Auto merge of rust-lang#90485 - camsteffen:fmt-args-less-bind, r=m-ou-se

Don't destructure args tuple in format_args!

This allows Clippy to parse the HIR more simply since `arg0` is changed to `_args.0`. (cc rust-lang/rust-clippy#7843). From rustc's perspective, I think this is something between a lateral move and a tiny improvement since there are fewer bindings.

r? `@m-ou-se`

compiler/rustc_builtin_macros/src/format.rs

@@ -760,16 +760,11 @@ impl<'a, 'b> Context<'a, 'b> {
     /// Actually builds the expression which the format_args! block will be
     /// expanded to.
     fn into_expr(self) -> P<ast::Expr> {
-        let mut locals =
-            Vec::with_capacity((0..self.args.len()).map(|i| self.arg_unique_types[i].len()).sum());
-        let mut counts = Vec::with_capacity(self.count_args.len());
-        let mut pats = Vec::with_capacity(self.args.len());
+        let mut args = Vec::with_capacity(
+            self.arg_unique_types.iter().map(|v| v.len()).sum::<usize>() + self.count_args.len(),
+        );
         let mut heads = Vec::with_capacity(self.args.len());
 
-        let names_pos: Vec<_> = (0..self.args.len())
-            .map(|i| Ident::from_str_and_span(&format!("arg{}", i), self.macsp))
-            .collect();
-
         // First, build up the static array which will become our precompiled
         // format "string"
         let pieces = self.ecx.expr_vec_slice(self.fmtsp, self.str_pieces);
@@ -787,11 +782,8 @@ impl<'a, 'b> Context<'a, 'b> {
         // of each variable because we don't want to move out of the arguments
         // passed to this function.
         for (i, e) in self.args.into_iter().enumerate() {
-            let name = names_pos[i];
-            let span = self.ecx.with_def_site_ctxt(e.span);
-            pats.push(self.ecx.pat_ident(span, name));
             for arg_ty in self.arg_unique_types[i].iter() {
-                locals.push(Context::format_arg(self.ecx, self.macsp, e.span, arg_ty, name));
+                args.push(Context::format_arg(self.ecx, self.macsp, e.span, arg_ty, i));
             }
             heads.push(self.ecx.expr_addr_of(e.span, e));
         }
@@ -800,15 +792,11 @@ impl<'a, 'b> Context<'a, 'b> {
                 Exact(i) => i,
                 _ => panic!("should never happen"),
             };
-            let name = names_pos[index];
             let span = spans_pos[index];
-            counts.push(Context::format_arg(self.ecx, self.macsp, span, &Count, name));
+            args.push(Context::format_arg(self.ecx, self.macsp, span, &Count, index));
         }
 
-        // Now create a vector containing all the arguments
-        let args = locals.into_iter().chain(counts.into_iter());
-
-        let args_array = self.ecx.expr_vec(self.macsp, args.collect());
+        let args_array = self.ecx.expr_vec(self.macsp, args);
 
         // Constructs an AST equivalent to:
         //
@@ -838,7 +826,7 @@ impl<'a, 'b> Context<'a, 'b> {
         // But the nested match expression is proved to perform not as well
         // as series of let's; the first approach does.
         let args_match = {
-            let pat = self.ecx.pat_tuple(self.macsp, pats);
+            let pat = self.ecx.pat_ident(self.macsp, Ident::new(sym::_args, self.macsp));
             let arm = self.ecx.arm(self.macsp, pat, args_array);
             let head = self.ecx.expr(self.macsp, ast::ExprKind::Tup(heads));
             self.ecx.expr_match(self.macsp, head, vec![arm])
@@ -877,10 +865,11 @@ impl<'a, 'b> Context<'a, 'b> {
         macsp: Span,
         mut sp: Span,
         ty: &ArgumentType,
-        arg: Ident,
+        arg_index: usize,
     ) -> P<ast::Expr> {
         sp = ecx.with_def_site_ctxt(sp);
-        let arg = ecx.expr_ident(sp, arg);
+        let arg = ecx.expr_ident(sp, Ident::new(sym::_args, sp));
+        let arg = ecx.expr(sp, ast::ExprKind::Field(arg, Ident::new(sym::integer(arg_index), sp)));
         let trait_ = match *ty {
             Placeholder(trait_) if trait_ == "<invalid>" => return DummyResult::raw_expr(sp, true),
             Placeholder(trait_) => trait_,

compiler/rustc_span/src/symbol.rs

@@ -271,6 +271,7 @@ symbols! {
         __S,
         __next,
         __try_var,
+        _args,
         _d,
         _e,
         _task_context,

src/test/pretty/dollar-crate.pp

@@ -12,7 +12,7 @@
     {
         ::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"],
                                                          &match () {
-                                                              () => [],
+                                                              _args => [],
                                                           }));
     };
 }

