Rollup merge of #114550 - dtolnay:globalalloc, r=compiler-errors

Generate better function argument names in global_allocator expansion

Generated code for `#[global_allocator] static ALLOCATOR: Allocator = Allocator;`—

**Before:**

```rust
const _: () = {
    #[rustc_std_internal_symbol]
    unsafe fn __rust_alloc(arg0: usize, arg1: usize) -> *mut u8 {
        ::core::alloc::GlobalAlloc::alloc(
            &ALLOCATOR,
            ::core::alloc::Layout::from_size_align_unchecked(arg0, arg1),
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_dealloc(arg0: *mut u8, arg1: usize, arg2: usize) -> () {
        ::core::alloc::GlobalAlloc::dealloc(
            &ALLOCATOR,
            arg0,
            ::core::alloc::Layout::from_size_align_unchecked(arg1, arg2),
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_realloc(
        arg0: *mut u8,
        arg1: usize,
        arg2: usize,
        arg3: usize,
    ) -> *mut u8 {
        ::core::alloc::GlobalAlloc::realloc(
            &ALLOCATOR,
            arg0,
            ::core::alloc::Layout::from_size_align_unchecked(arg1, arg2),
            arg3,
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_alloc_zeroed(arg0: usize, arg1: usize) -> *mut u8 {
        ::core::alloc::GlobalAlloc::alloc_zeroed(
            &ALLOCATOR,
            ::core::alloc::Layout::from_size_align_unchecked(arg0, arg1),
        )
    }
};
```

**After:**

```rust
const _: () = {
    #[rustc_std_internal_symbol]
    unsafe fn __rust_alloc(size: usize, align: usize) -> *mut u8 {
        ::core::alloc::GlobalAlloc::alloc(
            &ALLOCATOR,
            ::core::alloc::Layout::from_size_align_unchecked(size, align),
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize) -> () {
        ::core::alloc::GlobalAlloc::dealloc(
            &ALLOCATOR,
            ptr,
            ::core::alloc::Layout::from_size_align_unchecked(size, align),
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_realloc(
        ptr: *mut u8,
        size: usize,
        align: usize,
        new_size: usize,
    ) -> *mut u8 {
        ::core::alloc::GlobalAlloc::realloc(
            &ALLOCATOR,
            ptr,
            ::core::alloc::Layout::from_size_align_unchecked(size, align),
            new_size,
        )
    }
    #[rustc_std_internal_symbol]
    unsafe fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8 {
        ::core::alloc::GlobalAlloc::alloc_zeroed(
            &ALLOCATOR,
            ::core::alloc::Layout::from_size_align_unchecked(size, align),
        )
    }
};
```

compiler/rustc_ast/src/expand/allocator.rs

@@ -33,29 +33,41 @@ pub enum AllocatorTy {
 
 pub struct AllocatorMethod {
     pub name: Symbol,
-    pub inputs: &'static [AllocatorTy],
+    pub inputs: &'static [AllocatorMethodInput],
     pub output: AllocatorTy,
 }
 
+pub struct AllocatorMethodInput {
+    pub name: &'static str,
+    pub ty: AllocatorTy,
+}
+
 pub static ALLOCATOR_METHODS: &[AllocatorMethod] = &[
     AllocatorMethod {
         name: sym::alloc,
-        inputs: &[AllocatorTy::Layout],
+        inputs: &[AllocatorMethodInput { name: "layout", ty: AllocatorTy::Layout }],
         output: AllocatorTy::ResultPtr,
     },
     AllocatorMethod {
         name: sym::dealloc,
-        inputs: &[AllocatorTy::Ptr, AllocatorTy::Layout],
+        inputs: &[
+            AllocatorMethodInput { name: "ptr", ty: AllocatorTy::Ptr },
+            AllocatorMethodInput { name: "layout", ty: AllocatorTy::Layout },
+        ],
         output: AllocatorTy::Unit,
     },
     AllocatorMethod {
         name: sym::realloc,
-        inputs: &[AllocatorTy::Ptr, AllocatorTy::Layout, AllocatorTy::Usize],
+        inputs: &[
+            AllocatorMethodInput { name: "ptr", ty: AllocatorTy::Ptr },
+            AllocatorMethodInput { name: "layout", ty: AllocatorTy::Layout },
+            AllocatorMethodInput { name: "new_size", ty: AllocatorTy::Usize },
+        ],
         output: AllocatorTy::ResultPtr,
     },
     AllocatorMethod {
         name: sym::alloc_zeroed,
-        inputs: &[AllocatorTy::Layout],
+        inputs: &[AllocatorMethodInput { name: "layout", ty: AllocatorTy::Layout }],
         output: AllocatorTy::ResultPtr,
     },
 ];

