minor cleanup

Author: jyn514

src/cargo/core/compiler/custom_build.rs

@@ -269,12 +269,7 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
             }
         })
         .collect::<Vec<_>>();
-    let library_name = unit
-        .pkg
-        .targets()
-        .iter()
-        .find(|t| t.is_lib())
-        .map(|t| t.crate_name());
+    let library_name = unit.pkg.library().map(|t| t.crate_name());
     let pkg_descr = unit.pkg.to_string();
     let build_script_outputs = Arc::clone(&cx.build_script_outputs);
     let id = unit.pkg.package_id();
@@ -881,11 +876,7 @@ fn prev_build_output(cx: &mut Context<'_, '_>, unit: &Unit) -> (Option<BuildOutp
     (
         BuildOutput::parse_file(
             &output_file,
-            unit.pkg
-                .targets()
-                .iter()
-                .find(|t| t.is_lib())
-                .map(|t| t.crate_name()),
+            unit.pkg.library().map(|t| t.crate_name()),
             &unit.pkg.to_string(),
             &prev_script_out_dir,
             &script_out_dir,

src/cargo/core/package.rs

@@ -151,6 +151,10 @@ impl Package {
     pub fn targets(&self) -> &[Target] {
         self.manifest().targets()
     }
+    /// Gets the library crate for this package, if it exists.
+    pub fn library(&self) -> Option<&Target> {
+        self.targets().iter().find(|t| t.is_lib())
+    }
     /// Gets the current package version.
     pub fn version(&self) -> &Version {
         self.package_id().version()