Check for missing space between fat arrow and range pattern

compiler/rustc_error_messages/locales/en-US/parse.ftl

@@ -199,6 +199,17 @@ parse_match_arm_body_without_braces = `match` arm body without braces
         } with a body
     .suggestion_use_comma_not_semicolon = use a comma to end a `match` arm expression
 
+parse_inclusive_range_extra_equals = unexpected `=` after inclusive range
+    .suggestion_remove_eq = use `..=` instead
+    .note = inclusive ranges end with a single equals sign (`..=`)
+
+parse_inclusive_range_match_arrow = unexpected `=>` after open range
+    .suggestion_add_space = add a space between the pattern and `=>`
+
+parse_inclusive_range_no_end = inclusive range with no end
+    .suggestion_open_range = use `..` instead
+    .note = inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+
 parse_struct_literal_not_allowed_here = struct literals are not allowed here
     .suggestion = surround the struct literal with parentheses
 

compiler/rustc_parse/src/errors.rs

@@ -649,6 +649,48 @@ pub(crate) struct MatchArmBodyWithoutBraces {
     pub sub: MatchArmBodyWithoutBracesSugg,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_inclusive_range_extra_equals)]
+#[note]
+pub(crate) struct InclusiveRangeExtraEquals {
+    #[primary_span]
+    #[suggestion(
+        suggestion_remove_eq,
+        style = "short",
+        code = "..=",
+        applicability = "maybe-incorrect"
+    )]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_inclusive_range_match_arrow)]
+pub(crate) struct InclusiveRangeMatchArrow {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(
+        suggestion_add_space,
+        style = "verbose",
+        code = " ",
+        applicability = "machine-applicable"
+    )]
+    pub after_pat: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_inclusive_range_no_end, code = "E0586")]
+#[note]
+pub(crate) struct InclusiveRangeNoEnd {
+    #[primary_span]
+    #[suggestion(
+        suggestion_open_range,
+        code = "..",
+        applicability = "machine-applicable",
+        style = "short"
+    )]
+    pub span: Span,
+}
+
 #[derive(Subdiagnostic)]
 pub(crate) enum MatchArmBodyWithoutBracesSugg {
     #[multipart_suggestion(suggestion_add_braces, applicability = "machine-applicable")]

compiler/rustc_parse/src/parser/expr.rs

@@ -3168,7 +3168,7 @@ impl<'a> Parser<'a> {
         limits: RangeLimits,
     ) -> ExprKind {
         if end.is_none() && limits == RangeLimits::Closed {
-            self.inclusive_range_with_incorrect_end(self.prev_token.span);
+            self.inclusive_range_with_incorrect_end();
             ExprKind::Err
         } else {
             ExprKind::Range(start, end, limits)

compiler/rustc_parse/src/parser/pat.rs

@@ -1,5 +1,7 @@
 use super::{ForceCollect, Parser, PathStyle, TrailingToken};
-use crate::errors::RemoveLet;
+use crate::errors::{
+    InclusiveRangeExtraEquals, InclusiveRangeMatchArrow, InclusiveRangeNoEnd, RemoveLet,
+};
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
 use rustc_ast::ptr::P;
@@ -9,7 +11,7 @@ use rustc_ast::{
     PatField, PatKind, Path, QSelf, RangeEnd, RangeSyntax,
 };
 use rustc_ast_pretty::pprust;
-use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::{respan, Span, Spanned};
 use rustc_span::symbol::{kw, sym, Ident};
@@ -746,47 +748,52 @@ impl<'a> Parser<'a> {
             // Parsing e.g. `X..`.
             if let RangeEnd::Included(_) = re.node {
                 // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
-                self.inclusive_range_with_incorrect_end(re.span);
+                self.inclusive_range_with_incorrect_end();
             }
             None
         };
         Ok(PatKind::Range(Some(begin), end, re))
     }
 
