Speed up path searching with `find_library_crate`.

By doing prefix and suffix checking on a `String` copy of each relevant
`PathBuf`, rather than the `PathBuf` itself.

src/librustc_metadata/locator.rs

@@ -543,8 +543,8 @@ impl<'a> CrateLocator<'a> {
         // of the crate id (path/name/id).
         //
         // The goal of this step is to look at as little metadata as possible.
-        self.filesearch.search(|path, kind| {
-            let file = match path.file_name().and_then(|s| s.to_str()) {
+        self.filesearch.search(|spf, kind| {
+            let file = match &spf.file_name_str {
                 None => return FileDoesntMatch,
                 Some(file) => file,
             };
@@ -556,20 +556,18 @@ impl<'a> CrateLocator<'a> {
                 (&file[(dylib_prefix.len())..(file.len() - dypair.1.len())], CrateFlavor::Dylib)
             } else {
                 if file.starts_with(&staticlib_prefix) && file.ends_with(&staticpair.1) {
-                    staticlibs.push(CrateMismatch {
-                        path: path.to_path_buf(),
-                        got: "static".to_string(),
-                    });
+                    staticlibs
+                        .push(CrateMismatch { path: spf.path.clone(), got: "static".to_string() });
                 }
                 return FileDoesntMatch;
             };
 
-            info!("lib candidate: {}", path.display());
+            info!("lib candidate: {}", spf.path.display());
 
             let hash_str = hash.to_string();
             let slot = candidates.entry(hash_str).or_default();
             let (ref mut rlibs, ref mut rmetas, ref mut dylibs) = *slot;
-            fs::canonicalize(path)
+            fs::canonicalize(&spf.path)
                 .map(|p| {
                     if seen_paths.contains(&p) {
                         return FileDoesntMatch;

src/librustc_session/filesearch.rs

@@ -7,7 +7,7 @@ use std::env;
 use std::fs;
 use std::path::{Path, PathBuf};
 
-use crate::search_paths::{PathKind, SearchPath};
+use crate::search_paths::{PathKind, SearchPath, SearchPathFile};
 use log::debug;
 use rustc_fs_util::fix_windows_verbatim_for_gcc;
 
@@ -43,28 +43,28 @@ impl<'a> FileSearch<'a> {
 
     pub fn search<F>(&self, mut pick: F)
     where
-        F: FnMut(&Path, PathKind) -> FileMatch,
+        F: FnMut(&SearchPathFile, PathKind) -> FileMatch,
     {
         for search_path in self.search_paths() {
             debug!("searching {}", search_path.dir.display());
-            fn is_rlib(p: &Path) -> bool {
-                p.extension() == Some("rlib".as_ref())
+            fn is_rlib(spf: &SearchPathFile) -> bool {
+                if let Some(f) = &spf.file_name_str { f.ends_with(".rlib") } else { false }
             }
             // Reading metadata out of rlibs is faster, and if we find both
             // an rlib and a dylib we only read one of the files of
             // metadata, so in the name of speed, bring all rlib files to
             // the front of the search list.
-            let files1 = search_path.files.iter().filter(|p| is_rlib(p));
-            let files2 = search_path.files.iter().filter(|p| !is_rlib(p));
-            for path in files1.chain(files2) {
-                debug!("testing {}", path.display());
-                let maybe_picked = pick(path, search_path.kind);
+            let files1 = search_path.files.iter().filter(|spf| is_rlib(&spf));
+            let files2 = search_path.files.iter().filter(|spf| !is_rlib(&spf));
+            for spf in files1.chain(files2) {
+                debug!("testing {}", spf.path.display());
+                let maybe_picked = pick(spf, search_path.kind);
                 match maybe_picked {
                     FileMatches => {
-                        debug!("picked {}", path.display());
+                        debug!("picked {}", spf.path.display());
                     }
                     FileDoesntMatch => {
-                        debug!("rejected {}", path.display());
+                        debug!("rejected {}", spf.path.display());
                     }
                 }
             }

src/librustc_session/search_paths.rs

@@ -6,7 +6,31 @@ use std::path::{Path, PathBuf};
 pub struct SearchPath {
     pub kind: PathKind,
     pub dir: PathBuf,
-    pub files: Vec<PathBuf>,
+    pub files: Vec<SearchPathFile>,
+}
+
+// The obvious implementation of `SearchPath::files` is a `Vec<PathBuf>`. But
+// it is searched repeatedly by `find_library_crate`, and the searches involve
+// checking the prefix and suffix of the filename of each `PathBuf`. This is
+// doable, but very slow, because it involves calls to `file_name` and
+// `extension` that are themselves slow.
+//
+// This type augments the `PathBuf` with an `Option<String>` containing the
+// `PathBuf`'s filename. The prefix and suffix checking is much faster on the
+// `Option<String>` than the `PathBuf`. (It's an `Option` because
+// `Path::file_name` can fail; if that happens then all subsequent checking
+// will also fail, which is fine.)
+#[derive(Clone, Debug)]
+pub struct SearchPathFile {
+    pub path: PathBuf,
+    pub file_name_str: Option<String>,
+}
+
+impl SearchPathFile {
+    fn new(path: PathBuf) -> SearchPathFile {
+        let file_name_str = path.file_name().and_then(|f| f.to_str()).map(|s| s.to_string());
+        SearchPathFile { path, file_name_str }
+    }
 }
 
 #[derive(PartialEq, Clone, Copy, Debug, Hash, Eq, RustcEncodable, RustcDecodable)]
@@ -60,7 +84,9 @@ impl SearchPath {
     fn new(kind: PathKind, dir: PathBuf) -> Self {
         // Get the files within the directory.
         let files = match std::fs::read_dir(&dir) {
-            Ok(files) => files.filter_map(|p| p.ok().map(|s| s.path())).collect::<Vec<_>>(),
+            Ok(files) => files
+                .filter_map(|e| e.ok().map(|e| SearchPathFile::new(e.path())))
+                .collect::<Vec<_>>(),
             Err(..) => vec![],
         };