Auto merge of #116501 - workingjubilee:rollup-fpzov6m, r=workingjubilee

Rollup of 4 pull requests

Successful merges:

 - #116277 (dont call mir.post_mono_checks in codegen)
 - #116400 (Detect missing `=>` after match guard during parsing)
 - #116458 (Properly export function defined in test which uses global_asm!())
 - #116500 (Add tvOS to target_os for register_dtor)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_codegen_cranelift/src/base.rs

@@ -250,17 +250,6 @@ pub(crate) fn verify_func(
 }
 
 fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
-    if let Err(err) =
-        fx.mir.post_mono_checks(fx.tcx, ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
-    {
-        err.emit_err(fx.tcx);
-        fx.bcx.append_block_params_for_function_params(fx.block_map[START_BLOCK]);
-        fx.bcx.switch_to_block(fx.block_map[START_BLOCK]);
-        // compilation should have been aborted
-        fx.bcx.ins().trap(TrapCode::UnreachableCodeReached);
-        return;
-    }
-
     let arg_uninhabited = fx
         .mir
         .args_iter()

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -21,6 +21,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     }
 
     pub fn eval_mir_constant(&self, constant: &mir::ConstOperand<'tcx>) -> mir::ConstValue<'tcx> {
+        // `MirUsedCollector` visited all constants before codegen began, so if we got here there
+        // can be no more constants that fail to evaluate.
         self.monomorphize(constant.const_)
             .eval(self.cx.tcx(), ty::ParamEnv::reveal_all(), Some(constant.span))
             .expect("erroneous constant not captured by required_consts")

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -209,18 +209,11 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         caller_location: None,
     };
 
-    fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
+    // It may seem like we should iterate over `required_consts` to ensure they all successfully
+    // evaluate; however, the `MirUsedCollector` already did that during the collection phase of
+    // monomorphization so we don't have to do it again.
 
-    // Rust post-monomorphization checks; we later rely on them.
-    if let Err(err) =
-        mir.post_mono_checks(cx.tcx(), ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
-    {
-        err.emit_err(cx.tcx());
-        // This IR shouldn't ever be emitted, but let's try to guard against any of this code
-        // ever running.
-        start_bx.abort();
-        return;
-    }
+    fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
 
     let memory_locals = analyze::non_ssa_locals(&fx);
 

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -750,12 +750,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         // Make sure all the constants required by this frame evaluate successfully (post-monomorphization check).
         if M::POST_MONO_CHECKS {
-            // `ctfe_query` does some error message decoration that we want to be in effect here.
-            self.ctfe_query(None, |tcx| {
-                body.post_mono_checks(*tcx, self.param_env, |c| {
-                    self.subst_from_current_frame_and_normalize_erasing_regions(c)
-                })
-            })?;
+            for &const_ in &body.required_consts {
+                let c =
+                    self.subst_from_current_frame_and_normalize_erasing_regions(const_.const_)?;
+                c.eval(*self.tcx, self.param_env, Some(const_.span)).map_err(|err| {
+                    err.emit_note(*self.tcx);
+                    err
+                })?;
+            }
         }
 
         // done
@@ -1054,14 +1056,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
-    /// Call a query that can return `ErrorHandled`. If `span` is `Some`, point to that span when an error occurs.
+    /// Call a query that can return `ErrorHandled`. Should be used for statics and other globals.
+    /// (`mir::Const`/`ty::Const` have `eval` methods that can be used directly instead.)
     pub fn ctfe_query<T>(
         &self,
-        span: Option<Span>,
         query: impl FnOnce(TyCtxtAt<'tcx>) -> Result<T, ErrorHandled>,
     ) -> Result<T, ErrorHandled> {
         // Use a precise span for better cycle errors.
-        query(self.tcx.at(span.unwrap_or_else(|| self.cur_span()))).map_err(|err| {
+        query(self.tcx.at(self.cur_span())).map_err(|err| {
             err.emit_note(*self.tcx);
             err
         })
@@ -1082,7 +1084,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         } else {
             self.param_env
         };
-        let val = self.ctfe_query(None, |tcx| tcx.eval_to_allocation_raw(param_env.and(gid)))?;
+        let val = self.ctfe_query(|tcx| tcx.eval_to_allocation_raw(param_env.and(gid)))?;
         self.raw_const_to_mplace(val)
     }
 
