fix: `match_single_binding` wrongly handles scope

5 files changed, 429 insertions, 37 deletions

diff --git a/clippy_lints/src/matches/match_single_binding.rs b/clippy_lints/src/matches/match_single_binding.rs
index 6a76c6cedd0..9790e63821d 100644
--- a/clippy_lints/src/matches/match_single_binding.rs
+++ b/clippy_lints/src/matches/match_single_binding.rs
@@ -1,11 +1,18 @@
+use std::ops::ControlFlow;
+
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::macros::HirNode;
-use clippy_utils::source::{indent_of, snippet, snippet_block_with_context, snippet_with_context};
+use clippy_utils::source::{
+    RelativeIndent, indent_of, reindent_multiline_relative, snippet, snippet_block_with_context, snippet_with_context,
+};
 use clippy_utils::{is_refutable, peel_blocks};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
-use rustc_hir::{Arm, Expr, ExprKind, Node, PatKind, StmtKind};
+use rustc_hir::def::Res;
+use rustc_hir::intravisit::{Visitor, walk_block, walk_expr, walk_path, walk_stmt};
+use rustc_hir::{Arm, Block, Expr, ExprKind, HirId, Node, PatKind, Path, Stmt, StmtKind};
 use rustc_lint::LateContext;
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
 use super::MATCH_SINGLE_BINDING;
 
@@ -50,10 +57,11 @@ pub(crate) fn check<'a>(cx: &LateContext<'a>, ex: &Expr<'a>, arms: &[Arm<'_>], e
                         cx,
                         (ex, expr),
                         (bind_names, matched_vars),
-                        &snippet_body,
+                        snippet_body,
                         &mut app,
                         Some(span),
                         true,
+                        is_var_binding_used_later(cx, expr, &arms[0]),
                     );
 
                     span_lint_and_sugg(
@@ -83,10 +91,11 @@ pub(crate) fn check<'a>(cx: &LateContext<'a>, ex: &Expr<'a>, arms: &[Arm<'_>], e
                         cx,
                         (ex, expr),
                         (bind_names, matched_vars),
-                        &snippet_body,
+                        snippet_body,
                         &mut app,
                         None,
                         true,
+                        is_var_binding_used_later(cx, expr, &arms[0]),
                     );
                     (expr.span, sugg)
                 },
@@ -108,10 +117,11 @@ pub(crate) fn check<'a>(cx: &LateContext<'a>, ex: &Expr<'a>, arms: &[Arm<'_>], e
                     cx,
                     (ex, expr),
                     (bind_names, matched_vars),
-                    &snippet_body,
+                    snippet_body,
                     &mut app,
                     None,
                     false,
+                    true,
                 );
 
                 span_lint_and_sugg(
@@ -139,6 +149,125 @@ pub(crate) fn check<'a>(cx: &LateContext<'a>, ex: &Expr<'a>, arms: &[Arm<'_>], e
     }
 }
 
