Don't read "installation" config from GIT_CONFIG

gix-path/src/env/git/mod.rs

@@ -140,8 +140,11 @@ fn git_cmd(executable: PathBuf) -> Command {
     // scope. Although `GIT_CONFIG_NOSYSTEM` will suppress this as well, passing --system omits it.
     cmd.args(["config", "-lz", "--show-origin", "--name-only"])
         .current_dir(cwd)
-        .env_remove("GIT_COMMON_DIR") // We are setting `GIT_DIR`.
+        .env_remove("GIT_CONFIG")
         .env_remove("GIT_DISCOVERY_ACROSS_FILESYSTEM")
+        .env_remove("GIT_OBJECT_DIRECTORY")
+        .env_remove("GIT_ALTERNATE_OBJECT_DIRECTORIES")
+        .env_remove("GIT_COMMON_DIR")
         .env("GIT_DIR", NULL_DEVICE) // Avoid getting local-scope config.
         .env("GIT_WORK_TREE", NULL_DEVICE) // Avoid confusion when debugging.
         .stdin(Stdio::null())

gix-path/src/env/git/tests.rs

@@ -453,6 +453,13 @@ mod exe_info {
         check_exe_info();
     }
 
+    #[test]
+    #[serial]
+    fn tolerates_git_config_env_var() {
+        let _env = gix_testtools::Env::new().set("GIT_CONFIG", NULL_DEVICE);
+        check_exe_info();
+    }
+
     #[test]
     #[serial]
     fn same_result_with_broken_temp() {
@@ -480,6 +487,19 @@ mod exe_info {
         assert_eq!(with_unmodified_env, with_oversanitized_env);
     }
 
+    #[test]
+    #[serial]
+    fn same_result_with_git_config_env_var() {
+        let with_unmodified_env = exe_info();
+
+        let with_git_config_env_var = {
+            let _env = gix_testtools::Env::new().set("GIT_CONFIG", NULL_DEVICE);
+            exe_info()
+        };
+
+        assert_eq!(with_unmodified_env, with_git_config_env_var);
+    }
+
     #[test]
     #[serial]
     #[cfg(not(target_os = "macos"))] // Assumes no higher "unknown" scope. The `nosystem` case works.
@@ -556,6 +576,33 @@ mod exe_info {
         );
     }
 
+    #[test]
+    #[serial]
+    fn never_from_git_config_env_var() {
+        let repo = gix_testtools::scripted_fixture_read_only("local_config.sh").expect("script succeeds");
+
+        // Get an absolute path to a config file that is non-UNC if possible so any Git accepts it.
+        let config_path = std::env::current_dir()
+            .expect("got CWD")
+            .join(repo)
+            .join(".git")
+            .join("config")
+            .to_str()
+            .expect("valid UTF-8")
+            .to_owned();
+
+        let _env = gix_testtools::Env::new()
+            .set("GIT_CONFIG_NOSYSTEM", "1")
+            .set("GIT_CONFIG_GLOBAL", NULL_DEVICE)
+            .set("GIT_CONFIG", config_path);
+
+        let maybe_path = exe_info();
+        assert_eq!(
+            maybe_path, None,
+            "Should find no config path from GIT_CONFIG (even if nonempty)"
+        );
+    }
+
     #[test]
     fn first_file_from_config_with_origin() {
         let macos =