@@ -1092,7 +1094,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         span: Option<Span>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
-        let const_val = self.ctfe_query(span, |tcx| val.eval(*tcx, self.param_env, span))?;
+        let const_val = val.eval(*self.tcx, self.param_env, span).map_err(|err| {
+            // FIXME: somehow this is reachable even when POST_MONO_CHECKS is on.
+            // Are we not always populating `required_consts`?
+            err.emit_note(*self.tcx);
+            err
+        })?;
         self.const_val_to_op(const_val, val.ty(), layout)
     }
 

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -164,7 +164,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     sym::type_name => Ty::new_static_str(self.tcx.tcx),
                     _ => bug!(),
                 };
-                let val = self.ctfe_query(None, |tcx| {
+                let val = self.ctfe_query(|tcx| {
                     tcx.const_eval_global_id(self.param_env, gid, Some(tcx.span))
                 })?;
                 let val = self.const_val_to_op(val, ty, Some(dest.layout))?;

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -536,7 +536,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
 
                 // We don't give a span -- statics don't need that, they cannot be generic or associated.
-                let val = self.ctfe_query(None, |tcx| tcx.eval_static_initializer(def_id))?;
+                let val = self.ctfe_query(|tcx| tcx.eval_static_initializer(def_id))?;
                 (val, Some(def_id))
             }
         };

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -43,21 +43,6 @@ impl ErrorHandled {
         }
     }
 
-    pub fn emit_err(&self, tcx: TyCtxt<'_>) -> ErrorGuaranteed {
-        match self {
-            &ErrorHandled::Reported(err, span) => {
-                if !err.is_tainted_by_errors && !span.is_dummy() {
-                    tcx.sess.emit_err(error::ErroneousConstant { span });
-                }
-                err.error
-            }
-            &ErrorHandled::TooGeneric(span) => tcx.sess.delay_span_bug(
-                span,
-                "encountered TooGeneric error when monomorphic data was expected",
-            ),
-        }
-    }
-
     pub fn emit_note(&self, tcx: TyCtxt<'_>) {
         match self {
             &ErrorHandled::Reported(err, span) => {

compiler/rustc_middle/src/mir/mod.rs

@@ -2,7 +2,7 @@
 //!
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/mir/index.html
 
-use crate::mir::interpret::{AllocRange, ConstAllocation, ErrorHandled, Scalar};
+use crate::mir::interpret::{AllocRange, ConstAllocation, Scalar};
 use crate::mir::visit::MirVisitable;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable};
@@ -568,34 +568,6 @@ impl<'tcx> Body<'tcx> {
     pub fn is_custom_mir(&self) -> bool {
         self.injection_phase.is_some()
     }
-
-    /// *Must* be called once the full substitution for this body is known, to ensure that the body
-    /// is indeed fit for code generation or consumption more generally.
-    ///
-    /// Sadly there's no nice way to represent an "arbitrary normalizer", so we take one for
-    /// constants specifically. (`Option<GenericArgsRef>` could be used for that, but the fact
-    /// that `Instance::args_for_mir_body` is private and instead instance exposes normalization
-    /// functions makes it seem like exposing the generic args is not the intended strategy.)
-    ///
-    /// Also sadly, CTFE doesn't even know whether it runs on MIR that is already polymorphic or still monomorphic,
-    /// so we cannot just immediately ICE on TooGeneric.
-    ///
-    /// Returns Ok(()) if everything went fine, and `Err` if a problem occurred and got reported.
-    pub fn post_mono_checks(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        normalize_const: impl Fn(Const<'tcx>) -> Result<Const<'tcx>, ErrorHandled>,
-    ) -> Result<(), ErrorHandled> {
-        // For now, the only thing we have to check is is to ensure that all the constants used in
-        // the body successfully evaluate.
-        for &const_ in &self.required_consts {
-            let c = normalize_const(const_.const_)?;
-            c.eval(tcx, param_env, Some(const_.span))?;
-        }
-
-        Ok(())
-    }
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TyEncodable, TyDecodable, HashStable)]

compiler/rustc_middle/src/mir/visit.rs

@@ -184,6 +184,8 @@ macro_rules! make_mir_visitor {
 
             visit_place_fns!($($mutability)?);
 
