refactor: clean up clippy::perf lint warnings (#15631)

### What does this PR try to resolve?

The `clippy::perf` lint group is fairly useful for catching bad
practices that might hurt performance marginally.

This PR fixes most of them except `clippy::large_enum_variant`, which
doesn't feel right at this moment and need more researches. And that is
why I didn't enable the lint group.

### How to test and review this PR?

crates/cargo-test-support/src/paths.rs

@@ -66,7 +66,7 @@ pub fn global_root() -> PathBuf {
 // [*] It does set the thread name, but only when running concurrently. If not
 // running concurrently, all tests are run on the main thread.
 thread_local! {
-    static TEST_ID: RefCell<Option<usize>> = RefCell::new(None);
+    static TEST_ID: RefCell<Option<usize>> = const { RefCell::new(None) };
 }
 
 /// See [`init_root`]

crates/cargo-test-support/src/publish.rs

@@ -322,7 +322,7 @@ fn split_index_features(mut features: FeatureMap) -> (FeatureMap, Option<Feature
             .iter()
             .any(|value| value.starts_with("dep:") || value.contains("?/"))
         {
-            let new_values = values.drain(..).collect();
+            let new_values = std::mem::take(values);
             features2.insert(feat.clone(), new_values);
         }
     }

crates/cargo-test-support/src/registry.rs

@@ -646,15 +646,15 @@ pub struct HttpServerHandle {
 
 impl HttpServerHandle {
     pub fn index_url(&self) -> Url {
-        Url::parse(&format!("sparse+http://{}/index/", self.addr.to_string())).unwrap()
+        Url::parse(&format!("sparse+http://{}/index/", self.addr)).unwrap()
     }
 
     pub fn api_url(&self) -> Url {
-        Url::parse(&format!("http://{}/", self.addr.to_string())).unwrap()
+        Url::parse(&format!("http://{}/", self.addr)).unwrap()
     }
 
     pub fn dl_url(&self) -> Url {
-        Url::parse(&format!("http://{}/dl", self.addr.to_string())).unwrap()
+        Url::parse(&format!("http://{}/dl", self.addr)).unwrap()
     }
 
     fn stop(&self) {
@@ -892,7 +892,7 @@ impl HttpServer {
 
         // - The URL matches the registry base URL
         if footer.url != "https://github.com/rust-lang/crates.io-index"
-            && footer.url != &format!("sparse+http://{}/index/", self.addr.to_string())
+            && footer.url != &format!("sparse+http://{}/index/", self.addr)
         {
             return false;
         }

crates/mdman/src/format/man.rs

@@ -427,6 +427,7 @@ impl<'e> ManRenderer<'e> {
     }
 }
 
+#[allow(clippy::collapsible_str_replace)]
 fn escape(s: &str) -> Result<String, Error> {
     // Note: Possible source on output escape sequences: https://man7.org/linux/man-pages/man7/groff_char.7.html.
     //       Otherwise, use generic escaping in the form `\[u1EE7]` or `\[u1F994]`.

crates/resolver-tests/tests/proptests.rs

@@ -205,9 +205,7 @@ proptest! {
                     // If resolution was successful, then unpublishing a version of a crate
                     // that was not selected should not change that.
                     let not_selected: Vec<_> = input
-                        .iter()
-                        .cloned()
-                        .filter(|x| !r.contains(&x.package_id()))
+                        .iter().filter(|&x| !r.contains(&x.package_id())).cloned()
                         .collect();
 
                     if !not_selected.is_empty() {
@@ -215,9 +213,7 @@ proptest! {
 
                         let new_reg = registry(
                             input
-                                .iter()
-                                .cloned()
-                                .filter(|x| !indexes_to_unpublish.contains(&x))
+                                .iter().filter(|&x| !indexes_to_unpublish.contains(&x)).cloned()
                                 .collect(),
                         );
 
