Rollup merge of #136736 - llogiq:small-resolve-refactor, r=jieyouxu

Small resolve refactor

I was looking into how resolve works in order to find a good way for clippy to shorten paths in messages and suggestions, and found a needless `.collect()` and a recursive function that could be written as a loop, also removed a panicky code path.

compiler/rustc_resolve/src/imports.rs

@@ -1500,7 +1500,7 @@ fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Sp
     let global = !names.is_empty() && names[0].name == kw::PathRoot;
     if let Some(pos) = pos {
         let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
-        names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
+        names_to_string(names.iter().map(|ident| ident.name))
     } else {
         let names = if global { &names[1..] } else { names };
         if names.is_empty() {
@@ -1508,7 +1508,7 @@ fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Sp
         } else {
             format!(
                 "{}::{}",
-                names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
+                names_to_string(names.iter().map(|ident| ident.name)),
                 import_kind_to_string(import_kind),
             )
         }

compiler/rustc_resolve/src/lib.rs

@@ -358,7 +358,7 @@ fn from_ident_and_id(ident: Ident, id: NodeId) -> Segment {
     }
 
     fn names_to_string(segments: &[Segment]) -> String {
-        names_to_string(&segments.iter().map(|seg| seg.ident.name).collect::<Vec<_>>())
+        names_to_string(segments.iter().map(|seg| seg.ident.name))
     }
 }
 
@@ -2241,13 +2241,13 @@ fn resolve_main(&mut self) {
     }
 }
 
-fn names_to_string(names: &[Symbol]) -> String {
+fn names_to_string(names: impl Iterator<Item = Symbol>) -> String {
     let mut result = String::new();
-    for (i, name) in names.iter().filter(|name| **name != kw::PathRoot).enumerate() {
+    for (i, name) in names.filter(|name| *name != kw::PathRoot).enumerate() {
         if i > 0 {
             result.push_str("::");
         }
-        if Ident::with_dummy_span(*name).is_raw_guess() {
+        if Ident::with_dummy_span(name).is_raw_guess() {
             result.push_str("r#");
         }
         result.push_str(name.as_str());
@@ -2256,31 +2256,32 @@ fn names_to_string(names: &[Symbol]) -> String {
 }
 
 fn path_names_to_string(path: &Path) -> String {
-    names_to_string(&path.segments.iter().map(|seg| seg.ident.name).collect::<Vec<_>>())
+    names_to_string(path.segments.iter().map(|seg| seg.ident.name))
 }
 
 /// A somewhat inefficient routine to obtain the name of a module.
-fn module_to_string(module: Module<'_>) -> Option<String> {
+fn module_to_string(mut module: Module<'_>) -> Option<String> {
     let mut names = Vec::new();
-
-    fn collect_mod(names: &mut Vec<Symbol>, module: Module<'_>) {
+    loop {
         if let ModuleKind::Def(.., name) = module.kind {
             if let Some(parent) = module.parent {
                 names.push(name);
-                collect_mod(names, parent);
+                module = parent
+            } else {
+                break;
             }
         } else {
             names.push(sym::opaque_module_name_placeholder);
-            collect_mod(names, module.parent.unwrap());
+            let Some(parent) = module.parent else {
+                return None;
+            };
+            module = parent;
         }
     }
-    collect_mod(&mut names, module);
-
     if names.is_empty() {
         return None;
     }
-    names.reverse();
-    Some(names_to_string(&names))
+    Some(names_to_string(names.iter().rev().copied()))
 }
 
 #[derive(Copy, Clone, Debug)]