+struct VarBindingVisitor<'a, 'tcx> {
+    cx: &'a LateContext<'tcx>,
+    identifiers: FxHashSet<Symbol>,
+}
+
+impl<'tcx> Visitor<'tcx> for VarBindingVisitor<'_, 'tcx> {
+    type Result = ControlFlow<()>;
+
+    fn visit_path(&mut self, path: &Path<'tcx>, _: HirId) -> Self::Result {
+        if let Res::Local(_) = path.res
+            && let [segment] = path.segments
+            && self.identifiers.contains(&segment.ident.name)
+        {
+            return ControlFlow::Break(());
+        }
+
+        walk_path(self, path)
+    }
+
+    fn visit_block(&mut self, block: &'tcx Block<'tcx>) -> Self::Result {
+        let before = self.identifiers.clone();
+        walk_block(self, block)?;
+        self.identifiers = before;
+        ControlFlow::Continue(())
+    }
+
+    fn visit_stmt(&mut self, stmt: &'tcx Stmt<'tcx>) -> Self::Result {
+        if let StmtKind::Let(let_stmt) = stmt.kind {
+            if let Some(init) = let_stmt.init {
+                self.visit_expr(init)?;
+            }
+
+            let_stmt.pat.each_binding(|_, _, _, ident| {
+                self.identifiers.remove(&ident.name);
+            });
+        }
+        walk_stmt(self, stmt)
+    }
+
+    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) -> Self::Result {
+        match expr.kind {
+            ExprKind::If(
+                Expr {
+                    kind: ExprKind::Let(let_expr),
+                    ..
+                },
+                then,
+                else_,
+            ) => {
+                self.visit_expr(let_expr.init)?;
+                let before = self.identifiers.clone();
+                let_expr.pat.each_binding(|_, _, _, ident| {
+                    self.identifiers.remove(&ident.name);
+                });
+
+                self.visit_expr(then)?;
+                self.identifiers = before;
+                if let Some(else_) = else_ {
+                    self.visit_expr(else_)?;
+                }
+                ControlFlow::Continue(())
+            },
+            ExprKind::Closure(closure) => {
+                let body = self.cx.tcx.hir_body(closure.body);
+                let before = self.identifiers.clone();
+                for param in body.params {
+                    param.pat.each_binding(|_, _, _, ident| {
+                        self.identifiers.remove(&ident.name);
+                    });
+                }
+                self.visit_expr(body.value)?;
+                self.identifiers = before;
+                ControlFlow::Continue(())
+            },
+            ExprKind::Match(expr, arms, _) => {
+                self.visit_expr(expr)?;
+                for arm in arms {
+                    let before = self.identifiers.clone();
+                    arm.pat.each_binding(|_, _, _, ident| {
+                        self.identifiers.remove(&ident.name);
+                    });
+                    if let Some(guard) = arm.guard {
+                        self.visit_expr(guard)?;
+                    }
+                    self.visit_expr(arm.body)?;
+                    self.identifiers = before;
+                }
+                ControlFlow::Continue(())
+            },
+            _ => walk_expr(self, expr),
+        }
+    }
+}
+
+fn is_var_binding_used_later(cx: &LateContext<'_>, expr: &Expr<'_>, arm: &Arm<'_>) -> bool {
+    let Node::Stmt(stmt) = cx.tcx.parent_hir_node(expr.hir_id) else {
+        return false;
+    };
+    let Node::Block(block) = cx.tcx.parent_hir_node(stmt.hir_id) else {
+        return false;
+    };
+
+    let mut identifiers = FxHashSet::default();
+    arm.pat.each_binding(|_, _, _, ident| {
+        identifiers.insert(ident.name);
+    });
+
+    let mut visitor = VarBindingVisitor { cx, identifiers };
+    block
+        .stmts
+        .iter()
+        .skip_while(|s| s.hir_id != stmt.hir_id)
+        .skip(1)
+        .any(|stmt| matches!(visitor.visit_stmt(stmt), ControlFlow::Break(())))
+        || block
+            .expr
+            .is_some_and(|expr| matches!(visitor.visit_expr(expr), ControlFlow::Break(())))
+}
+
 /// Returns true if the `ex` match expression is in a local (`let`) or assign expression
 fn opt_parent_assign_span<'a>(cx: &LateContext<'a>, ex: &Expr<'a>) -> Option<AssignmentExpr> {
     if let Node::Expr(parent_arm_expr) = cx.tcx.parent_hir_node(ex.hir_id) {
@@ -161,47 +290,58 @@ fn opt_parent_assign_span<'a>(cx: &LateContext<'a>, ex: &Expr<'a>) -> Option<Ass
     None
 }
 