@@ -248,9 +244,7 @@ proptest! {
 
                     let new_reg = registry(
                         input
-                            .iter()
-                            .cloned()
-                            .filter(|x| !indexes_to_unpublish.contains(&x))
+                            .iter().filter(|&x| !indexes_to_unpublish.contains(&x)).cloned()
                             .collect(),
                     );
 

crates/resolver-tests/tests/resolve.rs

@@ -741,8 +741,8 @@ fn incomplete_information_skipping() {
     let new_reg = registry(
         input
             .iter()
+            .filter(|&x| package_to_yank != x.package_id())
             .cloned()
-            .filter(|x| package_to_yank != x.package_id())
             .collect(),
     );
     assert_eq!(input.len(), new_reg.len() + 1);
@@ -810,8 +810,8 @@ fn incomplete_information_skipping_2() {
     let new_reg = registry(
         input
             .iter()
+            .filter(|&x| package_to_yank != x.package_id())
             .cloned()
-            .filter(|x| package_to_yank != x.package_id())
             .collect(),
     );
     assert_eq!(input.len(), new_reg.len() + 1);
@@ -860,8 +860,8 @@ fn incomplete_information_skipping_3() {
     let new_reg = registry(
         input
             .iter()
+            .filter(|&x| package_to_yank != x.package_id())
             .cloned()
-            .filter(|x| package_to_yank != x.package_id())
             .collect(),
     );
     assert_eq!(input.len(), new_reg.len() + 1);

src/cargo/core/features.rs

@@ -975,7 +975,7 @@ impl GitFeatures {
     }
 
     fn expecting() -> String {
-        let fields = vec!["`shallow-index`", "`shallow-deps`"];
+        let fields = ["`shallow-index`", "`shallow-deps`"];
         format!(
             "unstable 'git' only takes {} as valid inputs",
             fields.join(" and ")
@@ -1087,7 +1087,7 @@ impl GitoxideFeatures {
     }
 
     fn expecting() -> String {
-        let fields = vec!["`fetch`", "`checkout`", "`internal-use-git2`"];
+        let fields = ["`fetch`", "`checkout`", "`internal-use-git2`"];
         format!(
             "unstable 'gitoxide' only takes {} as valid inputs, for shallow fetches see `-Zgit=shallow-index,shallow-deps`",
             fields.join(" and ")

src/cargo/core/manifest.rs

@@ -151,7 +151,7 @@ impl ManifestMetadata {
     /// Whether the given env var should be tracked by Cargo's dep-info.
     pub fn should_track(env_key: &str) -> bool {
         let keys = MetadataEnvs::keys();
-        keys.iter().any(|k| *k == env_key)
+        keys.contains(&env_key)
     }
 
     pub fn env_var<'a>(&'a self, env_key: &str) -> Option<Cow<'a, str>> {
@@ -1016,21 +1016,21 @@ impl Target {
 
     pub fn is_dylib(&self) -> bool {
         match self.kind() {
-            TargetKind::Lib(libs) => libs.iter().any(|l| *l == CrateType::Dylib),
+            TargetKind::Lib(libs) => libs.contains(&CrateType::Dylib),
             _ => false,
         }
     }
 
     pub fn is_cdylib(&self) -> bool {
         match self.kind() {
-            TargetKind::Lib(libs) => libs.iter().any(|l| *l == CrateType::Cdylib),
+            TargetKind::Lib(libs) => libs.contains(&CrateType::Cdylib),
             _ => false,
         }
     }
 
     pub fn is_staticlib(&self) -> bool {
         match self.kind() {
-            TargetKind::Lib(libs) => libs.iter().any(|l| *l == CrateType::Staticlib),
+            TargetKind::Lib(libs) => libs.contains(&CrateType::Staticlib),
             _ => false,
         }
     }

src/cargo/core/package.rs

@@ -1182,7 +1182,7 @@ mod tls {
 
     use super::Downloads;
 
-    thread_local!(static PTR: Cell<usize> = Cell::new(0));
+    thread_local!(static PTR: Cell<usize> = const { Cell::new(0) });
 
     pub(crate) fn with<R>(f: impl FnOnce(Option<&Downloads<'_, '_>>) -> R) -> R {
         let ptr = PTR.with(|p| p.get());

src/cargo/core/resolver/encode.rs

@@ -698,7 +698,7 @@ impl ser::Serialize for Resolve {
                     None => "<none>",
                 };
                 let id = encodable_package_id(id, &state, self.version());
-                metadata.insert(format!("checksum {}", id.to_string()), checksum.to_string());
+                metadata.insert(format!("checksum {}", id), checksum.to_string());
             }
         }
 

src/cargo/ops/cargo_add/mod.rs

@@ -813,7 +813,7 @@ fn latest_compatible<'s>(
                 .unwrap_or(true)
         })
         .map(|(s, _)| s)
-        .last()
+        .next_back()
         .copied()
 }
 