compiler/rustc_builtin_macros/src/global_allocator.rs

@@ -2,7 +2,7 @@ use crate::util::check_builtin_macro_attribute;
 
 use crate::errors;
 use rustc_ast::expand::allocator::{
-    global_fn_name, AllocatorMethod, AllocatorTy, ALLOCATOR_METHODS,
+    global_fn_name, AllocatorMethod, AllocatorMethodInput, AllocatorTy, ALLOCATOR_METHODS,
 };
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, AttrVec, Expr, FnHeader, FnSig, Generics, Param, StmtKind};
@@ -70,13 +70,7 @@ struct AllocFnFactory<'a, 'b> {
 impl AllocFnFactory<'_, '_> {
     fn allocator_fn(&self, method: &AllocatorMethod) -> Stmt {
         let mut abi_args = ThinVec::new();
-        let mut i = 0;
+        let args = method.inputs.iter().map(|input| self.arg_ty(input, &mut abi_args)).collect();
-        let mut mk = || {
-            let name = Ident::from_str_and_span(&format!("arg{i}"), self.span);
-            i += 1;
-            name
-        };
-        let args = method.inputs.iter().map(|ty| self.arg_ty(ty, &mut abi_args, &mut mk)).collect();
         let result = self.call_allocator(method.name, args);
         let output_ty = self.ret_ty(&method.output);
         let decl = self.cx.fn_decl(abi_args, ast::FnRetTy::Ty(output_ty));
@@ -113,18 +107,19 @@ impl AllocFnFactory<'_, '_> {
         thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
     }
 
-    fn arg_ty(
+    fn arg_ty(&self, input: &AllocatorMethodInput, args: &mut ThinVec<Param>) -> P<Expr> {
-        &self,
+        match input.ty {
-        ty: &AllocatorTy,
-        args: &mut ThinVec<Param>,
-        ident: &mut dyn FnMut() -> Ident,
-    ) -> P<Expr> {
-        match *ty {
             AllocatorTy::Layout => {
+                // If an allocator method is ever introduced having multiple
+                // Layout arguments, these argument names need to be
+                // disambiguated somehow. Currently the generated code would
+                // fail to compile with "identifier is bound more than once in
+                // this parameter list".
+                let size = Ident::from_str_and_span("size", self.span);
+                let align = Ident::from_str_and_span("align", self.span);
+
                 let usize = self.cx.path_ident(self.span, Ident::new(sym::usize, self.span));
                 let ty_usize = self.cx.ty_path(usize);
-                let size = ident();
-                let align = ident();
                 args.push(self.cx.param(self.span, size, ty_usize.clone()));
                 args.push(self.cx.param(self.span, align, ty_usize));
 
@@ -138,13 +133,13 @@ impl AllocFnFactory<'_, '_> {
             }
 
             AllocatorTy::Ptr => {
-                let ident = ident();
+                let ident = Ident::from_str_and_span(input.name, self.span);
                 args.push(self.cx.param(self.span, ident, self.ptr_u8()));
                 self.cx.expr_ident(self.span, ident)
             }
 
             AllocatorTy::Usize => {
-                let ident = ident();
+                let ident = Ident::from_str_and_span(input.name, self.span);
                 args.push(self.cx.param(self.span, ident, self.usize()));
                 self.cx.expr_ident(self.span, ident)
             }

compiler/rustc_codegen_cranelift/src/allocator.rs

@@ -39,8 +39,8 @@ fn codegen_inner(
     if kind == AllocatorKind::Default {
         for method in ALLOCATOR_METHODS {
             let mut arg_tys = Vec::with_capacity(method.inputs.len());
-            for ty in method.inputs.iter() {
+            for input in method.inputs.iter() {
-                match *ty {
+                match input.ty {
                     AllocatorTy::Layout => {
                         arg_tys.push(usize_ty); // size
                         arg_tys.push(usize_ty); // align

compiler/rustc_codegen_gcc/src/allocator.rs

@@ -27,8 +27,8 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_nam
     if kind == AllocatorKind::Default {
         for method in ALLOCATOR_METHODS {
             let mut types = Vec::with_capacity(method.inputs.len());
-            for ty in method.inputs.iter() {
+            for input in method.inputs.iter() {
-                match *ty {
+                match input.ty {
                     AllocatorTy::Layout => {
                         types.push(usize);
                         types.push(usize);

compiler/rustc_codegen_llvm/src/allocator.rs

@@ -34,8 +34,8 @@ pub(crate) unsafe fn codegen(
     if kind == AllocatorKind::Default {
         for method in ALLOCATOR_METHODS {
             let mut args = Vec::with_capacity(method.inputs.len());
-            for ty in method.inputs.iter() {
+            for input in method.inputs.iter() {
-                match *ty {
+                match input.ty {
                     AllocatorTy::Layout => {
                         args.push(usize); // size
                         args.push(usize); // align