-fn expr_parent_requires_curlies<'a>(cx: &LateContext<'a>, match_expr: &Expr<'a>) -> bool {
+fn expr_in_nested_block(cx: &LateContext<'_>, match_expr: &Expr<'_>) -> bool {
+    if let Node::Block(block) = cx.tcx.parent_hir_node(match_expr.hir_id) {
+        return block
+            .expr
+            .map_or_else(|| matches!(block.stmts, [_]), |_| block.stmts.is_empty());
+    }
+    false
+}
+
+fn expr_must_have_curlies(cx: &LateContext<'_>, match_expr: &Expr<'_>) -> bool {
     let parent = cx.tcx.parent_hir_node(match_expr.hir_id);
-    matches!(
-        parent,
-        Node::Expr(Expr {
-            kind: ExprKind::Closure { .. },
-            ..
-        }) | Node::AnonConst(..)
+    if let Node::Expr(Expr {
+        kind: ExprKind::Closure { .. },
+        ..
+    })
+    | Node::AnonConst(..) = parent
+    {
+        return true;
+    }
+
+    if let Node::Arm(arm) = &cx.tcx.parent_hir_node(match_expr.hir_id)
+        && let ExprKind::Match(..) = arm.body.kind
+    {
+        return true;
+    }
+
+    false
+}
+
+fn reindent_snippet_if_in_block(snippet_body: &str, has_assignment: bool) -> String {
+    if has_assignment || !snippet_body.starts_with('{') {
+        return reindent_multiline_relative(snippet_body, true, RelativeIndent::Add(0));
+    }
+
+    reindent_multiline_relative(
+        snippet_body.trim_start_matches('{').trim_end_matches('}').trim(),
+        false,
+        RelativeIndent::Sub(4),
     )
 }
 
+#[expect(clippy::too_many_arguments)]
 fn sugg_with_curlies<'a>(
     cx: &LateContext<'a>,
     (ex, match_expr): (&Expr<'a>, &Expr<'a>),
     (bind_names, matched_vars): (Span, Span),
-    snippet_body: &str,
+    mut snippet_body: String,
     applicability: &mut Applicability,
     assignment: Option<Span>,
     needs_var_binding: bool,
+    is_var_binding_used_later: bool,
 ) -> String {
-    let mut indent = " ".repeat(indent_of(cx, ex.span).unwrap_or(0));
-
-    let (mut cbrace_start, mut cbrace_end) = (String::new(), String::new());
-    if expr_parent_requires_curlies(cx, match_expr) {
-        cbrace_end = format!("\n{indent}}}");
-        // Fix body indent due to the closure
-        indent = " ".repeat(indent_of(cx, bind_names).unwrap_or(0));
-        cbrace_start = format!("{{\n{indent}");
-    }
-
-    // If the parent is already an arm, and the body is another match statement,
-    // we need curly braces around suggestion
-    if let Node::Arm(arm) = &cx.tcx.parent_hir_node(match_expr.hir_id)
-        && let ExprKind::Match(..) = arm.body.kind
-    {
-        cbrace_end = format!("\n{indent}}}");
-        // Fix body indent due to the match
-        indent = " ".repeat(indent_of(cx, bind_names).unwrap_or(0));
-        cbrace_start = format!("{{\n{indent}");
-    }
-
     let assignment_str = assignment.map_or_else(String::new, |span| {
         let mut s = snippet(cx, span, "..").to_string();
         s.push_str(" = ");
@@ -221,5 +361,17 @@ fn sugg_with_curlies<'a>(
             .to_string()
     };
 
+    let mut indent = " ".repeat(indent_of(cx, ex.span).unwrap_or(0));
+    let (mut cbrace_start, mut cbrace_end) = (String::new(), String::new());
+    if !expr_in_nested_block(cx, match_expr)
+        && ((needs_var_binding && is_var_binding_used_later) || expr_must_have_curlies(cx, match_expr))
+    {
+        cbrace_end = format!("\n{indent}}}");
+        // Fix body indent due to the closure
+        indent = " ".repeat(indent_of(cx, bind_names).unwrap_or(0));
+        cbrace_start = format!("{{\n{indent}");
+        snippet_body = reindent_snippet_if_in_block(&snippet_body, !assignment_str.is_empty());
+    }
+
     format!("{cbrace_start}{scrutinee};\n{indent}{assignment_str}{snippet_body}{cbrace_end}")
 }
diff --git a/clippy_utils/src/source.rs b/clippy_utils/src/source.rs
index 7f2bf99daff..b490902429f 100644
--- a/clippy_utils/src/source.rs
+++ b/clippy_utils/src/source.rs
@@ -18,7 +18,7 @@ use rustc_span::{
 };
 use std::borrow::Cow;
 use std::fmt;
-use std::ops::{Deref, Index, Range};
+use std::ops::{Add, Deref, Index, Range};
 
 pub trait HasSession {
     fn sess(&self) -> &Session;
@@ -476,6 +476,38 @@ pub fn position_before_rarrow(s: &str) -> Option<usize> {
     })
 }
 
