Added suggestion to function_item_references lint and fixed warning…

… message Also updated tests accordingly and tweaked some wording in the lint declaration.
rust-lang · Oct 27, 2020 · c791c64 · c791c64
1 parent 935fc36
commit c791c64
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Showing 4 changed files with 102 additions and 95 deletions.
diff --git a/compiler/rustc_mir/src/transform/function_item_references.rs b/compiler/rustc_mir/src/transform/function_item_references.rs
@@ -1,3 +1,4 @@
+use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
@@ -183,16 +184,22 @@ impl<'a, 'tcx> FunctionItemRefChecker<'a, 'tcx> {
         let variadic = if fn_sig.c_variadic() { ", ..." } else { "" };
         let ret = if fn_sig.output().skip_binder().is_unit() { "" } else { " -> _" };
         self.tcx.struct_span_lint_hir(FUNCTION_ITEM_REFERENCES, lint_root, span, |lint| {
-            lint.build(&format!(
-                "cast `{}` with `as {}{}fn({}{}){}` to obtain a function pointer",
-                ident,
-                unsafety,
-                abi,
-                vec!["_"; num_args].join(", "),
-                variadic,
-                ret,
-            ))
-            .emit();
+            lint.build("taking a reference to a function item does not give a function pointer")
+                .span_suggestion(
+                    span,
+                    &format!("cast `{}` to obtain a function pointer", ident),
+                    format!(
+                        "{} as {}{}fn({}{}){}",
+                        ident,
+                        unsafety,
+                        abi,
+                        vec!["_"; num_args].join(", "),
+                        variadic,
+                        ret,
+                    ),
+                    Applicability::Unspecified,
+                )
+                .emit();
         });
     }
 }
diff --git a/compiler/rustc_session/src/lint/builtin.rs b/compiler/rustc_session/src/lint/builtin.rs
@@ -2674,7 +2674,7 @@ declare_lint! {
     /// arguments bound by [`fmt::Pointer`] or transmuted.
     pub FUNCTION_ITEM_REFERENCES,
     Warn,
-    "suggest casting functions to pointers when attempting to take references",
+    "suggest casting to a function pointer when attempting to take references to function items",
 }
 
 declare_lint! {

diff --git a/src/test/ui/lint/function-item-references.rs b/src/test/ui/lint/function-item-references.rs
@@ -38,7 +38,7 @@ fn _format_assoc_item<T: HasItem>(data: T, f: &mut Formatter) -> std::fmt::Resul
 fn _call_pointer_fmt(f: &mut Formatter) -> std::fmt::Result {
     let zst_ref = &foo;
     Pointer::fmt(&zst_ref, f)
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
 }
 
 fn main() {
@@ -75,47 +75,47 @@ fn main() {
 
     //potential ways to incorrectly try printing function pointers
     println!("{:p}", &foo);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     print!("{:p}", &foo);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     format!("{:p}", &foo);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
 
     println!("{:p}", &foo as *const _);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", zst_ref);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", cast_zst_ptr);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", coerced_zst_ptr);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
 
     println!("{:p}", &fn_item);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", indirect_ref);
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
 
     println!("{:p}", &nop);
-    //~^ WARNING cast `nop` with `as fn()` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &bar);
-    //~^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &baz);
-    //~^ WARNING cast `baz` with `as fn(_, _) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &unsafe_fn);
-    //~^ WARNING cast `unsafe_fn` with `as unsafe fn()` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &c_fn);
-    //~^ WARNING cast `c_fn` with `as extern "C" fn()` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &unsafe_c_fn);
-    //~^ WARNING cast `unsafe_c_fn` with `as unsafe extern "C" fn()` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &variadic);
-    //~^ WARNING cast `variadic` with `as unsafe extern "C" fn(_, ...)` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     println!("{:p}", &std::env::var::<String>);
-    //~^ WARNING cast `var` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
 
     println!("{:p} {:p} {:p}", &nop, &foo, &bar);
-    //~^ WARNING cast `nop` with `as fn()` to obtain a function pointer
-    //~^^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
-    //~^^^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
+    //~^^ WARNING taking a reference to a function item does not give a function pointer
+    //~^^^ WARNING taking a reference to a function item does not give a function pointer
 
     //using a function reference to call a function shouldn't lint
     (&bar)(1);
@@ -128,10 +128,10 @@ fn main() {
     unsafe {
         //potential ways to incorrectly try transmuting function pointers
         std::mem::transmute::<_, usize>(&foo);
-        //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
+        //~^ WARNING taking a reference to a function item does not give a function pointer
         std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
-        //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
-        //~^^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+        //~^ WARNING taking a reference to a function item does not give a function pointer
+        //~^^ WARNING taking a reference to a function item does not give a function pointer
 
         //the correct way to transmute function pointers
         std::mem::transmute::<_, usize>(foo as fn() -> u32);
@@ -140,12 +140,12 @@ fn main() {
 
     //function references as arguments required to be bound by std::fmt::Pointer should lint
     print_ptr(&bar);
-    //~^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     bound_by_ptr_trait(&bar);
-    //~^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
     bound_by_ptr_trait_tuple((&foo, &bar));
-    //~^ WARNING cast `foo` with `as fn() -> _` to obtain a function pointer
-    //~^^ WARNING cast `bar` with `as fn(_) -> _` to obtain a function pointer
+    //~^ WARNING taking a reference to a function item does not give a function pointer
+    //~^^ WARNING taking a reference to a function item does not give a function pointer
     implicit_ptr_trait(&bar); // ignore
 
