Handle potentially-shadowing bindings in manual_let_else

This commit also adds more test cases, which work fine but were
mentioned in the issue.

Author: notriddle

clippy_lints/src/manual_let_else.rs

@@ -245,17 +245,36 @@ fn replace_in_pattern(
         }
 
         match pat.kind {
-            PatKind::Binding(_ann, _id, binding_name, opt_subpt) => {
-                let Some((pat_to_put, binding_mode)) = ident_map.get(&binding_name.name) else {
-                    break 'a;
-                };
-                let sn_pfx = binding_mode.prefix_str();
-                let (sn_ptp, _) = snippet_with_context(cx, pat_to_put.span, span.ctxt(), "", app);
-                if let Some(subpt) = opt_subpt {
-                    let subpt = replace_in_pattern(cx, span, ident_map, subpt, app, false);
-                    return format!("{sn_pfx}{sn_ptp} @ {subpt}");
+            PatKind::Binding(ann, _id, binding_name, opt_subpt) => {
+                match (ident_map.get(&binding_name.name), opt_subpt) {
+                    (Some((pat_to_put, binding_mode)), opt_subpt) => {
+                        let sn_pfx = binding_mode.prefix_str();
+                        let (sn_ptp, _) = snippet_with_context(cx, pat_to_put.span, span.ctxt(), "", app);
+                        if let Some(subpt) = opt_subpt {
+                            let subpt = replace_in_pattern(cx, span, ident_map, subpt, app, false);
+                            return format!("{sn_pfx}{sn_ptp} @ {subpt}");
+                        }
+                        return format!("{sn_pfx}{sn_ptp}");
+                    },
+                    (None, Some(subpt)) => {
+                        let subpt = replace_in_pattern(cx, span, ident_map, subpt, app, false);
+                        // scanning for a value that matches is not sensitive to order
+                        #[expect(rustc::potential_query_instability)]
+                        if ident_map.values().any(|(other_pat, _)| {
+                            if let PatKind::Binding(_, _, other_name, _) = other_pat.kind {
+                                other_name == binding_name
+                            } else {
+                                false
+                            }
+                        }) {
+                            // this name is shadowed, and, therefore, not usable
+                            return subpt;
+                        }
+                        let binding_pfx = ann.prefix_str();
+                        return format!("{binding_pfx}{binding_name} @ {subpt}");
+                    },
+                    (None, None) => break 'a,
                 }
-                return format!("{sn_pfx}{sn_ptp}");
             },
             PatKind::Or(pats) => {
                 let patterns = pats

tests/ui/manual_let_else_match.fixed

@@ -137,3 +137,48 @@ fn not_fire() {
 fn issue11579() {
     let Some(msg) = Some("hi") else { unreachable!("can't happen") };
 }
+
+#[derive(Clone, Copy)]
+struct Issue9939<T> {
+    avalanche: T,
+}
+
+fn issue9939() {
+    let issue = Some(Issue9939 { avalanche: 1 });
+    let Some(Issue9939 { avalanche: tornado }) = issue else { unreachable!("can't happen") };
+    let issue = Some(Issue9939 { avalanche: true });
+    let Some(Issue9939 { avalanche: acid_rain }) = issue else { unreachable!("can't happen") };
+    assert_eq!(tornado, 1);
+    assert!(acid_rain);
+
+    // without shadowing
+    let _x @ Some(Issue9939 { avalanche: _y }) = issue else { unreachable!("can't happen") };
+
+    // with shadowing
+    let Some(Issue9939 { avalanche: _x }) = issue else { unreachable!("can't happen") };
+}
+
+#[derive(Clone, Copy)]
+struct Issue9939b<T, U> {
+    earthquake: T,
+    hurricane: U,
+}
+
+fn issue9939b() {
+    let issue = Some(Issue9939b {
+        earthquake: true,
+        hurricane: 1,
+    });
+    let issue @ Some(Issue9939b { earthquake: flood, hurricane: drought }) = issue else { unreachable!("can't happen") };
+    assert_eq!(drought, 1);
+    assert!(flood);
+    assert!(issue.is_some());
+
+    // without shadowing
+    let _x @ Some(Issue9939b { earthquake: erosion, hurricane: _y }) = issue else { unreachable!("can't happen") };
+    assert!(erosion);
+
+    // with shadowing
+    let Some(Issue9939b { earthquake: erosion, hurricane: _x }) = issue else { unreachable!("can't happen") };
+    assert!(erosion);
+}

