Suggest struct pattern when destructuring Range with .. syntax

Author: Delta17920

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -440,6 +440,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
         self.detect_missing_binding_available_from_pattern(&mut err, path, following_seg);
         self.suggest_at_operator_in_slice_pat_with_range(&mut err, path);
+        self.suggest_range_struct_destructuring(&mut err, path, source);
         self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
 
         if let Some((span, label)) = base_error.span_label {
@@ -1383,6 +1384,41 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         }
     }
 
+    fn suggest_range_struct_destructuring(
+        &self,
+        err: &mut Diag<'_>,
+        path: &[Segment],
+        source: PathSource<'_, '_, '_>,
+    ) {
+        // We accept Expr here because range bounds (start..end) are parsed as expressions
+        if !matches!(source, PathSource::Pat | PathSource::TupleStruct(..) | PathSource::Expr(..)) {
+            return;
+        }
+
+        if let Some(pat) = self.diag_metadata.current_pat
+            && let ast::PatKind::Range(Some(start_expr), Some(end_expr), _) = &pat.kind
+            && let (ast::ExprKind::Path(None, start_path), ast::ExprKind::Path(None, end_path)) =
+                (&start_expr.kind, &end_expr.kind)
+            && path.len() == 1
+        {
+            let ident = path[0].ident;
+
+            if (start_path.segments.len() == 1 && start_path.segments[0].ident == ident)
+                || (end_path.segments.len() == 1 && end_path.segments[0].ident == ident)
+            {
+                let start_name = start_path.segments[0].ident;
+                let end_name = end_path.segments[0].ident;
+
+                err.span_suggestion_verbose(
+                    pat.span,
+                    "if you meant to destructure a `Range`, use the struct pattern",
+                    format!("std::ops::Range {{ start: {}, end: {} }}", start_name, end_name),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        }
+    }
+
     fn suggest_swapping_misplaced_self_ty_and_trait(
         &mut self,
         err: &mut Diag<'_>,

tests/ui/resolve/suggest-range-struct-destructuring.rs

@@ -0,0 +1,15 @@
+use std::ops::Range;
+
+fn test_basic_range(r: Range<u32>) {
+    let start..end = r;
+    //~^ ERROR cannot find value `start` in this scope
+    //~| ERROR cannot find value `end` in this scope
+}
+
+fn test_different_names(r: Range<u32>) {
+    let min..max = r;
+    //~^ ERROR cannot find value `min` in this scope
+    //~| ERROR cannot find value `max` in this scope
+}
+
+fn main() {}

tests/ui/resolve/suggest-range-struct-destructuring.stderr

@@ -0,0 +1,66 @@
+error[E0425]: cannot find value `start` in this scope
+  --> $DIR/suggest-range-struct-destructuring.rs:4:9
+   |
+LL |     let start..end = r;
+   |         ^^^^^ not found in this scope
+   |
+help: if you meant to destructure a `Range`, use the struct pattern
+   |
+LL -     let start..end = r;
+LL +     let std::ops::Range { start: start, end: end } = r;
+   |
+
+error[E0425]: cannot find value `end` in this scope
+  --> $DIR/suggest-range-struct-destructuring.rs:4:16
+   |
+LL |     let start..end = r;
+   |                ^^^ not found in this scope
+   |
+help: if you meant to destructure a `Range`, use the struct pattern
+   |
+LL -     let start..end = r;
+LL +     let std::ops::Range { start: start, end: end } = r;
+   |
+
+error[E0425]: cannot find value `min` in this scope
+  --> $DIR/suggest-range-struct-destructuring.rs:10:9
+   |
+LL |     let min..max = r;
+   |         ^^^
+...
+LL | fn main() {}
+   | --------- similarly named function `main` defined here
+   |
+help: if you meant to destructure a `Range`, use the struct pattern
+   |
+LL -     let min..max = r;
+LL +     let std::ops::Range { start: min, end: max } = r;
+   |
+help: a function with a similar name exists
+   |
+LL |     let main..max = r;
+   |          +
+help: consider importing this function
+   |
+LL + use std::cmp::min;
+   |
+
+error[E0425]: cannot find value `max` in this scope
+  --> $DIR/suggest-range-struct-destructuring.rs:10:14
+   |
+LL |     let min..max = r;
+   |              ^^^ not found in this scope
+   |
+help: if you meant to destructure a `Range`, use the struct pattern
+   |
+LL -     let min..max = r;
+LL +     let std::ops::Range { start: min, end: max } = r;
+   |
+help: consider importing this function
+   |
+LL + use std::cmp::max;
+   |
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0425`.