Rollup merge of #68120 - Centril:ban-range-to-dotdotdot, r=oli-obk

Ban `...X` pats, harden tests, and improve diagnostics

Follow up to #67258 (comment) and #67258 (comment).

r? @cramertj @oli-obk

Author: Centril

src/librustc_parse/parser/expr.rs

@@ -1966,7 +1966,7 @@ impl<'a> Parser<'a> {
         limits: RangeLimits,
     ) -> PResult<'a, ExprKind> {
         if end.is_none() && limits == RangeLimits::Closed {
-            self.error_inclusive_range_with_no_end(self.token.span);
+            self.error_inclusive_range_with_no_end(self.prev_span);
             Ok(ExprKind::Err)
         } else {
             Ok(ExprKind::Range(start, end, limits))

src/librustc_parse/parser/pat.rs

@@ -661,14 +661,34 @@ impl<'a> Parser<'a> {
     pub(super) fn error_inclusive_range_with_no_end(&self, span: Span) {
         use rustc_error_codes::E0586;
         struct_span_err!(self.sess.span_diagnostic, span, E0586, "inclusive range with no end")
-            .help("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
+            .span_suggestion_short(
+                span,
+                "use `..` instead",
+                "..".to_string(),
+                Applicability::MachineApplicable,
+            )
+            .note("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
             .emit();
     }
 
-    /// Parse a range-to pattern, e.g. `..X` and `..=X` where `X` remains to be parsed.
-    fn parse_pat_range_to(&mut self, re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
+    /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
+    ///
+    /// The form `...X` is prohibited to reduce confusion with the potential
+    /// expression syntax `...expr` for splatting in expressions.
+    fn parse_pat_range_to(&mut self, mut re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
         let end = self.parse_pat_range_end()?;
         self.sess.gated_spans.gate(sym::half_open_range_patterns, re.span.to(self.prev_span));
+        if let RangeEnd::Included(ref mut syn @ RangeSyntax::DotDotDot) = &mut re.node {
+            *syn = RangeSyntax::DotDotEq;
+            self.struct_span_err(re.span, "range-to patterns with `...` are not allowed")
+                .span_suggestion_short(
+                    re.span,
+                    "use `..=` instead",
+                    "..=".to_string(),
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+        }
         Ok(PatKind::Range(None, Some(end), re))
     }
 

src/test/ui/error-codes/E0586.stderr

@@ -1,10 +1,10 @@
 error[E0586]: inclusive range with no end
-  --> $DIR/E0586.rs:3:22
+  --> $DIR/E0586.rs:3:19
    |
 LL |     let x = &tmp[1..=];
-   |                      ^
+   |                   ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error: aborting due to previous error
 

src/test/ui/half-open-range-patterns/feature-gate-half-open-range-patterns.rs

@@ -8,6 +8,7 @@ fn foo() {
     //~^ ERROR half-open range patterns are unstable
     if let ...5 = 0 {}
     //~^ ERROR half-open range patterns are unstable
+    //~| ERROR range-to patterns with `...` are not allowed
     if let ..5 = 0 {}
     //~^ ERROR half-open range patterns are unstable
     if let 5.. = 0 {}

src/test/ui/half-open-range-patterns/feature-gate-half-open-range-patterns.stderr

@@ -1,18 +1,24 @@
+error: range-to patterns with `...` are not allowed
+  --> $DIR/feature-gate-half-open-range-patterns.rs:9:12
+   |
+LL |     if let ...5 = 0 {}
+   |            ^^^ help: use `..=` instead
+
 error[E0586]: inclusive range with no end
-  --> $DIR/feature-gate-half-open-range-patterns.rs:15:13
+  --> $DIR/feature-gate-half-open-range-patterns.rs:16:13
    |
 LL |     if let 5..= = 0 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0586]: inclusive range with no end
-  --> $DIR/feature-gate-half-open-range-patterns.rs:18:13
+  --> $DIR/feature-gate-half-open-range-patterns.rs:19:13
    |
 LL |     if let 5... = 0 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0658]: half-open range patterns are unstable
   --> $DIR/feature-gate-half-open-range-patterns.rs:7:12
@@ -33,7 +39,7 @@ LL |     if let ...5 = 0 {}
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
 error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:11:12
+  --> $DIR/feature-gate-half-open-range-patterns.rs:12:12
    |
 LL |     if let ..5 = 0 {}
    |            ^^^
@@ -42,7 +48,7 @@ LL |     if let ..5 = 0 {}
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
 error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:13:12
+  --> $DIR/feature-gate-half-open-range-patterns.rs:14:12
    |
 LL |     if let 5.. = 0 {}
    |            ^^^
@@ -51,7 +57,7 @@ LL |     if let 5.. = 0 {}
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
 error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:15:12
+  --> $DIR/feature-gate-half-open-range-patterns.rs:16:12
    |
 LL |     if let 5..= = 0 {}
    |            ^^^^
@@ -60,15 +66,15 @@ LL |     if let 5..= = 0 {}
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
 error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:18:12
+  --> $DIR/feature-gate-half-open-range-patterns.rs:19:12
    |
 LL |     if let 5... = 0 {}
    |            ^^^^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/67264
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
-error: aborting due to 8 previous errors
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0586, E0658.
 For more information about an error, try `rustc --explain E0586`.