+            /// This is called for every constant in the MIR body and every `required_consts`
+            /// (i.e., including consts that have been dead-code-eliminated).
             fn visit_constant(
                 &mut self,
                 constant: & $($mutability)? ConstOperand<'tcx>,

compiler/rustc_monomorphize/src/collector.rs

@@ -1426,6 +1426,8 @@ fn collect_used_items<'tcx>(
         );
     }
 
+    // Here we rely on the visitor also visiting `required_consts`, so that we evaluate them
+    // and abort compilation if any of them errors.
     MirUsedCollector {
         tcx,
         body: &body,

compiler/rustc_parse/messages.ftl

@@ -225,6 +225,10 @@ parse_expected_semi_found_str = expected `;`, found `{$token}`
 
 parse_expected_statement_after_outer_attr = expected statement after outer attribute
 
+parse_expected_struct_field = expected one of `,`, `:`, or `{"}"}`, found `{$token}`
+    .label = expected one of `,`, `:`, or `{"}"}`
+    .ident_label = while parsing this struct field
+
 parse_expected_trait_in_trait_impl_found_type = expected a trait, found type
 
 parse_extern_crate_name_with_dashes = crate name using dashes are not valid in `extern crate` statements

compiler/rustc_parse/src/errors.rs

@@ -430,6 +430,17 @@ pub(crate) struct ExpectedElseBlock {
     pub condition_start: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_expected_struct_field)]
+pub(crate) struct ExpectedStructField {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub token: Token,
+    #[label(parse_ident_label)]
+    pub ident_span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_outer_attribute_not_allowed_on_if_else)]
 pub(crate) struct OuterAttributeNotAllowedOnIfElse {

compiler/rustc_parse/src/parser/expr.rs

@@ -2834,7 +2834,7 @@ impl<'a> Parser<'a> {
             )?;
             let guard = if this.eat_keyword(kw::If) {
                 let if_span = this.prev_token.span;
-                let mut cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
+                let mut cond = this.parse_match_guard_condition()?;
 
                 CondChecker { parser: this, forbid_let_reason: None }.visit_expr(&mut cond);
 
@@ -2860,9 +2860,9 @@ impl<'a> Parser<'a> {
                 {
                     err.span_suggestion(
                         this.token.span,
-                        "try using a fat arrow here",
+                        "use a fat arrow to start a match arm",
                         "=>",
-                        Applicability::MaybeIncorrect,
+                        Applicability::MachineApplicable,
                     );
                     err.emit();
                     this.bump();
@@ -2979,6 +2979,33 @@ impl<'a> Parser<'a> {
         })
     }
 
+    fn parse_match_guard_condition(&mut self) -> PResult<'a, P<Expr>> {
+        self.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, None).map_err(
+            |mut err| {
+                if self.prev_token == token::OpenDelim(Delimiter::Brace) {
+                    let sugg_sp = self.prev_token.span.shrink_to_lo();
+                    // Consume everything within the braces, let's avoid further parse
+                    // errors.
+                    self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
+                    let msg = "you might have meant to start a match arm after the match guard";
+                    if self.eat(&token::CloseDelim(Delimiter::Brace)) {
+                        let applicability = if self.token.kind != token::FatArrow {
+                            // We have high confidence that we indeed didn't have a struct
+                            // literal in the match guard, but rather we had some operation
+                            // that ended in a path, immediately followed by a block that was
+                            // meant to be the match arm.
+                            Applicability::MachineApplicable
+                        } else {
+                            Applicability::MaybeIncorrect
+                        };
+                        err.span_suggestion_verbose(sugg_sp, msg, "=> ".to_string(), applicability);
+                    }
+                }
+                err
+            },
+        )
+    }
+
     pub(crate) fn is_builtin(&self) -> bool {
         self.token.is_keyword(kw::Builtin) && self.look_ahead(1, |t| *t == token::Pound)
     }
@@ -3049,9 +3076,10 @@ impl<'a> Parser<'a> {
                     || self.look_ahead(2, |t| t == &token::Colon)
                         && (
                             // `{ ident: token, ` cannot start a block.
-                            self.look_ahead(4, |t| t == &token::Comma) ||
-                // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
-                self.look_ahead(3, |t| !t.can_begin_type())
+                            self.look_ahead(4, |t| t == &token::Comma)
+                                // `{ ident: ` cannot start a block unless it's a type ascription
+                                // `ident: Type`.
+                                || self.look_ahead(3, |t| !t.can_begin_type())
                         )
             )
     }
@@ -3091,6 +3119,7 @@ impl<'a> Parser<'a> {
         let mut fields = ThinVec::new();
         let mut base = ast::StructRest::None;
         let mut recover_async = false;
+        let in_if_guard = self.restrictions.contains(Restrictions::IN_IF_GUARD);
 
