update dbg! clippy lint

Author: joboet

src/tools/clippy/clippy_lints/src/dbg_macro.rs

@@ -5,7 +5,7 @@ use clippy_utils::macros::{MacroCall, macro_backtrace};
 use clippy_utils::source::snippet_with_applicability;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
-use rustc_hir::{Closure, ClosureKind, CoroutineKind, Expr, ExprKind, LetStmt, LocalSource, Node, Stmt, StmtKind};
+use rustc_hir::{Arm, Closure, ClosureKind, CoroutineKind, Expr, ExprKind, LetStmt, LocalSource, Node, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_session::impl_lint_pass;
 use rustc_span::{Span, SyntaxContext, sym};
@@ -90,33 +90,27 @@ impl LateLintPass<'_> for DbgMacro {
                                     (macro_call.span, String::from("()"))
                                 }
                             },
-                            // dbg!(1)
-                            ExprKind::Match(val, ..) => (
-                                macro_call.span,
-                                snippet_with_applicability(cx, val.span.source_callsite(), "..", &mut applicability)
-                                    .to_string(),
-                            ),
-                            // dbg!(2, 3)
-                            ExprKind::Tup(
-                                [
-                                    Expr {
-                                        kind: ExprKind::Match(first, ..),
-                                        ..
-                                    },
-                                    ..,
-                                    Expr {
-                                        kind: ExprKind::Match(last, ..),
-                                        ..
-                                    },
-                                ],
-                            ) => {
-                                let snippet = snippet_with_applicability(
-                                    cx,
-                                    first.span.source_callsite().to(last.span.source_callsite()),
-                                    "..",
-                                    &mut applicability,
-                                );
-                                (macro_call.span, format!("({snippet})"))
+                            ExprKind::Match(first, arms, _) => {
+                                let vals = collect_vals(first, arms);
+                                let suggestion = match vals.as_slice() {
+                                    // dbg!(1) => 1
+                                    &[val] => {
+                                        snippet_with_applicability(cx, val.span.source_callsite(), "..", &mut applicability)
+                                            .to_string()
+                                    }
+                                    // dbg!(2, 3) => (2, 3)
+                                    &[first, .., last] => {
+                                        let snippet = snippet_with_applicability(
+                                            cx,
+                                            first.span.source_callsite().to(last.span.source_callsite()),
+                                            "..",
+                                            &mut applicability,
+                                        );
+                                        format!("({snippet})")
+                                    }
+                                    _ => unreachable!(),
+                                };
+                                (macro_call.span, suggestion)
                             },
                             _ => unreachable!(),
                         };
@@ -169,3 +163,33 @@ fn is_async_move_desugar<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx
 fn first_dbg_macro_in_expansion(cx: &LateContext<'_>, span: Span) -> Option<MacroCall> {
     macro_backtrace(span).find(|mc| cx.tcx.is_diagnostic_item(sym::dbg_macro, mc.def_id))
 }
+
+/// Extracts all value expressions from the `match`-tree generated by `dbg!`.
+/// 
+/// E.g. from
+/// ```rust, ignore
+/// match 1 {
+///     tmp_1 => match 2 {
+///         tmp_2 => {
+///             /* printing */
+///             (tmp_1, tmp_2)
+///         }
+///     }
+/// }
+/// ```
+/// this extracts `1` and `2`.
+fn collect_vals<'hir>(first: &'hir Expr<'hir>, mut arms: &'hir [Arm<'hir>]) -> Vec<&'hir Expr<'hir>> {
+    let mut vals = vec![first];
+    loop {
+        let [arm] = arms else { unreachable!("dbg! macro expansion only has single-arm matches") };
+
+        match is_async_move_desugar(arm.body).unwrap_or(arm.body).peel_drop_temps().kind {
+            ExprKind::Block(..) => return vals,
+            ExprKind::Match(val, a, _) => {
+                vals.push(val);
+                arms = a;
+            }
+            _ => unreachable!("dbg! macro expansion only results in block or match expressions"),
+        }
+    }
+}