Remove match-less special case in format_args!() expansion.

Author: m-ou-se

compiler/rustc_ast_lowering/src/format.rs

@@ -1,6 +1,4 @@
 use super::LoweringContext;
-use rustc_ast as ast;
-use rustc_ast::visit::{self, Visitor};
 use rustc_ast::*;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
@@ -190,37 +188,10 @@ fn expand_format_args<'hir>(
         ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
     });
 
-    let arguments = fmt.arguments.all_args();
-
-    // If the args array contains exactly all the original arguments once,
-    // in order, we can use a simple array instead of a `match` construction.
-    // However, if there's a yield point in any argument except the first one,
-    // we don't do this, because an ArgumentV1 cannot be kept across yield points.
-    let use_simple_array = argmap.len() == arguments.len()
-        && argmap.iter().enumerate().all(|(i, &(j, _))| i == j)
-        && arguments.iter().skip(1).all(|arg| !may_contain_yield_point(&arg.expr));
-
-    let args = if use_simple_array {
+    let args = if fmt.arguments.all_args().is_empty() {
         // Generate:
-        //     &[
-        //         ::core::fmt::ArgumentV1::new_display(&arg0),
-        //         ::core::fmt::ArgumentV1::new_lower_hex(&arg1),
-        //         ::core::fmt::ArgumentV1::new_debug(&arg2),
-        //     ]
-        let elements: Vec<_> = arguments
-            .iter()
-            .zip(argmap)
-            .map(|(arg, (_, ty))| {
-                let sp = arg.expr.span.with_ctxt(macsp.ctxt());
-                let arg = ctx.lower_expr(&arg.expr);
-                let ref_arg = ctx.arena.alloc(ctx.expr(
-                    sp,
-                    hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, arg),
-                ));
-                make_argument(ctx, sp, ref_arg, ty)
-            })
-            .collect();
-        ctx.expr_array_ref(macsp, ctx.arena.alloc_from_iter(elements))
+        //     &[]
+        ctx.expr_array_ref(macsp, &[])
     } else {
         // Generate:
         //     &match (&arg0, &arg1, &arg2) {
@@ -233,7 +204,7 @@ fn expand_format_args<'hir>(
         let args_ident = Ident::new(sym::args, macsp);
         let (args_pat, args_hir_id) = ctx.pat_ident(macsp, args_ident);
         let args = ctx.arena.alloc_from_iter(argmap.iter().map(|&(arg_index, ty)| {
-            if let Some(arg) = arguments.get(arg_index) {
+            if let Some(arg) = fmt.arguments.all_args().get(arg_index) {
                 let sp = arg.expr.span.with_ctxt(macsp.ctxt());
                 let args_ident_expr = ctx.expr_ident(macsp, args_ident, args_hir_id);
                 let arg = ctx.arena.alloc(ctx.expr(
@@ -248,7 +219,9 @@ fn expand_format_args<'hir>(
                 ctx.expr(macsp, hir::ExprKind::Err)
             }
         }));
-        let elements: Vec<_> = arguments
+        let elements: Vec<_> = fmt
+            .arguments
+            .all_args()
             .iter()
             .map(|arg| {
                 let arg_expr = ctx.lower_expr(&arg.expr);
@@ -320,35 +293,3 @@ fn expand_format_args<'hir>(
         hir::ExprKind::Call(new_v1, new_args)
     }
 }
-
-fn may_contain_yield_point(e: &ast::Expr) -> bool {
-    struct MayContainYieldPoint(bool);
-
-    impl Visitor<'_> for MayContainYieldPoint {
-        fn visit_expr(&mut self, e: &ast::Expr) {
-            if let ast::ExprKind::Await(_) | ast::ExprKind::Yield(_) = e.kind {
-                self.0 = true;
-            } else {
-                visit::walk_expr(self, e);
-            }
-        }
-
-        fn visit_mac_call(&mut self, _: &ast::MacCall) {
-            self.0 = true;
-        }
-
-        fn visit_attribute(&mut self, _: &ast::Attribute) {
-            // Conservatively assume this may be a proc macro attribute in
-            // expression position.
-            self.0 = true;
-        }
-
-        fn visit_item(&mut self, _: &ast::Item) {
-            // Do not recurse into nested items.
-        }
-    }
-
-    let mut visitor = MayContainYieldPoint(false);
-    visitor.visit_expr(e);
-    visitor.0
-}

tests/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, _#16t, extern "rust-call" fn(()), _#15t]]`
+                found closure `[mod1::f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#19t, extern "rust-call" fn(()), _#18t]]`
 help: use parentheses to call this closure
    |
 LL |         let c1 : () = c();

tests/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, _#16t, extern "rust-call" fn(()), _#15t]]`
+                found closure `[f<T>::{closure#0} closure_substs=(unavailable) substs=[T, _#19t, extern "rust-call" fn(()), _#18t]]`
 help: use parentheses to call this closure
    |
 LL |         let c1 : () = c();

tests/ui/issues/issue-69455.stderr

@@ -1,14 +1,16 @@
-error[E0282]: type annotations needed
-  --> $DIR/issue-69455.rs:29:20
+error[E0284]: type annotations needed
+  --> $DIR/issue-69455.rs:29:41
    |
 LL |     println!("{}", 23u64.test(xs.iter().sum()));
-   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the associated function `new_display`
+   |                          ----           ^^^ cannot infer type of the type parameter `S` declared on the associated function `sum`
+   |                          |
+   |                          type must be known at this point
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: cannot satisfy `<u64 as Test<_>>::Output == _`
 help: consider specifying the generic argument
    |
-LL |     println!("{}", 23u64.test(xs.iter().sum())::<T>);
-   |                                               +++++
+LL |     println!("{}", 23u64.test(xs.iter().sum::<S>()));
+   |                                            +++++
 
 error[E0283]: type annotations needed
   --> $DIR/issue-69455.rs:29:41
@@ -33,5 +35,5 @@ LL |     println!("{}", 23u64.test(xs.iter().sum::<S>()));
 
 error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0283.
-For more information about an error, try `rustc --explain E0282`.
+Some errors have detailed explanations: E0283, E0284.
+For more information about an error, try `rustc --explain E0283`.