         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
             recover_async = true;
@@ -3128,6 +3157,26 @@ impl<'a> Parser<'a> {
                         e.span_label(pth.span, "while parsing this struct");
                     }
 
+                    if let Some((ident, _)) = self.token.ident()
+                        && !self.token.is_reserved_ident()
+                        && self.look_ahead(1, |t| {
+                            AssocOp::from_token(&t).is_some()
+                                || matches!(t.kind, token::OpenDelim(_))
+                                || t.kind == token::Dot
+                        })
+                    {
+                        // Looks like they tried to write a shorthand, complex expression.
+                        e.span_suggestion_verbose(
+                            self.token.span.shrink_to_lo(),
+                            "try naming a field",
+                            &format!("{ident}: ", ),
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    if in_if_guard && close_delim == Delimiter::Brace {
+                        return Err(e);
+                    }
+
                     if !recover {
                         return Err(e);
                     }
@@ -3173,19 +3222,6 @@ impl<'a> Parser<'a> {
                                 ",",
                                 Applicability::MachineApplicable,
                             );
-                        } else if is_shorthand
-                            && (AssocOp::from_token(&self.token).is_some()
-                                || matches!(&self.token.kind, token::OpenDelim(_))
-                                || self.token.kind == token::Dot)
-                        {
-                            // Looks like they tried to write a shorthand, complex expression.
-                            let ident = parsed_field.expect("is_shorthand implies Some").ident;
-                            e.span_suggestion(
-                                ident.span.shrink_to_lo(),
-                                "try naming a field",
-                                &format!("{ident}: "),
-                                Applicability::HasPlaceholders,
-                            );
                         }
                     }
                     if !recover {
@@ -3288,6 +3324,24 @@ impl<'a> Parser<'a> {
 
             // Check if a colon exists one ahead. This means we're parsing a fieldname.
             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
+            // Proactively check whether parsing the field will be incorrect.
+            let is_wrong = this.token.is_ident()
+                && !this.token.is_reserved_ident()
+                && !this.look_ahead(1, |t| {
+                    t == &token::Colon
+                        || t == &token::Eq
+                        || t == &token::Comma
+                        || t == &token::CloseDelim(Delimiter::Brace)
+                        || t == &token::CloseDelim(Delimiter::Parenthesis)
+                });
+            if is_wrong {
+                return Err(errors::ExpectedStructField {
+                    span: this.look_ahead(1, |t| t.span),
+                    ident_span: this.token.span,
+                    token: this.look_ahead(1, |t| t.clone()),
+                }
+                .into_diagnostic(&self.sess.span_diagnostic));
+            }
             let (ident, expr) = if is_shorthand {
                 // Mimic `x: x` for the `x` field shorthand.
                 let ident = this.parse_ident_common(false)?;

compiler/rustc_parse/src/parser/mod.rs

@@ -52,6 +52,7 @@ bitflags::bitflags! {
         const NO_STRUCT_LITERAL = 1 << 1;
         const CONST_EXPR        = 1 << 2;
         const ALLOW_LET         = 1 << 3;
+        const IN_IF_GUARD       = 1 << 4;
     }
 }
 

library/std/src/sys/unix/thread_local_dtor.rs

@@ -67,7 +67,7 @@ pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
 // workaround below is to register, via _tlv_atexit, a custom DTOR list once per
 // thread. thread_local dtors are pushed to the DTOR list without calling
 // _tlv_atexit.
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos"))]
+#[cfg(any(target_os = "macos", target_os = "ios", target_os = "watchos", target_os = "tvos"))]
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::cell::Cell;
     use crate::mem;

src/tools/miri/src/concurrency/thread.rs

@@ -803,8 +803,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             if tcx.is_foreign_item(def_id) {
                 throw_unsup_format!("foreign thread-local statics are not supported");
             }
-            // We don't give a span -- statics don't need that, they cannot be generic or associated.
-            let allocation = this.ctfe_query(None, |tcx| tcx.eval_static_initializer(def_id))?;
+            let allocation = this.ctfe_query(|tcx| tcx.eval_static_initializer(def_id))?;
             let mut allocation = allocation.inner().clone();
             // This allocation will be deallocated when the thread dies, so it is not in read-only memory.
             allocation.mutability = Mutability::Mut;