     //correct ways to pass function pointers as arguments bound by std::fmt::Pointer

diff --git a/src/test/ui/lint/function-item-references.stderr b/src/test/ui/lint/function-item-references.stderr
@@ -1,176 +1,176 @@
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:40:18
    |
 LL |     Pointer::fmt(&zst_ref, f)
-   |                  ^^^^^^^^
+   |                  ^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
    |
 note: the lint level is defined here
   --> $DIR/function-item-references.rs:3:9
    |
 LL | #![warn(function_item_references)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:77:22
    |
 LL |     println!("{:p}", &foo);
-   |                      ^^^^
+   |                      ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:79:20
    |
 LL |     print!("{:p}", &foo);
-   |                    ^^^^
+   |                    ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:81:21
    |
 LL |     format!("{:p}", &foo);
-   |                     ^^^^
+   |                     ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:84:22
    |
 LL |     println!("{:p}", &foo as *const _);
-   |                      ^^^^^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:86:22
    |
 LL |     println!("{:p}", zst_ref);
-   |                      ^^^^^^^
+   |                      ^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:88:22
    |
 LL |     println!("{:p}", cast_zst_ptr);
-   |                      ^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:90:22
    |
 LL |     println!("{:p}", coerced_zst_ptr);
-   |                      ^^^^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:93:22
    |
 LL |     println!("{:p}", &fn_item);
-   |                      ^^^^^^^^
+   |                      ^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:95:22
    |
 LL |     println!("{:p}", indirect_ref);
-   |                      ^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `nop` with `as fn()` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:98:22
    |
 LL |     println!("{:p}", &nop);
-   |                      ^^^^
+   |                      ^^^^ help: cast `nop` to obtain a function pointer: `nop as fn()`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:100:22
    |
 LL |     println!("{:p}", &bar);
-   |                      ^^^^
+   |                      ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `baz` with `as fn(_, _) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:102:22
    |
 LL |     println!("{:p}", &baz);
-   |                      ^^^^
+   |                      ^^^^ help: cast `baz` to obtain a function pointer: `baz as fn(_, _) -> _`
 
-warning: cast `unsafe_fn` with `as unsafe fn()` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:104:22
    |
 LL |     println!("{:p}", &unsafe_fn);
-   |                      ^^^^^^^^^^
+   |                      ^^^^^^^^^^ help: cast `unsafe_fn` to obtain a function pointer: `unsafe_fn as unsafe fn()`
 
-warning: cast `c_fn` with `as extern "C" fn()` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:106:22
    |
 LL |     println!("{:p}", &c_fn);
-   |                      ^^^^^
+   |                      ^^^^^ help: cast `c_fn` to obtain a function pointer: `c_fn as extern "C" fn()`
 
-warning: cast `unsafe_c_fn` with `as unsafe extern "C" fn()` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:108:22
    |
 LL |     println!("{:p}", &unsafe_c_fn);
-   |                      ^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^ help: cast `unsafe_c_fn` to obtain a function pointer: `unsafe_c_fn as unsafe extern "C" fn()`
 
-warning: cast `variadic` with `as unsafe extern "C" fn(_, ...)` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:110:22
    |
 LL |     println!("{:p}", &variadic);
-   |                      ^^^^^^^^^
+   |                      ^^^^^^^^^ help: cast `variadic` to obtain a function pointer: `variadic as unsafe extern "C" fn(_, ...)`
 
-warning: cast `var` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:112:22
    |
 LL |     println!("{:p}", &std::env::var::<String>);
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ help: cast `var` to obtain a function pointer: `var as fn(_) -> _`
 
-warning: cast `nop` with `as fn()` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:115:32
    |
 LL |     println!("{:p} {:p} {:p}", &nop, &foo, &bar);
-   |                                ^^^^
+   |                                ^^^^ help: cast `nop` to obtain a function pointer: `nop as fn()`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:115:38
    |
 LL |     println!("{:p} {:p} {:p}", &nop, &foo, &bar);
-   |                                      ^^^^
+   |                                      ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:115:44
    |
 LL |     println!("{:p} {:p} {:p}", &nop, &foo, &bar);
-   |                                            ^^^^
+   |                                            ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:130:41
    |
 LL |         std::mem::transmute::<_, usize>(&foo);
-   |                                         ^^^^
+   |                                         ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:132:50
    |
 LL |         std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
-   |                                                  ^^^^^^^^^^^^
+   |                                                  ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:132:50
    |
 LL |         std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
-   |                                                  ^^^^^^^^^^^^
+   |                                                  ^^^^^^^^^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:142:15
    |
 LL |     print_ptr(&bar);
-   |               ^^^^
+   |               ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:144:24
    |
 LL |     bound_by_ptr_trait(&bar);
-   |                        ^^^^
+   |                        ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `bar` with `as fn(_) -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:146:30
    |
 LL |     bound_by_ptr_trait_tuple((&foo, &bar));
-   |                              ^^^^^^^^^^^^
+   |                              ^^^^^^^^^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
 
-warning: cast `foo` with `as fn() -> _` to obtain a function pointer
+warning: taking a reference to a function item does not give a function pointer
   --> $DIR/function-item-references.rs:146:30
    |
 LL |     bound_by_ptr_trait_tuple((&foo, &bar));
-   |                              ^^^^^^^^^^^^
+   |                              ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
 
 warning: 28 warnings emitted