Rollup merge of #154074 - dianne:dbg-temp-scopes, r=Mark-Simulacrum

don't drop arguments' temporaries in `dbg!`

Fixes rust-lang/rust#153850

Credit to @theemathas for help with macro engineering ^^

r? libs

Author: JonathanBrouwer

clippy_lints/src/dbg_macro.rs

@@ -5,7 +5,7 @@ use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::{is_in_test, sym};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
-use rustc_hir::{Arm, Closure, ClosureKind, CoroutineKind, Expr, ExprKind, LetStmt, LocalSource, Node, Stmt, StmtKind};
+use rustc_hir::{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};
@@ -92,16 +92,15 @@ impl LateLintPass<'_> for DbgMacro {
                                 (macro_call.span, String::from("()"))
                             }
                         },
-                        ExprKind::Match(first, arms, _) => {
-                            let vals = collect_vals(first, arms);
-                            let suggestion = match *vals.as_slice() {
+                        ExprKind::Match(args, _, _) => {
+                            let suggestion = match args.kind {
                                 // dbg!(1) => 1
-                                [val] => {
+                                ExprKind::Tup([val]) => {
                                     snippet_with_applicability(cx, val.span.source_callsite(), "..", &mut applicability)
                                         .to_string()
                                 },
                                 // dbg!(2, 3) => (2, 3)
-                                [first, .., last] => {
+                                ExprKind::Tup([first, .., last]) => {
                                     let snippet = snippet_with_applicability(
                                         cx,
                                         first.span.source_callsite().to(last.span.source_callsite()),
@@ -165,39 +164,3 @@ 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"),
-        }
-    }
-}

clippy_utils/src/sym.rs

@@ -200,7 +200,6 @@ generate! {
     cx,
     cycle,
     cyclomatic_complexity,
-    dbg_macro,
     de,
     debug_struct,
     deprecated_in_future,