tests/ui/asm/x86_64/issue-96797.rs

@@ -11,7 +11,14 @@ use std::arch::global_asm;
 #[no_mangle]
 fn my_func() {}
 
-global_asm!("call_foobar: jmp {}", sym foobar);
+global_asm!("
+.globl call_foobar
+.type call_foobar,@function
+.pushsection .text.call_foobar,\"ax\",@progbits
+call_foobar: jmp {}
+.size call_foobar, .-call_foobar
+.popsection
+", sym foobar);
 
 fn foobar() {}
 

tests/ui/parser/issues/issue-15980.rs

@@ -9,9 +9,6 @@ fn main(){
             //~^ ERROR expected identifier, found keyword `return`
             //~| NOTE expected identifier, found keyword
         }
-        //~^ NOTE expected one of `.`, `=>`, `?`, or an operator
         _ => {}
-        //~^ ERROR expected one of `.`, `=>`, `?`, or an operator, found reserved identifier `_`
-        //~| NOTE unexpected token
     }
 }

tests/ui/parser/issues/issue-15980.stderr

@@ -11,15 +11,10 @@ help: escape `return` to use it as an identifier
    |
 LL |             r#return
    |             ++
-
-error: expected one of `.`, `=>`, `?`, or an operator, found reserved identifier `_`
-  --> $DIR/issue-15980.rs:13:9
+help: you might have meant to start a match arm after the match guard
    |
-LL |         }
-   |          - expected one of `.`, `=>`, `?`, or an operator
-LL |
-LL |         _ => {}
-   |         ^ unexpected token
+LL |         Err(ref e) if e.kind == io::EndOfFile => {
+   |                                               ++
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 

tests/ui/parser/issues/issue-52496.stderr

@@ -8,10 +8,15 @@ error: expected one of `,`, `:`, or `}`, found `.`
   --> $DIR/issue-52496.rs:8:22
    |
 LL |     let _ = Foo { bar.into(), bat: -1, . };
-   |             ---   -  ^ expected one of `,`, `:`, or `}`
+   |             ---   ---^ expected one of `,`, `:`, or `}`
    |             |     |
-   |             |     help: try naming a field: `bar:`
+   |             |     while parsing this struct field
    |             while parsing this struct
+   |
+help: try naming a field
+   |
+LL |     let _ = Foo { bar: bar.into(), bat: -1, . };
+   |                   ++++
 
 error: expected identifier, found `.`
   --> $DIR/issue-52496.rs:8:40

tests/ui/parser/issues/issue-89396.fixed

@@ -8,9 +8,9 @@ fn main() {
     let _ = match opt {
         Some(_) => true,
         //~^ ERROR: expected one of
-        //~| HELP: try using a fat arrow here
+        //~| HELP: use a fat arrow to start a match arm
         None => false,
         //~^ ERROR: expected one of
-        //~| HELP: try using a fat arrow here
+        //~| HELP: use a fat arrow to start a match arm
     };
 }

tests/ui/parser/issues/issue-89396.rs

@@ -8,9 +8,9 @@ fn main() {
     let _ = match opt {
         Some(_) = true,
         //~^ ERROR: expected one of
-        //~| HELP: try using a fat arrow here
+        //~| HELP: use a fat arrow to start a match arm
         None -> false,
         //~^ ERROR: expected one of
-        //~| HELP: try using a fat arrow here
+        //~| HELP: use a fat arrow to start a match arm
     };
 }

tests/ui/parser/issues/issue-89396.stderr

@@ -5,7 +5,7 @@ LL |         Some(_) = true,
    |                 ^
    |                 |
    |                 expected one of `=>`, `if`, or `|`
-   |                 help: try using a fat arrow here: `=>`
+   |                 help: use a fat arrow to start a match arm: `=>`
 
 error: expected one of `=>`, `@`, `if`, or `|`, found `->`
   --> $DIR/issue-89396.rs:12:14
@@ -14,7 +14,7 @@ LL |         None -> false,
    |              ^^
    |              |
    |              expected one of `=>`, `@`, `if`, or `|`
-   |              help: try using a fat arrow here: `=>`
+   |              help: use a fat arrow to start a match arm: `=>`
 
 error: aborting due to 2 previous errors
 

tests/ui/parser/missing-fat-arrow.rs

@@ -0,0 +1,38 @@
+fn main() {
+    let x = 1;
+    let y = 2;
+    let value = 3;
+
+    match value {
+        Some(x) if x == y {
+            self.next_token()?; //~ ERROR expected identifier, found keyword `self`
+        },
+        _ => {}
+    }
+    let _: i32 = (); //~ ERROR mismatched types
+}
+
+struct Foo {
+    value: usize
+}
+
+fn foo(a: Option<&mut Foo>, b: usize) {
+    match a {
+        Some(a) if a.value == b {
+            a.value = 1; //~ ERROR expected one of `,`, `:`, or `}`, found `.`
+        },
+        _ => {}
+    }
+    let _: i32 = (); //~ ERROR mismatched types
+}
+
+fn bar(a: Option<&mut Foo>, b: usize) {
+    match a {
+        Some(a) if a.value == b {
+            a.value, //~ ERROR expected one of `,`, `:`, or `}`, found `.`
+        } => {
+        }
+        _ => {}
+    }
+    let _: i32 = (); //~ ERROR mismatched types
+}

tests/ui/parser/missing-fat-arrow.stderr

@@ -0,0 +1,78 @@
+error: expected identifier, found keyword `self`
+  --> $DIR/missing-fat-arrow.rs:8:13
+   |
+LL |         Some(x) if x == y {
+   |                         - while parsing this struct
+LL |             self.next_token()?;
+   |             ^^^^ expected identifier, found keyword
+   |
+help: you might have meant to start a match arm after the match guard
+   |
+LL |         Some(x) if x == y => {
+   |                           ++
+
+error: expected one of `,`, `:`, or `}`, found `.`
+  --> $DIR/missing-fat-arrow.rs:22:14
+   |
+LL |         Some(a) if a.value == b {
+   |                               - while parsing this struct
+LL |             a.value = 1;
+   |             -^ expected one of `,`, `:`, or `}`
+   |             |
+   |             while parsing this struct field
+   |
+help: try naming a field
+   |
+LL |             a: a.value = 1;
+   |             ++
+help: you might have meant to start a match arm after the match guard
+   |
+LL |         Some(a) if a.value == b => {
+   |                                 ++
+
+error: expected one of `,`, `:`, or `}`, found `.`
+  --> $DIR/missing-fat-arrow.rs:32:14
+   |
+LL |         Some(a) if a.value == b {
+   |                               - while parsing this struct
+LL |             a.value,
+   |             -^ expected one of `,`, `:`, or `}`
+   |             |
+   |             while parsing this struct field
+   |
+help: try naming a field
+   |
+LL |             a: a.value,
+   |             ++
+help: you might have meant to start a match arm after the match guard
+   |
+LL |         Some(a) if a.value == b => {
+   |                                 ++
+
+error[E0308]: mismatched types
+  --> $DIR/missing-fat-arrow.rs:12:18
+   |
+LL |     let _: i32 = ();
+   |            ---   ^^ expected `i32`, found `()`
+   |            |
+   |            expected due to this
+
+error[E0308]: mismatched types
+  --> $DIR/missing-fat-arrow.rs:26:18
+   |
+LL |     let _: i32 = ();
+   |            ---   ^^ expected `i32`, found `()`
+   |            |
+   |            expected due to this
+
+error[E0308]: mismatched types
+  --> $DIR/missing-fat-arrow.rs:37:18
+   |
+LL |     let _: i32 = ();
+   |            ---   ^^ expected `i32`, found `()`
+   |            |
+   |            expected due to this
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/parser/removed-syntax-with-2.stderr

@@ -2,8 +2,9 @@ error: expected one of `,`, `:`, or `}`, found `a`
   --> $DIR/removed-syntax-with-2.rs:8:31
    |
 LL |     let b = S { foo: (), with a };
-   |             -                 ^ expected one of `,`, `:`, or `}`
-   |             |
+   |             -            ---- ^ expected one of `,`, `:`, or `}`
+   |             |            |
+   |             |            while parsing this struct field
    |             while parsing this struct
 
 error[E0063]: missing field `bar` in initializer of `S`