tests/ui/manual_let_else_match.rs

@@ -177,3 +177,76 @@ fn issue11579() {
         _ => unreachable!("can't happen"),
     };
 }
+
+#[derive(Clone, Copy)]
+struct Issue9939<T> {
+    avalanche: T,
+}
+
+fn issue9939() {
+    let issue = Some(Issue9939 { avalanche: 1 });
+    let tornado = match issue {
+        //~^ manual_let_else
+        Some(Issue9939 { avalanche }) => avalanche,
+        _ => unreachable!("can't happen"),
+    };
+    let issue = Some(Issue9939 { avalanche: true });
+    let acid_rain = match issue {
+        //~^ manual_let_else
+        Some(Issue9939 { avalanche: tornado }) => tornado,
+        _ => unreachable!("can't happen"),
+    };
+    assert_eq!(tornado, 1);
+    assert!(acid_rain);
+
+    // without shadowing
+    let _y = match issue {
+        //~^ manual_let_else
+        _x @ Some(Issue9939 { avalanche }) => avalanche,
+        None => unreachable!("can't happen"),
+    };
+
+    // with shadowing
+    let _x = match issue {
+        //~^ manual_let_else
+        _x @ Some(Issue9939 { avalanche }) => avalanche,
+        None => unreachable!("can't happen"),
+    };
+}
+
+#[derive(Clone, Copy)]
+struct Issue9939b<T, U> {
+    earthquake: T,
+    hurricane: U,
+}
+
+fn issue9939b() {
+    let issue = Some(Issue9939b {
+        earthquake: true,
+        hurricane: 1,
+    });
+    let (issue, drought, flood) = match issue {
+        //~^ manual_let_else
+        flood @ Some(Issue9939b { earthquake, hurricane }) => (flood, hurricane, earthquake),
+        None => unreachable!("can't happen"),
+    };
+    assert_eq!(drought, 1);
+    assert!(flood);
+    assert!(issue.is_some());
+
+    // without shadowing
+    let (_y, erosion) = match issue {
+        //~^ manual_let_else
+        _x @ Some(Issue9939b { earthquake, hurricane }) => (hurricane, earthquake),
+        None => unreachable!("can't happen"),
+    };
+    assert!(erosion);
+
+    // with shadowing
+    let (_x, erosion) = match issue {
+        //~^ manual_let_else
+        _x @ Some(Issue9939b { earthquake, hurricane }) => (hurricane, earthquake),
+        None => unreachable!("can't happen"),
+    };
+    assert!(erosion);
+}

tests/ui/manual_let_else_match.stderr

@@ -101,5 +101,75 @@ LL | |         _ => unreachable!("can't happen"),
 LL | |     };
    | |______^ help: consider writing: `let Some(msg) = Some("hi") else { unreachable!("can't happen") };`
 
-error: aborting due to 10 previous errors
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:188:5
+   |
+LL | /     let tornado = match issue {
+LL | |
+LL | |         Some(Issue9939 { avalanche }) => avalanche,
+LL | |         _ => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let Some(Issue9939 { avalanche: tornado }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:194:5
+   |
+LL | /     let acid_rain = match issue {
+LL | |
+LL | |         Some(Issue9939 { avalanche: tornado }) => tornado,
+LL | |         _ => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let Some(Issue9939 { avalanche: acid_rain }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:203:5
+   |
+LL | /     let _y = match issue {
+LL | |
+LL | |         _x @ Some(Issue9939 { avalanche }) => avalanche,
+LL | |         None => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let _x @ Some(Issue9939 { avalanche: _y }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:210:5
+   |
+LL | /     let _x = match issue {
+LL | |
+LL | |         _x @ Some(Issue9939 { avalanche }) => avalanche,
+LL | |         None => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let Some(Issue9939 { avalanche: _x }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:228:5
+   |
+LL | /     let (issue, drought, flood) = match issue {
+LL | |
+LL | |         flood @ Some(Issue9939b { earthquake, hurricane }) => (flood, hurricane, earthquake),
+LL | |         None => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let issue @ Some(Issue9939b { earthquake: flood, hurricane: drought }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:238:5
+   |
+LL | /     let (_y, erosion) = match issue {
+LL | |
+LL | |         _x @ Some(Issue9939b { earthquake, hurricane }) => (hurricane, earthquake),
+LL | |         None => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let _x @ Some(Issue9939b { earthquake: erosion, hurricane: _y }) = issue else { unreachable!("can't happen") };`
+
+error: this could be rewritten as `let...else`
+  --> tests/ui/manual_let_else_match.rs:246:5
+   |
+LL | /     let (_x, erosion) = match issue {
+LL | |
+LL | |         _x @ Some(Issue9939b { earthquake, hurricane }) => (hurricane, earthquake),
+LL | |         None => unreachable!("can't happen"),
+LL | |     };
+   | |______^ help: consider writing: `let Some(Issue9939b { earthquake: erosion, hurricane: _x }) = issue else { unreachable!("can't happen") };`
+
+error: aborting due to 17 previous errors