feat(trim-paths): set env CARGO_TRIM_PATHS for build scripts

src/cargo/core/compiler/custom_build.rs

@@ -307,6 +307,10 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
         cmd.env("CARGO_MANIFEST_LINKS", links);
     }
 
+    if let Some(trim_paths) = unit.profile.trim_paths.as_ref() {
+        cmd.env("CARGO_TRIM_PATHS", trim_paths.to_string());
+    }
+
     // Be sure to pass along all enabled features for this package, this is the
     // last piece of statically known information that we have.
     for feat in &unit.features {

src/cargo/core/profiles.rs

@@ -327,6 +327,7 @@ impl Profiles {
         result.root = for_unit_profile.root;
         result.debuginfo = for_unit_profile.debuginfo;
         result.opt_level = for_unit_profile.opt_level;
+        result.trim_paths = for_unit_profile.trim_paths.clone();
         result
     }
 

tests/testsuite/profile_trim_paths.rs

@@ -511,3 +511,69 @@ fn object_works() {
     assert!(memchr::memmem::find(&stdout, registry_src_bytes).is_none());
     assert!(memchr::memmem::find(&stdout, pkg_root).is_none());
 }
+
+// TODO: might want to move to test/testsuite/build_script.rs once stabilized.
+#[cargo_test(nightly, reason = "-Zremap-path-scope is unstable")]
+fn custom_build_env_var_trim_paths() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+           "#,
+        )
+        .file("src/lib.rs", "")
+        .file("build.rs", "")
+        .build();
+
+    let test_cases = [
+        ("[]", "none"),
+        ("\"all\"", "all"),
+        ("\"diagnostics\"", "diagnostics"),
+        ("\"macro\"", "macro"),
+        ("\"none\"", "none"),
+        ("\"object\"", "object"),
+        ("false", "none"),
+        ("true", "all"),
+        (
+            r#"["diagnostics", "macro", "object"]"#,
+            "diagnostics,macro,object",
+        ),
+    ];
+
+    for (opts, expected) in test_cases {
+        p.change_file(
+            "Cargo.toml",
+            &format!(
+                r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+
+                [profile.dev]
+                trim-paths = {opts}
+                "#
+            ),
+        );
+
+        p.change_file(
+            "build.rs",
+            &format!(
+                r#"
+                fn main() {{
+                    assert_eq!(
+                        std::env::var("CARGO_TRIM_PATHS").unwrap().as_str(),
+                        "{expected}",
+                    );
+                }}
+                "#
+            ),
+        );
+
+        p.cargo("build -Ztrim-paths")
+            .masquerade_as_nightly_cargo(&["-Ztrim-paths"])
+            .run();
+    }
+}