+pub enum RelativeIndent {
+    Add(usize),
+    Sub(usize),
+}
+
+impl Add<RelativeIndent> for usize {
+    type Output = usize;
+
+    fn add(self, rhs: RelativeIndent) -> Self::Output {
+        match rhs {
+            RelativeIndent::Add(n) => self + n,
+            RelativeIndent::Sub(n) => self.saturating_sub(n),
+        }
+    }
+}
+
+/// Reindents a multiline string with possibility of ignoring the first line and relative
+/// indentation.
+pub fn reindent_multiline_relative(s: &str, ignore_first: bool, relative_indent: RelativeIndent) -> String {
+    fn indent_of_string(s: &str) -> usize {
+        s.find(|c: char| !c.is_whitespace()).unwrap_or(0)
+    }
+
+    let mut indent = 0;
+    if let Some(line) = s.lines().nth(usize::from(ignore_first)) {
+        let line_indent = indent_of_string(line);
+        indent = line_indent + relative_indent;
+    }
+
+    reindent_multiline(s, ignore_first, Some(indent))
+}
+
 /// Reindent a multiline string with possibility of ignoring the first line.
 pub fn reindent_multiline(s: &str, ignore_first: bool, indent: Option<usize>) -> String {
     let s_space = reindent_multiline_inner(s, ignore_first, indent, ' ');
diff --git a/tests/ui/match_single_binding.fixed b/tests/ui/match_single_binding.fixed
index e11dea35204..d8d865ee44c 100644
--- a/tests/ui/match_single_binding.fixed
+++ b/tests/ui/match_single_binding.fixed
@@ -204,3 +204,56 @@ mod issue14991 {
         }],
     }
 }
+
+mod issue15018 {
+    fn used_later(a: i32, b: i32, c: i32) {
+        let x = 1;
+        {
+            let (x, y, z) = (a, b, c);
+            println!("{} {} {}", x, y, z);
+        }
+        println!("x = {x}");
+    }
+
+    fn not_used_later(a: i32, b: i32, c: i32) {
+        let (x, y, z) = (a, b, c);
+        println!("{} {} {}", x, y, z)
+    }
+
+    #[allow(irrefutable_let_patterns)]
+    fn not_used_later_but_shadowed(a: i32, b: i32, c: i32) {
+        let (x, y, z) = (a, b, c);
+        println!("{} {} {}", x, y, z);
+        let x = 1;
+        println!("x = {x}");
+    }
+
+    #[allow(irrefutable_let_patterns)]
+    fn not_used_later_but_shadowed_nested(a: i32, b: i32, c: i32) {
+        let (x, y, z) = (a, b, c);
+        println!("{} {} {}", x, y, z);
+        if let (x, y, z) = (a, b, c) {
+            println!("{} {} {}", x, y, z)
+        }
+
+        {
+            let x: i32 = 1;
+            {
+                let (x, y, z) = (a, b, c);
+                println!("{} {} {}", x, y, z);
+            }
+            if let (x, y, z) = (a, x, c) {
+                println!("{} {} {}", x, y, z)
+            }
+        }
+
+        {
+            let (x, y, z) = (a, b, c);
+            println!("{} {} {}", x, y, z);
+            let fn_ = |y| {
+                println!("{} {} {}", a, b, y);
+            };
+            fn_(c);
+        }
+    }
+}
diff --git a/tests/ui/match_single_binding.rs b/tests/ui/match_single_binding.rs
index d498da30fc8..ecff945fb91 100644
--- a/tests/ui/match_single_binding.rs
+++ b/tests/ui/match_single_binding.rs
@@ -267,3 +267,64 @@ mod issue14991 {
         }],
     }
 }
+
+mod issue15018 {
+    fn used_later(a: i32, b: i32, c: i32) {
+        let x = 1;
+        match (a, b, c) {
+            //~^ match_single_binding
+            (x, y, z) => println!("{} {} {}", x, y, z),
+        }
+        println!("x = {x}");
+    }
+
+    fn not_used_later(a: i32, b: i32, c: i32) {
+        match (a, b, c) {
+            //~^ match_single_binding
+            (x, y, z) => println!("{} {} {}", x, y, z),
+        }
+    }
+
+    #[allow(irrefutable_let_patterns)]
+    fn not_used_later_but_shadowed(a: i32, b: i32, c: i32) {
+        match (a, b, c) {
+            //~^ match_single_binding
+            (x, y, z) => println!("{} {} {}", x, y, z),
+        }
+        let x = 1;
+        println!("x = {x}");
+    }
+
+    #[allow(irrefutable_let_patterns)]
+    fn not_used_later_but_shadowed_nested(a: i32, b: i32, c: i32) {
+        match (a, b, c) {
+            //~^ match_single_binding
+            (x, y, z) => println!("{} {} {}", x, y, z),
+        }
+        if let (x, y, z) = (a, b, c) {
+            println!("{} {} {}", x, y, z)
+        }
+
+        {
+            let x: i32 = 1;
+            match (a, b, c) {
+                //~^ match_single_binding
+                (x, y, z) => println!("{} {} {}", x, y, z),
+            }
+            if let (x, y, z) = (a, x, c) {
+                println!("{} {} {}", x, y, z)
+            }
+        }
+
+        {
+            match (a, b, c) {
+                //~^ match_single_binding
+                (x, y, z) => println!("{} {} {}", x, y, z),
+            }
+            let fn_ = |y| {
+                println!("{} {} {}", a, b, y);
+            };
+            fn_(c);
+        }
+    }
+}
diff --git a/tests/ui/match_single_binding.stderr b/tests/ui/match_single_binding.stderr
index f274f80c81d..789626de603 100644
--- a/tests/ui/match_single_binding.stderr
+++ b/tests/ui/match_single_binding.stderr
@@ -411,5 +411,99 @@ LL ~             let _n = 1;
 LL +             42
    |
 
