Suppress crate-root help when attribute is in same file

Skip the "the crate root is at ..." help message when the misplaced
crate-level attribute is already in the crate root file, since it
adds no useful information in that case. Add a cross-file test to
verify the help still appears when the attribute is in a different
file from the crate root.

Author: Dnreikronos

compiler/rustc_attr_parsing/src/target_checking.rs

@@ -5,7 +5,7 @@ use rustc_errors::{DiagArgValue, Diagnostic, MultiSpan, StashKey};
 use rustc_feature::Features;
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::{AttrItem, Attribute, MethodKind, Target};
-use rustc_span::{BytePos, RemapPathScopeComponents, Span, Symbol, sym};
+use rustc_span::{BytePos, FileName, RemapPathScopeComponents, Span, Symbol, sym};
 
 use crate::AttributeParser;
 use crate::context::AcceptContext;
@@ -189,6 +189,12 @@ impl<'sess> AttributeParser<'sess> {
         let (show_crate_root_help, crate_root_path) = is_used_as_inner
             .then(|| cx.cx.sess.local_crate_source_file())
             .flatten()
+            .filter(|src| {
+                !matches!(
+                    cx.cx.sess.source_map().span_to_filename(attr_span),
+                    FileName::Real(ref name) if name == src
+                )
+            })
             .map(|src| {
                 (true, src.path(RemapPathScopeComponents::DIAGNOSTICS).display().to_string())
             })

tests/ui/attributes/attr-mix-new.stderr

@@ -4,7 +4,6 @@ warning: the `#![feature]` attribute can only be used at the crate root
 LL |   #![feature(globs)]
    |   ^^^^^^^^^^^^^^^^^^
    |
-   = help: the crate root is at `$DIR/attr-mix-new.rs`
    = note: requested on the command line with `-W unused-attributes`
 
 warning: 1 warning emitted

tests/ui/attributes/crate-only-as-outer.stderr

@@ -21,8 +21,6 @@ error: the `#![crate_name]` attribute can only be used at the crate root
    |
 LL |     #![crate_name = "iwi"]
    |     ^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: the crate root is at `$DIR/crate-only-as-outer.rs`
 
 error: aborting due to 2 previous errors
 

tests/ui/attributes/crate-root-path-in-different-file/crate-root-path-in-different-file.rs

@@ -0,0 +1,7 @@
+#![deny(unused_attributes)]
+
+mod submod;
+
+fn main() {}
+
+//~? ERROR the `#![crate_name]` attribute can only be used at the crate root

tests/ui/attributes/crate-root-path-in-different-file/crate-root-path-in-different-file.stderr

@@ -0,0 +1,15 @@
+error: the `#![crate_name]` attribute can only be used at the crate root
+  --> $DIR/submod.rs:1:1
+   |
+LL | #![crate_name = "bar"]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: the crate root is at `$DIR/crate-root-path-in-different-file.rs`
+note: the lint level is defined here
+  --> $DIR/crate-root-path-in-different-file.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/attributes/crate-root-path-in-different-file/submod.rs

@@ -0,0 +1 @@
+#![crate_name = "bar"]

tests/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs

@@ -503,7 +503,6 @@ mod no_std {
     //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![no_std] }
 //~^ WARN the `#![no_std]` attribute can only be used at the crate root
-//~| HELP the crate root is at
 
     #[no_std] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
@@ -765,8 +764,7 @@ mod windows_subsystem {
     //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![windows_subsystem="windows"] }
     //~^ WARN the `#![windows_subsystem]` attribute can only be used at the crate root
-    //~| HELP the crate root is at
-
+    
     #[windows_subsystem = "windows"] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
     //~| NOTE this attribute does not have an `!`, which means it is applied to this function
@@ -792,7 +790,6 @@ mod crate_name {
 //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![crate_name="0900"] }
 //~^ WARN the `#![crate_name]` attribute can only be used at the crate root
-//~| HELP the crate root is at
 
     #[crate_name = "0900"] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
@@ -817,7 +814,6 @@ mod crate_type {
 //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![crate_type="0800"] }
 //~^ WARN the `#![crate_type]` attribute can only be used at the crate root
-//~| HELP the crate root is at
 
     #[crate_type = "0800"] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
@@ -842,8 +838,7 @@ mod feature {
 //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![feature(x0600)] }
     //~^ WARN the `#![feature]` attribute can only be used at the crate root
-    //~| HELP the crate root is at
-
+    
     #[feature(x0600)] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
     //~| NOTE this attribute does not have an `!`, which means it is applied to this function
@@ -868,8 +863,7 @@ mod no_main_1 {
     //~^ NOTE: this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![no_main] }
     //~^ WARN the `#![no_main]` attribute can only be used at the crate root
-    //~| HELP the crate root is at
-
+    
     #[no_main] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
     //~| NOTE this attribute does not have an `!`, which means it is applied to this function
@@ -893,8 +887,7 @@ mod no_builtins {
     //~^ NOTE: this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![no_builtins] }
     //~^ WARN the `#![no_builtins]` attribute can only be used at the crate root
-    //~| HELP the crate root is at
-
+    
     #[no_builtins] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
     //~| NOTE this attribute does not have an `!`, which means it is applied to this function
@@ -918,7 +911,6 @@ mod recursion_limit {
     //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![recursion_limit="0200"] }
 //~^ WARN the `#![recursion_limit]` attribute can only be used at the crate root
-//~| HELP the crate root is at
 
     #[recursion_limit="0200"] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
@@ -943,7 +935,6 @@ mod type_length_limit {
     //~^ NOTE this attribute does not have an `!`, which means it is applied to this module
     mod inner { #![type_length_limit="0100"] }
 //~^ WARN the `#![type_length_limit]` attribute can only be used at the crate root
-//~| HELP the crate root is at
 
     #[type_length_limit="0100"] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute