Rollup merge of #145378 - xizheyin:144968, r=davidtwco

Add `FnContext` in parser for diagnostic

Fixes #144968

Inspired by #144968 (comment), I implemented `FnContext` to indicate whether a function should have a self parameter, for example, whether the function is a trait method, whether it is in an impl block. And I removed the outdated note.

I made two commits to show the difference.

cc `@estebank` `@djc`

r? compiler

Author: Zalathar

compiler/rustc_parse/src/parser/attr.rs

@@ -11,6 +11,7 @@ use tracing::debug;
 use super::{
     AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle, Trailing, UsePreAttrPos,
 };
+use crate::parser::FnContext;
 use crate::{errors, exp, fluent_generated as fluent};
 
 // Public for rustfmt usage
@@ -200,7 +201,7 @@ impl<'a> Parser<'a> {
             AttrWrapper::empty(),
             true,
             false,
-            FnParseMode { req_name: |_| true, req_body: true },
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true },
             ForceCollect::No,
         ) {
             Ok(Some(item)) => {

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -44,6 +44,7 @@ use crate::errors::{
     UnexpectedConstParamDeclaration, UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets,
     UseEqInstead, WrapType,
 };
+use crate::parser::FnContext;
 use crate::parser::attr::InnerAttrPolicy;
 use crate::{exp, fluent_generated as fluent};
 
@@ -2246,6 +2247,7 @@ impl<'a> Parser<'a> {
         pat: Box<ast::Pat>,
         require_name: bool,
         first_param: bool,
+        fn_parse_mode: &crate::parser::item::FnParseMode,
     ) -> Option<Ident> {
         // If we find a pattern followed by an identifier, it could be an (incorrect)
         // C-style parameter declaration.
@@ -2268,7 +2270,14 @@ impl<'a> Parser<'a> {
                 || self.token == token::Lt
                 || self.token == token::CloseParen)
         {
-            let rfc_note = "anonymous parameters are removed in the 2018 edition (see RFC 1685)";
+            let maybe_emit_anon_params_note = |this: &mut Self, err: &mut Diag<'_>| {
+                let ed = this.token.span.with_neighbor(this.prev_token.span).edition();
+                if matches!(fn_parse_mode.context, crate::parser::item::FnContext::Trait)
+                    && (fn_parse_mode.req_name)(ed)
+                {
+                    err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                }
+            };
 
             let (ident, self_sugg, param_sugg, type_sugg, self_span, param_span, type_span) =
                 match pat.kind {
@@ -2305,15 +2314,21 @@ impl<'a> Parser<'a> {
                                 "_: ".to_string(),
                                 Applicability::MachineApplicable,
                             );
-                            err.note(rfc_note);
+                            maybe_emit_anon_params_note(self, err);
                         }
 
                         return None;
                     }
                 };
 
             // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
-            if first_param {
+            if first_param
+                // Only when the fn is a method, we emit this suggestion.
+                && matches!(
+                    fn_parse_mode.context,
+                    FnContext::Trait | FnContext::Impl
+                )
+            {
                 err.span_suggestion_verbose(
                     self_span,
                     "if this is a `self` type, give it a parameter name",
@@ -2337,7 +2352,7 @@ impl<'a> Parser<'a> {
                 type_sugg,
                 Applicability::MachineApplicable,
             );
-            err.note(rfc_note);
+            maybe_emit_anon_params_note(self, err);
 
             // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
             return if self.token == token::Lt { None } else { Some(ident) };

compiler/rustc_parse/src/parser/item.rs

@@ -116,7 +116,8 @@ impl<'a> Parser<'a> {
 
 impl<'a> Parser<'a> {
     pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<Box<Item>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true };
         self.parse_item_(fn_parse_mode, force_collect).map(|i| i.map(Box::new))
     }
 
@@ -975,16 +976,20 @@ impl<'a> Parser<'a> {
         &mut self,
         force_collect: ForceCollect,
     ) -> PResult<'a, Option<Option<Box<AssocItem>>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Impl, req_body: true };
         self.parse_assoc_item(fn_parse_mode, force_collect)
     }
 
     pub fn parse_trait_item(
         &mut self,
         force_collect: ForceCollect,
     ) -> PResult<'a, Option<Option<Box<AssocItem>>>> {
-        let fn_parse_mode =
-            FnParseMode { req_name: |edition| edition >= Edition::Edition2018, req_body: false };
+        let fn_parse_mode = FnParseMode {
+            req_name: |edition| edition >= Edition::Edition2018,
+            context: FnContext::Trait,
+            req_body: false,
+        };
         self.parse_assoc_item(fn_parse_mode, force_collect)
     }
 
