refactor: use Cow to avoid unnecessary allocations

src/cargo/core/source_id.rs

@@ -7,6 +7,7 @@ use crate::util::{config, CanonicalUrl, CargoResult, Config, IntoUrl, ToSemver};
 use anyhow::Context;
 use serde::de;
 use serde::ser;
+use std::borrow::Cow;
 use std::cmp::{self, Ordering};
 use std::collections::HashSet;
 use std::fmt::{self, Formatter};
@@ -308,17 +309,17 @@ impl SourceId {
     }
 
     /// Displays the name of a registry if it has one. Otherwise just the URL.
-    pub fn display_registry_name(self) -> String {
+    pub fn display_registry_name<'a>(self) -> Cow<'a, str> {
         if self.is_crates_io() {
-            CRATES_IO_REGISTRY.to_string()
+            CRATES_IO_REGISTRY.into()
         } else if let Some(key) = &self.inner.registry_key {
-            key.clone()
+            key.into()
         } else if self.precise().is_some() {
             // We remove `precise` here to retrieve an permissive version of
             // `SourceIdInner`, which may contain the registry name.
             self.with_precise(None).display_registry_name()
         } else {
-            url_display(self.url())
+            url_display(self.url()).into()
         }
     }
 

src/cargo/ops/mod.rs

@@ -75,7 +75,7 @@ fn check_dep_has_version(dep: &crate::core::Dependency, publish: bool) -> crate:
 
     if !dep.specified_req() && dep.is_transitive() {
         let dep_version_source = dep.registry_id().map_or_else(
-            || CRATES_IO_DOMAIN.to_string(),
+            || CRATES_IO_DOMAIN.into(),
             |registry_id| registry_id.display_registry_name(),
         );
         anyhow::bail!(