Fix suggestion when there were a colon already in generics

compiler/rustc_trait_selection/src/error_reporting/infer/region.rs

@@ -774,20 +774,31 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     // instead we suggest `T: 'a + 'b` in that case.
                     let hir_generics = self.tcx.hir_get_generics(scope).unwrap();
                     let sugg_span = match hir_generics.bounds_span_for_suggestions(def_id) {
-                        Some((span, open_paren_sp)) => Some((span, true, open_paren_sp)),
+                        Some((span, open_paren_sp)) => {
+                            Some((span, LifetimeSuggestion::NeedsPlus(open_paren_sp)))
+                        }
                         // If `param` corresponds to `Self`, no usable suggestion span.
                         None if generics.has_self && param.index == 0 => None,
                         None => {
+                            let mut colon_flag = false;
                             let span = if let Some(param) =
                                 hir_generics.params.iter().find(|param| param.def_id == def_id)
                                 && let ParamName::Plain(ident) = param.name
                             {
-                                ident.span.shrink_to_hi()
+                                if let Some(sp) = param.colon_span {
+                                    colon_flag = true;
+                                    sp.shrink_to_hi()
+                                } else {
+                                    ident.span.shrink_to_hi()
+                                }
                             } else {
                                 let span = self.tcx.def_span(def_id);
                                 span.shrink_to_hi()
                             };
-                            Some((span, false, None))
+                            match colon_flag {
+                                true => Some((span, LifetimeSuggestion::HasColon)),
+                                false => Some((span, LifetimeSuggestion::NeedsColon)),
+                            }
                         }
                     };
                     (scope, sugg_span)
@@ -811,17 +822,21 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             let mut suggs = vec![];
             let lt_name = self.suggest_name_region(generic_param_scope, sub, &mut suggs);
 
-            if let Some((sp, has_lifetimes, open_paren_sp)) = type_param_sugg_span
+            if let Some((sp, suggestion_type)) = type_param_sugg_span
                 && suggestion_scope == type_scope
             {
-                let suggestion =
-                    if has_lifetimes { format!(" + {lt_name}") } else { format!(": {lt_name}") };
-
-                if let Some(open_paren_sp) = open_paren_sp {
-                    suggs.push((open_paren_sp, "(".to_string()));
-                    suggs.push((sp, format!("){suggestion}")));
-                } else {
-                    suggs.push((sp, suggestion))
+                match suggestion_type {
+                    LifetimeSuggestion::NeedsPlus(open_paren_sp) => {
+                        let suggestion = format!(" + {lt_name}");
+                        if let Some(open_paren_sp) = open_paren_sp {
+                            suggs.push((open_paren_sp, "(".to_string()));
+                            suggs.push((sp, format!("){suggestion}")));
+                        } else {
+                            suggs.push((sp, suggestion));
+                        }
+                    }
+                    LifetimeSuggestion::NeedsColon => suggs.push((sp, format!(": {lt_name}"))),
+                    LifetimeSuggestion::HasColon => suggs.push((sp, format!(" {lt_name}"))),
                 }
             } else if let GenericKind::Alias(ref p) = bound_kind
                 && let ty::Projection = p.kind(self.tcx)
@@ -1056,6 +1071,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     }
 }
 
+enum LifetimeSuggestion {
+    NeedsPlus(Option<Span>),
+    NeedsColon,
+    HasColon,
+}
+
 pub(super) fn note_and_explain_region<'tcx>(
     tcx: TyCtxt<'tcx>,
     err: &mut Diag<'_>,

tests/ui/generics/missing-param-but-has-colon-144215.rs

@@ -0,0 +1,9 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/144215>
+
+#[rustfmt::skip]
+struct S<T:>(&'static T);
+//~^ ERROR the parameter type `T` may not live long enough
+//~| HELP consider adding an explicit lifetime bound
+//~| SUGGESTION  'static
+
+fn main() {}

tests/ui/generics/missing-param-but-has-colon-144215.stderr

@@ -0,0 +1,17 @@
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/missing-param-but-has-colon-144215.rs:4:14
+   |
+LL | struct S<T:>(&'static T);
+   |              ^^^^^^^^^^
+   |              |
+   |              the parameter type `T` must be valid for the static lifetime...
+   |              ...so that the reference type `&'static T` does not outlive the data it points at
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL | struct S<T: 'static>(&'static T);
+   |             +++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0310`.