parser: gracefully handle fn foo(A | B: type).

Author: Centril

src/libsyntax/parse/parser.rs

@@ -988,7 +988,7 @@ impl<'a> Parser<'a> {
         let (pat, ty) = if is_name_required || self.is_named_argument() {
             debug!("parse_arg_general parse_pat (is_name_required:{})", is_name_required);
 
-            let pat = self.parse_pat(Some("argument name"))?;
+            let pat = self.parse_fn_param_pat()?;
             if let Err(mut err) = self.expect(&token::Colon) {
                 if let Some(ident) = self.argument_without_type(
                     &mut err,

src/libsyntax/parse/parser/expr.rs

@@ -1,7 +1,7 @@
 use super::{Parser, PResult, Restrictions, PrevTokenKind, TokenType, PathStyle};
 use super::{BlockMode, SemiColonMode};
 use super::{SeqSep, TokenExpectType};
-use super::pat::GateOr;
+use super::pat::{GateOr, PARAM_EXPECTED};
 
 use crate::maybe_recover_from_interpolated_ty_qpath;
 use crate::ptr::P;
@@ -1176,7 +1176,7 @@ impl<'a> Parser<'a> {
     fn parse_fn_block_arg(&mut self) -> PResult<'a, Arg> {
         let lo = self.token.span;
         let attrs = self.parse_arg_attributes()?;
-        let pat = self.parse_pat(Some("argument name"))?;
+        let pat = self.parse_pat(PARAM_EXPECTED)?;
         let t = if self.eat(&token::Colon) {
             self.parse_ty()?
         } else {

src/libsyntax/parse/parser/pat.rs

@@ -14,6 +14,9 @@ use errors::{Applicability, DiagnosticBuilder};
 
 type Expected = Option<&'static str>;
 
+/// `Expected` for function and lambda parameter patterns.
+pub(super) const PARAM_EXPECTED: Expected = Some("parameter name");
+
 /// Whether or not an or-pattern should be gated when occurring in the current context.
 #[derive(PartialEq)]
 pub enum GateOr { Yes, No }
@@ -49,7 +52,7 @@ impl<'a> Parser<'a> {
         let gated_leading_vert = self.eat_or_separator() && gate_or == GateOr::Yes;
 
         // Parse the possibly-or-pattern.
-        let pat = self.parse_pat_with_or(gate_or, TopLevel::Yes)?;
+        let pat = self.parse_pat_with_or(None, gate_or, TopLevel::Yes)?;
 
         // If we parsed a leading `|` which should be gated,
         // and no other gated or-pattern has been parsed thus far,
@@ -65,11 +68,38 @@ impl<'a> Parser<'a> {
         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("not allowed in a parameter pattern");
+        let pat = self.parse_pat_with_or(PARAM_EXPECTED, GateOr::No, TopLevel::No)?;
+
+        if let PatKind::Or(..) = &pat.node {
+            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, gate_or: GateOr, top_level: TopLevel) -> PResult<'a, P<Pat>> {
+    fn parse_pat_with_or(
+        &mut self,
+        expected: Expected,
+        gate_or: GateOr,
+        top_level: TopLevel,
+    ) -> PResult<'a, P<Pat>> {
         // Parse the first pattern.
-        let first_pat = self.parse_pat(None)?;
+        let first_pat = self.parse_pat(expected)?;
         self.maybe_recover_unexpected_comma(first_pat.span, top_level)?;
 
         // If the next token is not a `|`,
@@ -81,7 +111,7 @@ impl<'a> Parser<'a> {
         let lo = first_pat.span;
         let mut pats = vec![first_pat];
         while self.eat_or_separator() {
-            let pat = self.parse_pat(None).map_err(|mut err| {
+            let pat = self.parse_pat(expected).map_err(|mut err| {
                 err.span_label(lo, "while parsing this or-pattern staring here");
                 err
             })?;
@@ -176,18 +206,18 @@ impl<'a> Parser<'a> {
     /// 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_inner_leading_vert();
-        self.parse_pat_with_or(GateOr::Yes, TopLevel::No)
+        self.recover_leading_vert("only allowed in a top-level pattern");
+        self.parse_pat_with_or(None, GateOr::Yes, TopLevel::No)
     }
 