src/test/pretty/issue-4264.pp

@@ -45,7 +45,7 @@
                                                                                                                                                                      as
                                                                                                                                                                      ())
                                                                                                                                                                {
-                                                                                                                                                               ()
+                                                                                                                                                               _args
                                                                                                                                                                =>
                                                                                                                                                                ([]
                                                                                                                                                                    as

src/test/ui/attributes/key-value-expansion.stderr

@@ -19,8 +19,8 @@ error: unexpected token: `{
     let res =
         ::alloc::fmt::format(::core::fmt::Arguments::new_v1(&[""],
                                                             &match (&"u8",) {
-                                                                 (arg0,) =>
-                                                                 [::core::fmt::ArgumentV1::new(arg0,
+                                                                 _args =>
+                                                                 [::core::fmt::ArgumentV1::new(_args.0,
                                                                                                ::core::fmt::Display::fmt)],
                                                              }));
     res

src/test/ui/closures/print/closure-print-generic-trim-off-verbose-2.stderr

@@ -9,7 +9,7 @@ LL |         let c1 : () = c;
    |                  expected due to this
    |
    = note: expected unit type `()`
-                found closure `[mod1::f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#25t, extern "rust-call" fn(()), _#26t]]`
+                found closure `[mod1::f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#22t, extern "rust-call" fn(()), _#23t]]`
 help: use parentheses to call this closure
    |
 LL |         let c1 : () = c();

src/test/ui/closures/print/closure-print-generic-verbose-2.stderr

@@ -9,7 +9,7 @@ LL |         let c1 : () = c;
    |                  expected due to this
    |
    = note: expected unit type `()`
-                found closure `[f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#25t, extern "rust-call" fn(()), _#26t]]`
+                found closure `[f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#22t, extern "rust-call" fn(()), _#23t]]`
 help: use parentheses to call this closure
    |
 LL |         let c1 : () = c();

src/tools/clippy/clippy_utils/src/higher.rs

@@ -3,12 +3,12 @@
 #![deny(clippy::missing_docs_in_private_items)]
 
 use crate::ty::is_type_diagnostic_item;
-use crate::{is_expn_of, last_path_segment, match_def_path, path_to_local_id, paths};
+use crate::{is_expn_of, last_path_segment, match_def_path, paths};
 use if_chain::if_chain;
 use rustc_ast::ast::{self, LitKind};
 use rustc_hir as hir;
 use rustc_hir::{
-    Arm, Block, BorrowKind, Expr, ExprKind, HirId, LoopSource, MatchSource, Node, Pat, PatKind, QPath, StmtKind, UnOp,
+    Arm, Block, BorrowKind, Expr, ExprKind, HirId, LoopSource, MatchSource, Node, Pat, QPath, StmtKind, UnOp,
 };
 use rustc_lint::LateContext;
 use rustc_span::{sym, symbol, ExpnKind, Span, Symbol};
@@ -513,8 +513,6 @@ pub struct FormatArgsExpn<'tcx> {
     pub format_string_parts: &'tcx [Expr<'tcx>],
     /// Symbols corresponding to [`Self::format_string_parts`]
     pub format_string_symbols: Vec<Symbol>,
-    /// Match arm patterns, the `arg0`, etc. from the next field `args`
-    pub arg_names: &'tcx [Pat<'tcx>],
     /// Expressions like `ArgumentV1::new(arg0, Debug::fmt)`
     pub args: &'tcx [Expr<'tcx>],
     /// The final argument passed to `Arguments::new_v1_formatted`, if applicable
@@ -559,15 +557,13 @@ impl FormatArgsExpn<'tcx> {
                     _ => None,
                 })
                 .collect();
-            if let PatKind::Tuple(arg_names, None) = arm.pat.kind;
             if let ExprKind::Array(args) = arm.body.kind;
             then {
                 Some(FormatArgsExpn {
                     format_string_span: strs_ref.span,
                     value_args,
                     format_string_parts,
                     format_string_symbols,
-                    arg_names,
                     args,
                     fmt_expr,
                 })
@@ -594,10 +590,8 @@ impl FormatArgsExpn<'tcx> {
                             if let Ok(i) = usize::try_from(position);
                             let arg = &self.args[i];
                             if let ExprKind::Call(_, [arg_name, _]) = arg.kind;
-                            if let Some(j) = self
-                                .arg_names
-                                .iter()
-                                .position(|pat| path_to_local_id(arg_name, pat.hir_id));
+                            if let ExprKind::Field(_, j) = arg_name.kind;
+                            if let Ok(j) = j.name.as_str().parse::<usize>();
                             then {
                                 Some(FormatArgsArg { value: self.value_args[j], arg, fmt: Some(fmt) })
                             } else {