src/test/ui/half-open-range-patterns/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs

@@ -0,0 +1,32 @@
+// Test that `...X` range-to patterns are syntactically invalid.
+//
+// See https://github.com/rust-lang/rust/pull/67258#issuecomment-565656155
+// for the reason why. To summarize, we might want to introduce `...expr` as
+// an expression form for splatting (or "untupling") in an expression context.
+// While there is no syntactic ambiguity with `...X` in a pattern context,
+// there's a potential confusion factor here, and we would prefer to keep patterns
+// and expressions in-sync. As such, we do not allow `...X` in patterns either.
+
+#![feature(half_open_range_patterns)]
+
+fn main() {}
+
+#[cfg(FALSE)]
+fn syntax() {
+    match scrutinee {
+        ...X => {} //~ ERROR range-to patterns with `...` are not allowed
+        ...0 => {} //~ ERROR range-to patterns with `...` are not allowed
+        ...'a' => {} //~ ERROR range-to patterns with `...` are not allowed
+        ...0.0f32 => {} //~ ERROR range-to patterns with `...` are not allowed
+    }
+}
+
+fn syntax2() {
+    macro_rules! mac {
+        ($e:expr) => {
+            let ...$e; //~ ERROR range-to patterns with `...` are not allowed
+        }
+    }
+
+    mac!(0);
+}

src/test/ui/half-open-range-patterns/half-open-range-pats-inclusive-dotdotdot-bad-syntax.stderr

@@ -0,0 +1,35 @@
+error: range-to patterns with `...` are not allowed
+  --> $DIR/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs:17:9
+   |
+LL |         ...X => {}
+   |         ^^^ help: use `..=` instead
+
+error: range-to patterns with `...` are not allowed
+  --> $DIR/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs:18:9
+   |
+LL |         ...0 => {}
+   |         ^^^ help: use `..=` instead
+
+error: range-to patterns with `...` are not allowed
+  --> $DIR/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs:19:9
+   |
+LL |         ...'a' => {}
+   |         ^^^ help: use `..=` instead
+
+error: range-to patterns with `...` are not allowed
+  --> $DIR/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs:20:9
+   |
+LL |         ...0.0f32 => {}
+   |         ^^^ help: use `..=` instead
+
+error: range-to patterns with `...` are not allowed
+  --> $DIR/half-open-range-pats-inclusive-dotdotdot-bad-syntax.rs:27:17
+   |
+LL |             let ...$e;
+   |                 ^^^ help: use `..=` instead
+...
+LL |     mac!(0);
+   |     -------- in this macro invocation
+
+error: aborting due to 5 previous errors
+

src/test/ui/half-open-range-patterns/half-open-range-pats-inclusive-no-end.rs

@@ -13,3 +13,14 @@ fn foo() {
     if let X... = 1 {} //~ ERROR inclusive range with no end
     if let X..= = 1 {} //~ ERROR inclusive range with no end
 }
+
+fn bar() {
+    macro_rules! mac {
+        ($e:expr) => {
+            let $e...; //~ ERROR inclusive range with no end
+            let $e..=; //~ ERROR inclusive range with no end
+        }
+    }
+
+    mac!(0);
+}

src/test/ui/half-open-range-patterns/half-open-range-pats-inclusive-no-end.stderr

@@ -2,34 +2,56 @@ error[E0586]: inclusive range with no end
   --> $DIR/half-open-range-pats-inclusive-no-end.rs:10:13
    |
 LL |     if let 0... = 1 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0586]: inclusive range with no end
   --> $DIR/half-open-range-pats-inclusive-no-end.rs:11:13
    |
 LL |     if let 0..= = 1 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0586]: inclusive range with no end
   --> $DIR/half-open-range-pats-inclusive-no-end.rs:13:13
    |
 LL |     if let X... = 1 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0586]: inclusive range with no end
   --> $DIR/half-open-range-pats-inclusive-no-end.rs:14:13
    |
 LL |     if let X..= = 1 {}
-   |             ^^^
+   |             ^^^ help: use `..` instead
    |
-   = help: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: aborting due to 4 previous errors
+error[E0586]: inclusive range with no end
+  --> $DIR/half-open-range-pats-inclusive-no-end.rs:20:19
+   |
+LL |             let $e...;
+   |                   ^^^ help: use `..` instead
+...
+LL |     mac!(0);
+   |     -------- in this macro invocation
+   |
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+
+error[E0586]: inclusive range with no end
+  --> $DIR/half-open-range-pats-inclusive-no-end.rs:21:19
+   |
+LL |             let $e..=;
+   |                   ^^^ help: use `..` instead
+...
+LL |     mac!(0);
+   |     -------- in this macro invocation
+   |
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0586`.

src/test/ui/half-open-range-patterns/half-open-range-pats-ref-ambiguous-interp.rs

@@ -20,5 +20,7 @@ fn syntax() {
         &..=0 | _ => {}
         //~^ ERROR the range pattern here has ambiguous interpretation
         &...0 | _ => {}
+        //~^ ERROR the range pattern here has ambiguous interpretation
+        //~| ERROR range-to patterns with `...` are not allowed
     }
 }