     /// Recover if `|` or `||` is here.
     /// The user is thinking that a leading `|` is allowed in this position.
-    fn recover_inner_leading_vert(&mut self) {
+    fn recover_leading_vert(&mut self, ctx: &str) {
         if let token::BinOp(token::Or) | token::OrOr = self.token.kind {
             let span = self.token.span;
             let rm_msg = format!("remove the `{}`", pprust::token_to_string(&self.token));
 
-            self.struct_span_err(span, "a leading `|` is only allowed in a top-level pattern")
+            self.struct_span_err(span, &format!("a leading `|` is {}", ctx))
                 .span_suggestion(span, &rm_msg, String::new(), Applicability::MachineApplicable)
                 .emit();
 

src/test/ui/anon-params-denied-2018.rs

@@ -3,7 +3,7 @@
 // edition:2018
 
 trait T {
-    fn foo(i32); //~ expected one of `:` or `@`, found `)`
+    fn foo(i32); //~ expected one of `:`, `@`, or `|`, found `)`
 
     fn bar_with_default_impl(String, String) {}
     //~^ ERROR expected one of `:`

src/test/ui/anon-params-denied-2018.stderr

@@ -1,8 +1,8 @@
-error: expected one of `:` or `@`, found `)`
+error: expected one of `:`, `@`, or `|`, found `)`
   --> $DIR/anon-params-denied-2018.rs:6:15
    |
 LL |     fn foo(i32);
-   |               ^ expected one of `:` or `@` here
+   |               ^ expected one of `:`, `@`, or `|` here
    |
    = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
 help: if this was a parameter name, give it a type
@@ -14,11 +14,11 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn foo(_: i32);
    |            ^^^^^^
 
-error: expected one of `:` or `@`, found `,`
+error: expected one of `:`, `@`, or `|`, found `,`
   --> $DIR/anon-params-denied-2018.rs:8:36
    |
 LL |     fn bar_with_default_impl(String, String) {}
-   |                                    ^ expected one of `:` or `@` here
+   |                                    ^ expected one of `:`, `@`, or `|` here
    |
    = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
 help: if this was a parameter name, give it a type
@@ -30,11 +30,11 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn bar_with_default_impl(_: String, String) {}
    |                              ^^^^^^^^^
 
-error: expected one of `:` or `@`, found `)`
+error: expected one of `:`, `@`, or `|`, found `)`
   --> $DIR/anon-params-denied-2018.rs:8:44
    |
 LL |     fn bar_with_default_impl(String, String) {}
-   |                                            ^ expected one of `:` or `@` here
+   |                                            ^ expected one of `:`, `@`, or `|` here
    |
    = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
 help: if this was a parameter name, give it a type
@@ -46,11 +46,11 @@ help: if this is a type, explicitly ignore the parameter name
 LL |     fn bar_with_default_impl(String, _: String) {}
    |                                      ^^^^^^^^^
 
-error: expected one of `:` or `@`, found `,`
+error: expected one of `:`, `@`, or `|`, found `,`
   --> $DIR/anon-params-denied-2018.rs:13:22
    |
 LL |     fn baz(a:usize, b, c: usize) -> usize {
-   |                      ^ expected one of `:` or `@` here
+   |                      ^ expected one of `:`, `@`, or `|` here
    |
    = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
 help: if this was a parameter name, give it a type

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

@@ -25,7 +25,11 @@ 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 fun(A | B: E) {} //~ ERROR expected one of `:` or `@`, found `|`
+    fn fun1(A | B: E) {} //~ ERROR an or-pattern parameter must be wrapped in parenthesis
+
+    fn fun2(| A | B: E) {}
+    //~^ ERROR a leading `|` is not allowed in a parameter pattern
+    //~| ERROR an or-pattern parameter must be wrapped in parenthesis
 }
 
 // We also do not allow a leading `|` when not in a top level position:

