Simplify and robustly compute suggestion span using

`vis_span.to(ident.span.shrink_to_lo())`

compiler/rustc_lint/src/builtin.rs

@@ -41,7 +41,7 @@ pub use rustc_session::lint::builtin::*;
 use rustc_session::{declare_lint, declare_lint_pass, impl_lint_pass};
 use rustc_span::edition::Edition;
 use rustc_span::source_map::Spanned;
-use rustc_span::{BytePos, DUMMY_SP, Ident, InnerSpan, Span, Symbol, kw, sym};
+use rustc_span::{DUMMY_SP, Ident, InnerSpan, Span, Symbol, kw, sym};
 use rustc_target::asm::InlineAsmArch;
 use rustc_trait_selection::infer::{InferCtxtExt, TyCtxtInferExt};
 use rustc_trait_selection::traits::misc::type_allowed_to_implement_copy;
@@ -997,20 +997,12 @@ impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
                     self.check_no_mangle_on_generic_fn(cx, attr_span, it.owner_id.def_id);
                 }
             }
-            hir::ItemKind::Const(_, generics, ..) => {
+            hir::ItemKind::Const(ident, generics, ..) => {
                 if find_attr!(attrs, AttributeKind::NoMangle(..)) {
                     let suggestion =
                         if generics.params.is_empty() && generics.where_clause_span.is_empty() {
                             // account for "pub const" (#45562)
-                            let start = cx
-                                .tcx
-                                .sess
-                                .source_map()
-                                .span_to_snippet(it.span)
-                                .map(|snippet| snippet.find("const").unwrap_or(0))
-                                .unwrap_or(0) as u32;
-                            // `const` is 5 chars
-                            Some(it.span.with_hi(BytePos(it.span.lo().0 + start + 5)))
+                            Some(it.span.until(ident.span))
                         } else {
                             None
                         };

compiler/rustc_lint/src/lints.rs

@@ -229,7 +229,7 @@ pub(crate) struct BuiltinNoMangleGeneric {
 #[derive(LintDiagnostic)]
 #[diag(lint_builtin_const_no_mangle)]
 pub(crate) struct BuiltinConstNoMangle {
-    #[suggestion(code = "pub static", applicability = "machine-applicable")]
+    #[suggestion(code = "pub static ", applicability = "machine-applicable")]
     pub suggestion: Option<Span>,
 }
 

tests/ui/issues/issue-45562.stderr

@@ -2,7 +2,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/issue-45562.rs:5:14
    |
 LL | #[no_mangle] pub const RAH: usize = 5;
-   |              ---------^^^^^^^^^^^^^^^^
+   |              ----------^^^^^^^^^^^^^^^
    |              |
    |              help: try a static value: `pub static`
    |

tests/ui/lint/lint-unexported-no-mangle.stderr

@@ -31,7 +31,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/lint-unexported-no-mangle.rs:9:1
    |
 LL | const FOO: u64 = 1;
-   | -----^^^^^^^^^^^^^^
+   | ------^^^^^^^^^^^^^
    | |
    | help: try a static value: `pub static`
    |
@@ -41,7 +41,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/lint-unexported-no-mangle.rs:12:1
    |
 LL | pub const PUB_FOO: u64 = 1;
-   | ---------^^^^^^^^^^^^^^^^^^
+   | ----------^^^^^^^^^^^^^^^^^
    | |
    | help: try a static value: `pub static`
 

tests/ui/lint/suggestions.stderr

@@ -52,7 +52,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/suggestions.rs:6:14
    |
 LL | #[no_mangle] const DISCOVERY: usize = 1;
-   |              -----^^^^^^^^^^^^^^^^^^^^^^
+   |              ------^^^^^^^^^^^^^^^^^^^^^
    |              |
    |              help: try a static value: `pub static`
    |
@@ -81,7 +81,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/suggestions.rs:22:18
    |
 LL |     #[no_mangle] pub const DAUNTLESS: bool = true;
-   |                  ---------^^^^^^^^^^^^^^^^^^^^^^^^
+   |                  ----------^^^^^^^^^^^^^^^^^^^^^^^
    |                  |
    |                  help: try a static value: `pub static`
 
@@ -97,7 +97,7 @@ error: const items should never be `#[no_mangle]`
   --> $DIR/suggestions.rs:31:18
    |
 LL |     #[no_mangle] pub(crate) const VETAR: bool = true;
-   |                  ----------------^^^^^^^^^^^^^^^^^^^^
+   |                  -----------------^^^^^^^^^^^^^^^^^^^
    |                  |
    |                  help: try a static value: `pub static`