@@ -1261,7 +1266,8 @@ impl<'a> Parser<'a> {
         &mut self,
         force_collect: ForceCollect,
     ) -> PResult<'a, Option<Option<Box<ForeignItem>>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: false };
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: false };
         Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
             |Item { attrs, id, span, vis, kind, tokens }| {
                 let kind = match ForeignItemKind::try_from(kind) {
@@ -2135,7 +2141,8 @@ impl<'a> Parser<'a> {
                 let inherited_vis =
                     Visibility { span: DUMMY_SP, kind: VisibilityKind::Inherited, tokens: None };
                 // We use `parse_fn` to get a span for the function
-                let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+                let fn_parse_mode =
+                    FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true };
                 match self.parse_fn(
                     &mut AttrVec::new(),
                     fn_parse_mode,
@@ -2403,6 +2410,9 @@ pub(crate) struct FnParseMode {
     ///   * The span is from Edition 2015. In particular, you can get a
     ///     2015 span inside a 2021 crate using macros.
     pub(super) req_name: ReqName,
+    /// The context in which this function is parsed, used for diagnostics.
+    /// This indicates the fn is a free function or method and so on.
+    pub(super) context: FnContext,
     /// If this flag is set to `true`, then plain, semicolon-terminated function
     /// prototypes are not allowed here.
     ///
@@ -2424,6 +2434,18 @@ pub(crate) struct FnParseMode {
     pub(super) req_body: bool,
 }
 
+/// The context in which a function is parsed.
+/// FIXME(estebank, xizheyin): Use more variants.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub(crate) enum FnContext {
+    /// Free context.
+    Free,
+    /// A Trait context.
+    Trait,
+    /// An Impl block.
+    Impl,
+}
+
 /// Parsing of functions and methods.
 impl<'a> Parser<'a> {
     /// Parse a function starting from the front matter (`const ...`) to the body `{ ... }` or `;`.
@@ -2439,11 +2461,8 @@ impl<'a> Parser<'a> {
         let header = self.parse_fn_front_matter(vis, case, FrontMatterParsingMode::Function)?; // `const ... fn`
         let ident = self.parse_ident()?; // `foo`
         let mut generics = self.parse_generics()?; // `<'a, T, ...>`
-        let decl = match self.parse_fn_decl(
-            fn_parse_mode.req_name,
-            AllowPlus::Yes,
-            RecoverReturnSign::Yes,
-        ) {
+        let decl = match self.parse_fn_decl(&fn_parse_mode, AllowPlus::Yes, RecoverReturnSign::Yes)
+        {
             Ok(decl) => decl,
             Err(old_err) => {
                 // If we see `for Ty ...` then user probably meant `impl` item.
@@ -2961,18 +2980,21 @@ impl<'a> Parser<'a> {
     /// Parses the parameter list and result type of a function declaration.
     pub(super) fn parse_fn_decl(
         &mut self,
-        req_name: ReqName,
+        fn_parse_mode: &FnParseMode,
         ret_allow_plus: AllowPlus,
         recover_return_sign: RecoverReturnSign,
     ) -> PResult<'a, Box<FnDecl>> {
         Ok(Box::new(FnDecl {
-            inputs: self.parse_fn_params(req_name)?,
+            inputs: self.parse_fn_params(fn_parse_mode)?,
             output: self.parse_ret_ty(ret_allow_plus, RecoverQPath::Yes, recover_return_sign)?,
         }))
     }
 
     /// Parses the parameter list of a function, including the `(` and `)` delimiters.
-    pub(super) fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, ThinVec<Param>> {
+    pub(super) fn parse_fn_params(
+        &mut self,
+        fn_parse_mode: &FnParseMode,
+    ) -> PResult<'a, ThinVec<Param>> {
         let mut first_param = true;
         // Parse the arguments, starting out with `self` being allowed...
         if self.token != TokenKind::OpenParen
@@ -2988,7 +3010,7 @@ impl<'a> Parser<'a> {
         let (mut params, _) = self.parse_paren_comma_seq(|p| {
             p.recover_vcs_conflict_marker();
             let snapshot = p.create_snapshot_for_diagnostic();
-            let param = p.parse_param_general(req_name, first_param, true).or_else(|e| {
+            let param = p.parse_param_general(fn_parse_mode, first_param, true).or_else(|e| {
                 let guar = e.emit();
                 // When parsing a param failed, we should check to make the span of the param
                 // not contain '(' before it.
@@ -3019,7 +3041,7 @@ impl<'a> Parser<'a> {
     /// - `recover_arg_parse` is used to recover from a failed argument parse.
     pub(super) fn parse_param_general(
         &mut self,
-        req_name: ReqName,
+        fn_parse_mode: &FnParseMode,
         first_param: bool,
         recover_arg_parse: bool,
     ) -> PResult<'a, Param> {
@@ -3035,16 +3057,22 @@ impl<'a> Parser<'a> {
 
             let is_name_required = match this.token.kind {
                 token::DotDotDot => false,
-                _ => req_name(this.token.span.with_neighbor(this.prev_token.span).edition()),
+                _ => (fn_parse_mode.req_name)(
+                    this.token.span.with_neighbor(this.prev_token.span).edition(),
+                ),
             };
             let (pat, ty) = if is_name_required || this.is_named_param() {
                 debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
                 let (pat, colon) = this.parse_fn_param_pat_colon()?;
                 if !colon {
                     let mut err = this.unexpected().unwrap_err();
-                    return if let Some(ident) =
-                        this.parameter_without_type(&mut err, pat, is_name_required, first_param)
-                    {
+                    return if let Some(ident) = this.parameter_without_type(
+                        &mut err,
+                        pat,
+                        is_name_required,
+                        first_param,
+                        fn_parse_mode,
+                    ) {
                         let guar = err.emit();
                         Ok((dummy_arg(ident, guar), Trailing::No, UsePreAttrPos::No))
                     } else {

compiler/rustc_parse/src/parser/mod.rs

@@ -22,7 +22,7 @@ use std::{fmt, mem, slice};
 use attr_wrapper::{AttrWrapper, UsePreAttrPos};
 pub use diagnostics::AttemptLocalParseRecovery;
 pub(crate) use expr::ForbiddenLetReason;
-pub(crate) use item::FnParseMode;
+pub(crate) use item::{FnContext, FnParseMode};
 pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 use path::PathStyle;
 use rustc_ast::token::{

compiler/rustc_parse/src/parser/path.rs

@@ -20,7 +20,9 @@ use crate::errors::{
     PathFoundAttributeInParams, PathFoundCVariadicParams, PathSingleColon, PathTripleColon,
 };
 use crate::exp;
-use crate::parser::{CommaRecoveryMode, ExprKind, RecoverColon, RecoverComma};
+use crate::parser::{
+    CommaRecoveryMode, ExprKind, FnContext, FnParseMode, RecoverColon, RecoverComma,
+};
 
 /// Specifies how to parse a path.
 #[derive(Copy, Clone, PartialEq)]
@@ -399,7 +401,13 @@ impl<'a> Parser<'a> {
 
                     let dcx = self.dcx();
                     let parse_params_result = self.parse_paren_comma_seq(|p| {
-                        let param = p.parse_param_general(|_| false, false, false);
+                        // Inside parenthesized type arguments, we want types only, not names.
+                        let mode = FnParseMode {
+                            context: FnContext::Free,
+                            req_name: |_| false,
+                            req_body: false,
+                        };
+                        let param = p.parse_param_general(&mode, false, false);
                         param.map(move |param| {
                             if !matches!(param.pat.kind, PatKind::Missing) {
                                 dcx.emit_err(FnPathFoundNamedParams {

compiler/rustc_parse/src/parser/stmt.rs

@@ -19,8 +19,8 @@ use super::diagnostics::AttemptLocalParseRecovery;
 use super::pat::{PatternLocation, RecoverComma};
 use super::path::PathStyle;
 use super::{
-    AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
-    Trailing, UsePreAttrPos,
+    AttrWrapper, BlockMode, FnContext, FnParseMode, ForceCollect, Parser, Restrictions,
+    SemiColonMode, Trailing, UsePreAttrPos,
 };
 use crate::errors::{self, MalformedLoopLabel};
 use crate::exp;
@@ -153,7 +153,7 @@ impl<'a> Parser<'a> {
             attrs.clone(), // FIXME: unwanted clone of attrs
             false,
             true,
-            FnParseMode { req_name: |_| true, req_body: true },
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true },
             force_collect,
         )? {
             self.mk_stmt(lo.to(item.span), StmtKind::Item(Box::new(item)))