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

@@ -1,59 +1,71 @@
-error: expected one of `:` or `@`, found `|`
-  --> $DIR/or-patterns-syntactic-fail.rs:28:14
+error: an or-pattern parameter must be wrapped in parenthesis
+  --> $DIR/or-patterns-syntactic-fail.rs:28:13
    |
-LL |     fn fun(A | B: E) {}
-   |              ^ expected one of `:` or `@` here
+LL |     fn fun1(A | B: E) {}
+   |             ^^^^^ help: wrap the pattern in parenthesis: `(A | B)`
+
+error: a leading `|` is not allowed in a parameter pattern
+  --> $DIR/or-patterns-syntactic-fail.rs:30:13
+   |
+LL |     fn fun2(| A | B: E) {}
+   |             ^ help: remove the `|`
+
+error: an or-pattern parameter must be wrapped in parenthesis
+  --> $DIR/or-patterns-syntactic-fail.rs:30:15
+   |
+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:37:11
+  --> $DIR/or-patterns-syntactic-fail.rs:41:11
    |
 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:38:11
+  --> $DIR/or-patterns-syntactic-fail.rs:42:11
    |
 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:39:11
+  --> $DIR/or-patterns-syntactic-fail.rs:43:11
    |
 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:40:13
+  --> $DIR/or-patterns-syntactic-fail.rs:44:13
    |
 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:41:17
+  --> $DIR/or-patterns-syntactic-fail.rs:45:17
    |
 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:43:11
+  --> $DIR/or-patterns-syntactic-fail.rs:47:11
    |
 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:44:11
+  --> $DIR/or-patterns-syntactic-fail.rs:48:11
    |
 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:45:13
+  --> $DIR/or-patterns-syntactic-fail.rs:49:13
    |
 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:46:17
+  --> $DIR/or-patterns-syntactic-fail.rs:50:17
    |
 LL |     let NS { f: || A | B };
    |                 ^^ help: remove the `||`
@@ -95,7 +107,7 @@ LL |     let _ = |A | B: E| ();
    = note: an implementation of `std::ops::BitOr` might be missing for `E`
 
 error[E0308]: mismatched types
-  --> $DIR/or-patterns-syntactic-fail.rs:48:36
+  --> $DIR/or-patterns-syntactic-fail.rs:52:36
    |
 LL |     let recovery_witness: String = 0;
    |                                    ^
@@ -106,7 +118,7 @@ LL |     let recovery_witness: String = 0;
    = note: expected type `std::string::String`
               found type `{integer}`
 
-error: aborting due to 14 previous errors
+error: aborting due to 16 previous errors
 
 Some errors have detailed explanations: E0308, E0369.
 For more information about an error, try `rustc --explain E0308`.

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

@@ -2,29 +2,29 @@ struct S;
 
 impl S {
     fn foo(&self, &str bar) {}
-    //~^ ERROR expected one of `:` or `@`
+    //~^ ERROR expected one of `:`, `@`
     //~| HELP declare the type after the parameter binding
     //~| SUGGESTION <identifier>: <type>
 }
 
 fn baz(S quux, xyzzy: i32) {}
-//~^ ERROR expected one of `:` or `@`
+//~^ ERROR expected one of `:`, `@`
 //~| HELP declare the type after the parameter binding
 //~| SUGGESTION <identifier>: <type>
 
 fn one(i32 a b) {}
-//~^ ERROR expected one of `:` or `@`
+//~^ ERROR expected one of `:`, `@`
 
 fn pattern((i32, i32) (a, b)) {}
-//~^ ERROR expected `:`
+//~^ ERROR expected one of `:`
 
 fn fizz(i32) {}
-//~^ ERROR expected one of `:` or `@`
+//~^ ERROR expected one of `:`, `@`
 //~| HELP if this was a parameter name, give it a type
 //~| HELP if this is a type, explicitly ignore the parameter name
 
 fn missing_colon(quux S) {}
-//~^ ERROR expected one of `:` or `@`
+//~^ ERROR expected one of `:`, `@`
 //~| HELP declare the type after the parameter binding
 //~| SUGGESTION <identifier>: <type>