattern
-        A || B | => {} //~ ERROR unexpected token `||` after pattern
+        A || B | => {} //~ ERROR unexpected token `||` in pattern
         //~^ ERROR a trailing `|` is not allowed in an or-pattern
         | A | B | => {}
         //~^ ERROR a trailing `|` is not allowed in an or-pattern

src/test/ui/or-patterns/remove-leading-vert.stderr

@@ -1,10 +1,10 @@
-error: a leading `|` is not allowed in a parameter pattern
+error: an or-pattern parameter must be wrapped in parentheses
   --> $DIR/remove-leading-vert.rs:12:14
    |
 LL |     fn fun1( | A: E) {}
-   |              ^ help: remove the `|`
+   |              ^^^ help: remove the leading `|`: `A`
 
-error: a leading `|` is not allowed in a parameter pattern
+error: unexpected `||` before function parameter
   --> $DIR/remove-leading-vert.rs:13:14
    |
 LL |     fn fun2( || A: E) {}
@@ -12,67 +12,29 @@ LL |     fn fun2( || A: E) {}
    |
    = note: alternatives in or-patterns are separated with `|`, not `||`
 
-error: a leading `|` is only allowed in a top-level pattern
+error: unexpected token `||` in pattern
-  --> $DIR/remove-leading-vert.rs:14:11
-   |
-LL |     let ( | A): E;
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
   --> $DIR/remove-leading-vert.rs:15:11
    |
 LL |     let ( || A): (E);
-   |           ^^ help: remove the `||`
+   |           ^^ help: use a single `|` to separate multiple alternative patterns: `|`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
 
-error: a leading `|` is only allowed in a top-level pattern
+error: unexpected token `||` in pattern
-  --> $DIR/remove-leading-vert.rs:16:11
-   |
-LL |     let ( | A,): (E,);
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
-  --> $DIR/remove-leading-vert.rs:17:11
-   |
-LL |     let [ | A ]: [E; 1];
-   |           ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
   --> $DIR/remove-leading-vert.rs:18:11
    |
 LL |     let [ || A ]: [E; 1];
-   |           ^^ help: remove the `||`
+   |           ^^ help: use a single `|` to separate multiple alternative patterns: `|`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
 
-error: a leading `|` is only allowed in a top-level pattern
+error: unexpected token `||` in pattern
-  --> $DIR/remove-leading-vert.rs:19:13
-   |
-LL |     let TS( | A ): TS;
-   |             ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
   --> $DIR/remove-leading-vert.rs:20:13
    |
 LL |     let TS( || A ): TS;
-   |             ^^ help: remove the `||`
+   |             ^^ help: use a single `|` to separate multiple alternative patterns: `|`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
 
-error: a leading `|` is only allowed in a top-level pattern
+error: unexpected token `||` in pattern
-  --> $DIR/remove-leading-vert.rs:21:17
-   |
-LL |     let NS { f: | A }: NS;
-   |                 ^ help: remove the `|`
-
-error: a leading `|` is only allowed in a top-level pattern
   --> $DIR/remove-leading-vert.rs:22:17
    |
 LL |     let NS { f: || A }: NS;
-   |                 ^^ help: remove the `||`
+   |                 ^^ help: use a single `|` to separate multiple alternative patterns: `|`
-   |
-   = note: alternatives in or-patterns are separated with `|`, not `||`
 
 error: a trailing `|` is not allowed in an or-pattern
   --> $DIR/remove-leading-vert.rs:27:13
@@ -114,7 +76,7 @@ LL |     let S { f: B | };
    |                |
    |                while parsing this or-pattern starting here
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/remove-leading-vert.rs:32:13
    |
 LL |     let ( A || B | ): E;
@@ -148,7 +110,7 @@ LL |         A || => {}
    |
    = note: alternatives in or-patterns are separated with `|`, not `||`
 
-error: unexpected token `||` after pattern
+error: unexpected token `||` in pattern
   --> $DIR/remove-leading-vert.rs:37:11
    |
 LL |         A || B | => {}
@@ -196,5 +158,5 @@ LL |     let a | ;
    |         |
    |         while parsing this or-pattern starting here
 
-error: aborting due to 26 previous errors
+error: aborting due to 21 previous errors