src/cargo/ops/cargo_install.rs

@@ -202,10 +202,8 @@ impl<'gctx> InstallablePackage<'gctx> {
             // If we're installing in --locked mode and there's no `Cargo.lock` published
             // ie. the bin was published before https://github.com/rust-lang/cargo/pull/7026
             } else if !ws.root().join("Cargo.lock").exists() {
-                gctx.shell().warn(format!(
-                    "no Cargo.lock file published in {}",
-                    pkg.to_string()
-                ))?;
+                gctx.shell()
+                    .warn(format!("no Cargo.lock file published in {}", pkg))?;
             }
         }
         let pkg = if source_id.is_git() {

src/cargo/ops/cargo_test.rs

@@ -206,8 +206,7 @@ fn run_doc_tests(
         p.arg("--test");
 
         add_path_args(ws, unit, &mut p);
-        p.arg("--test-run-directory")
-            .arg(unit.pkg.root().to_path_buf());
+        p.arg("--test-run-directory").arg(unit.pkg.root());
 
         if let CompileKind::Target(target) = unit.kind {
             // use `rustc_target()` to properly handle JSON target paths

src/cargo/ops/cargo_update.rs

@@ -136,22 +136,19 @@ pub fn update_lockfile(ws: &Workspace<'_>, opts: &UpdateOptions<'_>) -> CargoRes
         // Mirror `--workspace` and never avoid workspace members.
         // Filtering them out here so the above processes them normally
         // so their dependencies can be updated as requested
-        to_avoid = to_avoid
-            .into_iter()
-            .filter(|id| {
-                for package in ws.members() {
-                    let member_id = package.package_id();
-                    // Skip checking the `version` because `previous_resolve` might have a stale
-                    // value.
-                    // When dealing with workspace members, the other fields should be a
-                    // sufficiently unique match.
-                    if id.name() == member_id.name() && id.source_id() == member_id.source_id() {
-                        return false;
-                    }
+        to_avoid.retain(|id| {
+            for package in ws.members() {
+                let member_id = package.package_id();
+                // Skip checking the `version` because `previous_resolve` might have a stale
+                // value.
+                // When dealing with workspace members, the other fields should be a
+                // sufficiently unique match.
+                if id.name() == member_id.name() && id.source_id() == member_id.source_id() {
+                    return false;
                 }
-                true
-            })
-            .collect();
+            }
+            true
+        });
 
         registry.add_sources(sources)?;
     }

src/cargo/ops/fix/mod.rs

@@ -546,7 +546,7 @@ fn check_resolver_change<'gctx>(
             }
             // Only trigger if updating the root package from 2018.
             let pkgs = opts.compile_opts.spec.get_packages(ws)?;
-            if !pkgs.iter().any(|&pkg| pkg == root_pkg) {
+            if !pkgs.contains(&root_pkg) {
                 // The root is not being migrated.
                 return Ok(());
             }

src/cargo/ops/registry/publish.rs

@@ -88,10 +88,7 @@ pub fn publish(ws: &Workspace<'_>, opts: &PublishOpts<'_>) -> CargoResult<()> {
     let mut pkgs = ws.members_with_features(&specs, &opts.cli_features)?;
     // In `members_with_features_old`, it will add "current" package (determined by the cwd)
     // So we need filter
-    pkgs = pkgs
-        .into_iter()
-        .filter(|(m, _)| specs.iter().any(|spec| spec.matches(m.package_id())))
-        .collect();
+    pkgs.retain(|(m, _)| specs.iter().any(|spec| spec.matches(m.package_id())));
 
     let (unpublishable, pkgs): (Vec<_>, Vec<_>) = pkgs
         .into_iter()

src/cargo/sources/git/utils.rs

@@ -1126,7 +1126,7 @@ fn fetch_with_gitoxide(
     let config_overrides = cargo_config_to_gitoxide_overrides(gctx)?;
     let repo_reinitialized = AtomicBool::default();
     let res = oxide::with_retry_and_progress(
-        &git2_repo.path().to_owned(),
+        git2_repo.path(),
         gctx,
         &|repo_path,
           should_interrupt,

src/cargo/sources/registry/download.rs

@@ -72,13 +72,7 @@ pub(super) fn download(
         && !url.contains(CHECKSUM_TEMPLATE)
     {
         // Original format before customizing the download URL was supported.
-        write!(
-            url,
-            "/{}/{}/download",
-            pkg.name(),
-            pkg.version().to_string()
-        )
-        .unwrap();
+        write!(url, "/{}/{}/download", pkg.name(), pkg.version()).unwrap();
     } else {
         let prefix = make_dep_path(&pkg.name(), true);
         url = url

src/cargo/sources/registry/http_remote.rs

@@ -869,7 +869,7 @@ mod tls {
     use super::Downloads;
     use std::cell::Cell;
 
