Try to avoid string copies

Author: bugadani

src/librustdoc/config.rs

@@ -474,7 +474,7 @@ impl Options {
         };
 
         let mut id_map = html::markdown::IdMap::new();
-        id_map.populate(html::render::initial_ids());
+        id_map.populate(&html::render::INITIAL_IDS);
         let external_html = match ExternalHtml::load(
             &matches.opt_strs("html-in-header"),
             &matches.opt_strs("html-before-content"),

src/librustdoc/html/markdown.rs

@@ -1332,7 +1332,7 @@ impl IdMap {
         IdMap { map: init_id_map() }
     }
 
-    crate fn populate<I: IntoIterator<Item = String>>(&mut self, ids: I) {
+    crate fn populate<I: IntoIterator<Item = S>, S: AsRef<str> + ToString>(&mut self, ids: I) {
         for id in ids {
             let _ = self.derive(id);
         }
@@ -1342,11 +1342,11 @@ impl IdMap {
         self.map = init_id_map();
     }
 
-    crate fn derive(&mut self, candidate: String) -> String {
-        let id = match self.map.get_mut(&candidate) {
-            None => candidate,
+    crate fn derive<S: AsRef<str> + ToString>(&mut self, candidate: S) -> String {
+        let id = match self.map.get_mut(candidate.as_ref()) {
+            None => candidate.to_string(),
             Some(a) => {
-                let id = format!("{}-{}", candidate, *a);
+                let id = format!("{}-{}", candidate.as_ref(), *a);
                 *a += 1;
                 id
             }

src/librustdoc/html/render/mod.rs

@@ -359,28 +359,24 @@ crate struct StylePath {
 
 thread_local!(crate static CURRENT_DEPTH: Cell<usize> = Cell::new(0));
 
-crate fn initial_ids() -> Vec<String> {
-    [
-        "main",
-        "search",
-        "help",
-        "TOC",
-        "render-detail",
-        "associated-types",
-        "associated-const",
-        "required-methods",
-        "provided-methods",
-        "implementors",
-        "synthetic-implementors",
-        "implementors-list",
-        "synthetic-implementors-list",
-        "methods",
-        "implementations",
-    ]
-    .iter()
-    .map(|id| (String::from(*id)))
-    .collect()
-}
+// FIXME: make this work
+crate const INITIAL_IDS: [&'static str; 15] = [
+    "main",
+    "search",
+    "help",
+    "TOC",
+    "render-detail",
+    "associated-types",
+    "associated-const",
+    "required-methods",
+    "provided-methods",
+    "implementors",
+    "synthetic-implementors",
+    "implementors-list",
+    "synthetic-implementors-list",
+    "methods",
+    "implementations",
+];
 
 /// Generates the documentation for `crate` into the directory `dst`
 impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
@@ -1581,7 +1577,7 @@ impl Context<'_> {
 
         {
             self.id_map.borrow_mut().reset();
-            self.id_map.borrow_mut().populate(initial_ids());
+            self.id_map.borrow_mut().populate(&INITIAL_IDS);
         }
 
         if !self.render_redirect_pages {