made some fixes

Author: Kivooeo

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -2764,7 +2764,7 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
                     let (msg, sugg) = match source {
                         PathSource::Type | PathSource::PreciseCapturingArg(TypeNS) => {
-                            ("you might be missing a type parameter", ident)
+                            ("you might be missing a type parameter", ident.clone())
                         }
                         PathSource::Expr(_) | PathSource::PreciseCapturingArg(ValueNS) => (
                             "you might be missing a const parameter",
@@ -2786,16 +2786,15 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                         "Item", "Output", "Error", "Target", "Value", "Args",
                         "Res", "Ret", "This", "Iter", "Type",
                     ];
-                    let is_common_generic = common_generic_names.contains(&sugg.as_str());
-                    let looks_like_camel_case = sugg
+                    let is_common_generic = common_generic_names.contains(&&*ident);
+                    let looks_like_camel_case = ident 
                         .chars()
                         .next()
-                        .map(|c| c.is_uppercase())
-                        .unwrap_or(false)
-                        && sugg.chars().skip(1).any(|c| c.is_lowercase());
+                        .is_some_and(|c| c.is_uppercase())
+                        && ident.chars().skip(1).any(|c| c.is_lowercase());
 
                     // If it's not a known generic name and looks like a concrete type, skip the suggestion.
-                    if !is_common_generic && looks_like_camel_case && sugg.len() > 3 {
+                    if !is_common_generic && looks_like_camel_case && ident.len() > 3 {
                         return None;
                     }
                     let (span, sugg) = if let [.., param] = &generics.params[..] {

tests/ui/traits/missing-type-param-suggestion-issue-139999.rs

@@ -3,4 +3,20 @@ fn do_something() -> Option<ForgotToImport> {
     None
 }
 
+fn do_something_T() -> Option<T> {
+    //~^ cannot find type `T` in this scope [E0412]
+    None
+}
+
+fn do_something_Type() -> Option<Type> {
+    //~^ cannot find type `Type` in this scope [E0412]
+    None
+}
+
+fn do_something_const() -> [(); N] {
+    //~^ cannot find value `N` in this scope [E0425]
+    [(); N]
+    //~^ cannot find value `N` in this scope [E0425]
+}
+
 fn main() {}

tests/ui/traits/missing-type-param-suggestion-issue-139999.stderr

@@ -4,6 +4,51 @@ error[E0412]: cannot find type `ForgotToImport` in this scope
 LL | fn do_something() -> Option<ForgotToImport> {
    |                             ^^^^^^^^^^^^^^ not found in this scope
 
-error: aborting due to 1 previous error
+error[E0412]: cannot find type `T` in this scope
+  --> $DIR/missing-type-param-suggestion-issue-139999.rs:6:31
+   |
+LL | fn do_something_T() -> Option<T> {
+   |                               ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | fn do_something_T<T>() -> Option<T> {
+   |                  +++
+
+error[E0412]: cannot find type `Type` in this scope
+  --> $DIR/missing-type-param-suggestion-issue-139999.rs:11:34
+   |
+LL | fn do_something_Type() -> Option<Type> {
+   |                                  ^^^^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | fn do_something_Type<Type>() -> Option<Type> {
+   |                     ++++++
+
+error[E0425]: cannot find value `N` in this scope
+  --> $DIR/missing-type-param-suggestion-issue-139999.rs:16:33
+   |
+LL | fn do_something_const() -> [(); N] {
+   |                                 ^ not found in this scope
+   |
+help: you might be missing a const parameter
+   |
+LL | fn do_something_const<const N: /* Type */>() -> [(); N] {
+   |                      +++++++++++++++++++++
+
+error[E0425]: cannot find value `N` in this scope
+  --> $DIR/missing-type-param-suggestion-issue-139999.rs:18:10
+   |
+LL |     [(); N]
+   |          ^ not found in this scope
+   |
+help: you might be missing a const parameter
+   |
+LL | fn do_something_const<const N: /* Type */>() -> [(); N] {
+   |                      +++++++++++++++++++++
+
+error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0412`.
+Some errors have detailed explanations: E0412, E0425.
+For more information about an error, try `rustc --explain E0412`.