-    thread_local!(static PTR: Cell<usize> = Cell::new(0));
+    thread_local!(static PTR: Cell<usize> = const { Cell::new(0) });
 
     pub(super) fn with<R>(f: impl FnOnce(Option<&Downloads<'_>>) -> R) -> R {
         let ptr = PTR.with(|p| p.get());

src/cargo/util/lints.rs

@@ -152,9 +152,9 @@ fn verify_feature_enabled(
                 &["workspace", "lints", "cargo", lint_name],
                 false,
             )
-            .expect(&format!(
-                "could not find `cargo::{lint_name}` in `[lints]`, or `[workspace.lints]` "
-            ));
+            .unwrap_or_else(|| {
+                panic!("could not find `cargo::{lint_name}` in `[lints]`, or `[workspace.lints]` ")
+            });
 
             let inherited_note = if let (Some(inherit_span_key), Some(inherit_span_value)) = (
                 get_span(manifest.document(), &["lints", "workspace"], false),
@@ -556,9 +556,9 @@ fn output_unknown_lints(
                 &["workspace", "lints", "cargo", lint_name],
                 false,
             )
-            .expect(&format!(
-                "could not find `cargo::{lint_name}` in `[lints]`, or `[workspace.lints]` "
-            ));
+            .unwrap_or_else(|| {
+                panic!("could not find `cargo::{lint_name}` in `[lints]`, or `[workspace.lints]` ")
+            });
 
             let inherited_note = if let (Some(inherit_span_key), Some(inherit_span_value)) = (
                 get_span(manifest.document(), &["lints", "workspace"], false),

src/cargo/util/rustc.rs

@@ -258,9 +258,7 @@ impl Cache {
         extra_fingerprint: u64,
     ) -> CargoResult<(String, String)> {
         let key = process_fingerprint(cmd, extra_fingerprint);
-        if self.data.outputs.contains_key(&key) {
-            debug!("rustc info cache hit");
-        } else {
+        if let std::collections::hash_map::Entry::Vacant(e) = self.data.outputs.entry(key) {
             debug!("rustc info cache miss");
             debug!("running {}", cmd);
             let output = cmd.output()?;
@@ -270,21 +268,20 @@ impl Cache {
             let stderr = String::from_utf8(output.stderr)
                 .map_err(|e| anyhow::anyhow!("{}: {:?}", e, e.as_bytes()))
                 .with_context(|| format!("`{}` didn't return utf8 output", cmd))?;
-            self.data.outputs.insert(
-                key,
-                Output {
-                    success: output.status.success(),
-                    status: if output.status.success() {
-                        String::new()
-                    } else {
-                        cargo_util::exit_status_to_string(output.status)
-                    },
-                    code: output.status.code(),
-                    stdout,
-                    stderr,
+            e.insert(Output {
+                success: output.status.success(),
+                status: if output.status.success() {
+                    String::new()
+                } else {
+                    cargo_util::exit_status_to_string(output.status)
                 },
-            );
+                code: output.status.code(),
+                stdout,
+                stderr,
+            });
             self.dirty = true;
+        } else {
+            debug!("rustc info cache hit");
         }
         let output = &self.data.outputs[&key];
         if output.success {

src/cargo/util/toml/mod.rs

@@ -1482,7 +1482,7 @@ pub fn to_real_manifest(
                 warnings.push(format!(
                     "file `{}` found to be present in multiple \
                  build targets:\n{}",
-                    target_path.display().to_string(),
+                    target_path.display(),
                     conflicts
                         .iter()
                         .map(|t| format!("  * `{}` target `{}`", t.kind().description(), t.name(),))
@@ -1986,7 +1986,7 @@ fn validate_dependencies(
             None => "dependencies",
         };
         let table_in_toml = if let Some(platform) = platform {
-            format!("target.{}.{kind_name}", platform.to_string())
+            format!("target.{platform}.{kind_name}")
         } else {
             kind_name.to_string()
         };