-error: aborting due to 29 previous errors
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:274:9
+   |
+LL | /         match (a, b, c) {
+LL | |
+LL | |             (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |         }
+   | |_________^
+   |
+help: consider using a `let` statement
+   |
+LL ~         {
+LL +             let (x, y, z) = (a, b, c);
+LL +             println!("{} {} {}", x, y, z);
+LL +         }
+   |
+
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:282:9
+   |
+LL | /         match (a, b, c) {
+LL | |
+LL | |             (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |         }
+   | |_________^
+   |
+help: consider using a `let` statement
+   |
+LL ~         let (x, y, z) = (a, b, c);
+LL +         println!("{} {} {}", x, y, z)
+   |
+
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:290:9
+   |
+LL | /         match (a, b, c) {
+LL | |
+LL | |             (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |         }
+   | |_________^
+   |
+help: consider using a `let` statement
+   |
+LL ~         let (x, y, z) = (a, b, c);
+LL +         println!("{} {} {}", x, y, z);
+   |
+
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:300:9
+   |
+LL | /         match (a, b, c) {
+LL | |
+LL | |             (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |         }
+   | |_________^
+   |
+help: consider using a `let` statement
+   |
+LL ~         let (x, y, z) = (a, b, c);
+LL +         println!("{} {} {}", x, y, z);
+   |
+
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:310:13
+   |
+LL | /             match (a, b, c) {
+LL | |
+LL | |                 (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |             }
+   | |_____________^
+   |
+help: consider using a `let` statement
+   |
+LL ~             {
+LL +                 let (x, y, z) = (a, b, c);
+LL +                 println!("{} {} {}", x, y, z);
+LL +             }
+   |
+
+error: this match could be written as a `let` statement
+  --> tests/ui/match_single_binding.rs:320:13
+   |
+LL | /             match (a, b, c) {
+LL | |
+LL | |                 (x, y, z) => println!("{} {} {}", x, y, z),
+LL | |             }
+   | |_____________^
+   |
+help: consider using a `let` statement
+   |
+LL ~             let (x, y, z) = (a, b, c);
+LL +             println!("{} {} {}", x, y, z);
+   |
+
+error: aborting due to 35 previous errors