in which the private no-mangle lints receive a valued lesson in humility

The incompetent fool who added these suggestions in 38e5a96 apparently
thought it was safe to assume that, because the offending function or
static was unreachable, it would therefore have not have any existing
visibility modifiers, making it safe for us to unconditionally suggest
inserting `pub`. This isn't true.

This resolves #47383.

Author: zackmdavis

src/librustc_lint/builtin.rs

@@ -1154,9 +1154,11 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
                         let msg = "function is marked #[no_mangle], but not exported";
                         let mut err = cx.struct_span_lint(PRIVATE_NO_MANGLE_FNS, it.span, msg);
                         let insertion_span = it.span.with_hi(it.span.lo());
-                        err.span_suggestion(insertion_span,
-                                            "try making it public",
-                                            "pub ".to_owned());
+                        if it.vis == hir::Visibility::Inherited {
+                            err.span_suggestion(insertion_span,
+                                                "try making it public",
+                                                "pub ".to_owned());
+                        }
                         err.emit();
                     }
                     if generics.is_type_parameterized() {
@@ -1177,9 +1179,11 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
                        let msg = "static is marked #[no_mangle], but not exported";
                        let mut err = cx.struct_span_lint(PRIVATE_NO_MANGLE_STATICS, it.span, msg);
                        let insertion_span = it.span.with_hi(it.span.lo());
-                       err.span_suggestion(insertion_span,
-                                           "try making it public",
-                                           "pub ".to_owned());
+                       if it.vis == hir::Visibility::Inherited {
+                           err.span_suggestion(insertion_span,
+                                               "try making it public",
+                                               "pub ".to_owned());
+                       }
                        err.emit();
                 }
             }

src/test/ui/lint/suggestions.rs

@@ -24,6 +24,16 @@ pub fn defiant<T>(_t: T) {}
 fn rio_grande() {} // should suggest `pub`
 //~^ WARN function is marked
 
+mod badlands {
+    // The private-no-mangle lints shouldn't suggest inserting `pub` when the
+    // item is already `pub` (but triggered the lint because, e.g., it's in a
+    // private module). (Issue #47383)
+    #[no_mangle] pub static DAUNTLESS: bool = true;
+    //~^ WARN static is marked
+    #[no_mangle] pub fn val_jean() {}
+    //~^ WARN function is marked
+}
+
 struct Equinox {
     warp_factor: f32,
 }

src/test/ui/lint/suggestions.stderr

@@ -1,7 +1,7 @@
 warning: unnecessary parentheses around assigned value
-  --> $DIR/suggestions.rs:36:21
+  --> $DIR/suggestions.rs:46:21
    |
-36 |         let mut a = (1); // should suggest no `mut`, no parens
+46 |         let mut a = (1); // should suggest no `mut`, no parens
    |                     ^^^ help: remove these parentheses
    |
 note: lint level defined here
@@ -11,17 +11,17 @@ note: lint level defined here
    |                     ^^^^^^^^^^^^^
 
 warning: use of deprecated attribute `no_debug`: the `#[no_debug]` attribute was an experimental feature that has been deprecated due to lack of demand. See https://github.com/rust-lang/rust/issues/29721
-  --> $DIR/suggestions.rs:31:1
+  --> $DIR/suggestions.rs:41:1
    |
-31 | #[no_debug] // should suggest removal of deprecated attribute
+41 | #[no_debug] // should suggest removal of deprecated attribute
    | ^^^^^^^^^^^ help: remove this attribute
    |
    = note: #[warn(deprecated)] on by default
 
 warning: variable does not need to be mutable
-  --> $DIR/suggestions.rs:36:13
+  --> $DIR/suggestions.rs:46:13
    |
-36 |         let mut a = (1); // should suggest no `mut`, no parens
+46 |         let mut a = (1); // should suggest no `mut`, no parens
    |             ---^^
    |             |
    |             help: remove this `mut`
@@ -72,18 +72,30 @@ warning: function is marked #[no_mangle], but not exported
    |
    = note: #[warn(private_no_mangle_fns)] on by default
 
+warning: static is marked #[no_mangle], but not exported
+  --> $DIR/suggestions.rs:31:18
+   |
+31 |     #[no_mangle] pub static DAUNTLESS: bool = true;
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: function is marked #[no_mangle], but not exported
+  --> $DIR/suggestions.rs:33:18
+   |
+33 |     #[no_mangle] pub fn val_jean() {}
+   |                  ^^^^^^^^^^^^^^^^^^^^
+
 warning: denote infinite loops with `loop { ... }`
-  --> $DIR/suggestions.rs:34:5
+  --> $DIR/suggestions.rs:44:5
    |
-34 |     while true { // should suggest `loop`
+44 |     while true { // should suggest `loop`
    |     ^^^^^^^^^^ help: use `loop`
    |
    = note: #[warn(while_true)] on by default
 
 warning: the `warp_factor:` in this pattern is redundant
-  --> $DIR/suggestions.rs:41:23
+  --> $DIR/suggestions.rs:51:23
    |
-41 |             Equinox { warp_factor: warp_factor } => {} // should suggest shorthand
+51 |             Equinox { warp_factor: warp_factor } => {} // should suggest shorthand
    |                       ------------^^^^^^^^^^^^
    |                       |
    |                       help: remove this