-    pub(super) fn inclusive_range_with_incorrect_end(&mut self, span: Span) {
+    pub(super) fn inclusive_range_with_incorrect_end(&mut self) {
         let tok = &self.token;
-
+        let span = self.prev_token.span;
         // If the user typed "..==" instead of "..=", we want to give them
         // a specific error message telling them to use "..=".
+        // If they typed "..=>", suggest they use ".. =>".
         // Otherwise, we assume that they meant to type a half open exclusive
         // range and give them an error telling them to do that instead.
-        if matches!(tok.kind, token::Eq) && tok.span.lo() == span.hi() {
-            let span_with_eq = span.to(tok.span);
+        let no_space = tok.span.lo() == span.hi();
+        match tok.kind {
+            token::Eq if no_space => {
+                let span_with_eq = span.to(tok.span);
 
-            // Ensure the user doesn't receive unhelpful unexpected token errors
-            self.bump();
-            if self.is_pat_range_end_start(0) {
-                let _ = self.parse_pat_range_end().map_err(|e| e.cancel());
-            }
+                // Ensure the user doesn't receive unhelpful unexpected token errors
+                self.bump();
+                if self.is_pat_range_end_start(0) {
+                    let _ = self.parse_pat_range_end().map_err(|e| e.cancel());
+                }
 
-            self.error_inclusive_range_with_extra_equals(span_with_eq);
-        } else {
-            self.error_inclusive_range_with_no_end(span);
+                self.error_inclusive_range_with_extra_equals(span_with_eq);
+            }
+            token::Gt if no_space => {
+                self.error_inclusive_range_match_arrow(span);
+            }
+            _ => self.error_inclusive_range_with_no_end(span),
         }
     }
 
     fn error_inclusive_range_with_extra_equals(&self, span: Span) {
-        self.struct_span_err(span, "unexpected `=` after inclusive range")
-            .span_suggestion_short(span, "use `..=` instead", "..=", Applicability::MaybeIncorrect)
-            .note("inclusive ranges end with a single equals sign (`..=`)")
-            .emit();
+        self.sess.emit_err(InclusiveRangeExtraEquals { span });
+    }
+
+    fn error_inclusive_range_match_arrow(&self, span: Span) {
+        let after_pat = span.with_hi(span.hi() - rustc_span::BytePos(1)).shrink_to_hi();
+        self.sess.emit_err(InclusiveRangeMatchArrow { span, after_pat });
     }
 
     fn error_inclusive_range_with_no_end(&self, span: Span) {
-        struct_span_err!(self.sess.span_diagnostic, span, E0586, "inclusive range with no end")
-            .span_suggestion_short(span, "use `..` instead", "..", Applicability::MachineApplicable)
-            .note("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
-            .emit();
+        self.sess.emit_err(InclusiveRangeNoEnd { span });
     }
 
     /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.

tests/ui/half-open-range-patterns/half-open-range-pats-inclusive-match-arrow.rs

@@ -0,0 +1,8 @@
+fn main() {
+    let x = 42;
+    match x {
+        0..=73 => {},
+        74..=> {},   //~ ERROR unexpected `=>` after open range
+                     //~^ ERROR expected one of `=>`, `if`, or `|`, found `>`
+    }
+}

tests/ui/half-open-range-patterns/half-open-range-pats-inclusive-match-arrow.stderr

@@ -0,0 +1,19 @@
+error: unexpected `=>` after open range
+  --> $DIR/half-open-range-pats-inclusive-match-arrow.rs:5:11
+   |
+LL |         74..=> {},
+   |           ^^^
+   |
+help: add a space between the pattern and `=>`
+   |
+LL |         74.. => {},
+   |             +
+
+error: expected one of `=>`, `if`, or `|`, found `>`
+  --> $DIR/half-open-range-pats-inclusive-match-arrow.rs:5:14
+   |
+LL |         74..=> {},
+   |              ^ expected one of `=>`, `if`, or `|`
+
+error: aborting due to 2 previous errors
+