compiler/rustc_parse/src/parser/ty.rs

@@ -19,6 +19,7 @@ use crate::errors::{
     NestedCVariadicType, ReturnTypesUseThinArrow,
 };
 use crate::parser::item::FrontMatterParsingMode;
+use crate::parser::{FnContext, FnParseMode};
 use crate::{exp, maybe_recover_from_interpolated_ty_qpath};
 
 /// Signals whether parsing a type should allow `+`.
@@ -769,7 +770,12 @@ impl<'a> Parser<'a> {
         if self.may_recover() && self.token == TokenKind::Lt {
             self.recover_fn_ptr_with_generics(lo, &mut params, param_insertion_point)?;
         }
-        let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
+        let mode = crate::parser::item::FnParseMode {
+            req_name: |_| false,
+            context: FnContext::Free,
+            req_body: false,
+        };
+        let decl = self.parse_fn_decl(&mode, AllowPlus::No, recover_return_sign)?;
 
         let decl_span = span_start.to(self.prev_token.span);
         Ok(TyKind::FnPtr(Box::new(FnPtrTy {
@@ -1314,7 +1320,8 @@ impl<'a> Parser<'a> {
         self.bump();
         let args_lo = self.token.span;
         let snapshot = self.create_snapshot_for_diagnostic();
-        match self.parse_fn_decl(|_| false, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
+        let mode = FnParseMode { req_name: |_| false, context: FnContext::Free, req_body: false };
+        match self.parse_fn_decl(&mode, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
             Ok(decl) => {
                 self.dcx().emit_err(ExpectedFnPathFoundFnKeyword { fn_token_span });
                 Some(ast::Path {
@@ -1400,8 +1407,9 @@ impl<'a> Parser<'a> {
 
         // Parse `(T, U) -> R`.
         let inputs_lo = self.token.span;
+        let mode = FnParseMode { req_name: |_| false, context: FnContext::Free, req_body: false };
         let inputs: ThinVec<_> =
-            self.parse_fn_params(|_| false)?.into_iter().map(|input| input.ty).collect();
+            self.parse_fn_params(&mode)?.into_iter().map(|input| input.ty).collect();
         let inputs_span = inputs_lo.to(self.prev_token.span);
         let output = self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
         let args = ast::ParenthesizedArgs {

tests/ui/parser/inverted-parameters.rs

@@ -23,7 +23,6 @@ fn pattern((i32, i32) (a, b)) {}
 fn fizz(i32) {}
 //~^ ERROR expected one of `:`, `@`
 //~| HELP if this is a parameter name, give it a type
-//~| HELP if this is a `self` type, give it a parameter name
 //~| HELP if this is a type, explicitly ignore the parameter name
 
 fn missing_colon(quux S) {}

tests/ui/parser/inverted-parameters.stderr

@@ -34,11 +34,6 @@ error: expected one of `:`, `@`, or `|`, found `)`
 LL | fn fizz(i32) {}
    |            ^ expected one of `:`, `@`, or `|`
    |
-   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
-help: if this is a `self` type, give it a parameter name
-   |
-LL | fn fizz(self: i32) {}
-   |         +++++
 help: if this is a parameter name, give it a type
    |
 LL | fn fizz(i32: TypeName) {}
@@ -49,7 +44,7 @@ LL | fn fizz(_: i32) {}
    |         ++
 
 error: expected one of `:`, `@`, or `|`, found `S`
-  --> $DIR/inverted-parameters.rs:29:23
+  --> $DIR/inverted-parameters.rs:28:23
    |
 LL | fn missing_colon(quux S) {}
    |                  -----^

tests/ui/parser/lifetime-in-pattern.stderr

@@ -16,11 +16,6 @@ error: expected one of `:`, `@`, or `|`, found `)`
 LL | fn test(&'a str) {
    |                ^ expected one of `:`, `@`, or `|`
    |
-   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
-help: if this is a `self` type, give it a parameter name
-   |
-LL | fn test(self: &'a str) {
-   |         +++++
 help: if this is a parameter name, give it a type
    |
 LL - fn test(&'a str) {