src/cargo/util/toml_mut/dependency.rs

@@ -1269,7 +1269,7 @@ mod tests {
             .unwrap();
             let dep = dep.set_source(WorkspaceSource::new());
             local
-                .insert_into_table(&vec![], &dep, &gctx, &crate_root, &Features::default())
+                .insert_into_table(&[], &dep, &gctx, &crate_root, &Features::default())
                 .unwrap();
             assert_eq!(local.data.to_string(), "dep.workspace = true\n");
         }

tests/testsuite/git.rs

@@ -1475,7 +1475,7 @@ fn dep_with_changed_submodule() {
     });
 
     let repo = git2::Repository::open(&git_project.root()).unwrap();
-    let mut sub = git::add_submodule(&repo, &git_project2.url().to_string(), Path::new("src"));
+    let mut sub = git::add_submodule(&repo, git_project2.url().as_ref(), Path::new("src"));
     git::commit(&repo);
 
     let p = project
@@ -1537,7 +1537,7 @@ project2
             .remote_add_fetch("origin", "refs/heads/*:refs/heads/*")
             .unwrap();
         subrepo
-            .remote_set_url("origin", &git_project3.url().to_string())
+            .remote_set_url("origin", git_project3.url().as_ref())
             .unwrap();
         let mut origin = subrepo.find_remote("origin").unwrap();
         origin.fetch(&Vec::<String>::new(), None, None).unwrap();

tests/testsuite/inheritable_workspace_fields.rs

@@ -466,7 +466,7 @@ fn inherit_own_detailed_dependencies() {
         .build();
 
     Package::new("dep", "0.1.2")
-        .feature("testing", &vec![])
+        .feature("testing", &[])
         .publish();
 
     p.cargo("check")

tests/testsuite/install.rs

@@ -766,7 +766,7 @@ fn multiple_crates_git_all() {
         )
         .build();
 
-    cargo_process(&format!("install --git {} bin1 bin2", p.url().to_string())).run();
+    cargo_process(&format!("install --git {} bin1 bin2", p.url())).run();
 }
 
 #[cargo_test]
@@ -2148,7 +2148,7 @@ fn git_install_reads_workspace_manifest() {
         )
         .build();
 
-    cargo_process(&format!("install --git {}", p.url().to_string()))
+    cargo_process(&format!("install --git {}", p.url()))
         .with_status(101)
         .with_stderr_data(str![[r#"
 [UPDATING] git repository `[ROOTURL]/foo`

tests/testsuite/package.rs

@@ -1457,7 +1457,7 @@ fn dirty_file_outside_pkg_root_inside_submodule() {
     });
     git::add_submodule(
         &repo,
-        &submodule.root().to_url().to_string(),
+        submodule.root().to_url().as_ref(),
         Path::new("submodule"),
     );
     p.symlink("submodule/file.txt", "isengard/src/file.txt");
@@ -3595,7 +3595,7 @@ fn larger_filesizes() {
                 description = "foo"
                 documentation = "https://example.com/"
             "#;
-    let lots_of_crabs = std::iter::repeat("🦀").take(1337).collect::<String>();
+    let lots_of_crabs = "🦀".repeat(1337);
     let main_rs_contents = format!(r#"fn main() {{ println!("{}"); }}"#, lots_of_crabs);
     let bar_txt_contents = "This file is relatively uncompressible, to increase the compressed
         package size beyond 1KiB.
@@ -3711,7 +3711,7 @@ fn symlink_filesizes() {
                 description = "foo"
                 homepage = "https://example.com/"
             "#;
-    let lots_of_crabs = std::iter::repeat("🦀").take(1337).collect::<String>();
+    let lots_of_crabs = "🦀".repeat(1337);
     let main_rs_contents = format!(r#"fn main() {{ println!("{}"); }}"#, lots_of_crabs);
     let bar_txt_contents = "This file is relatively uncompressible, to increase the compressed
         package size beyond 1KiB.

tests/testsuite/update.rs

@@ -1391,7 +1391,7 @@ fn update_precise_git_revisions() {
 
     // Now make a tag looks like an oid.
     // It requires a git fetch, as the oid cannot be found in preexisting git db.
-    let arbitrary_tag: String = std::iter::repeat('a').take(head_id.len()).collect();
+    let arbitrary_tag: String = "a".repeat(head_id.len());
     git::tag(&git_repo, &arbitrary_tag);
 
     p.cargo("update git --precise")