Omit system/global config in fixture scripts even amidst strange filenames

tests/tools/src/lib.rs

@@ -583,12 +583,16 @@ fn scripted_fixture_read_only_with_args_inner(
     Ok(script_result_directory)
 }
 
+#[cfg(windows)]
+const NULL_DEVICE: &str = "NUL";
+#[cfg(not(windows))]
+const NULL_DEVICE: &str = "/dev/null";
+
 fn configure_command<'a>(
     cmd: &'a mut std::process::Command,
     args: &[String],
     script_result_directory: &Path,
 ) -> &'a mut std::process::Command {
-    let never_path = if cfg!(windows) { "-" } else { ":" };
     let mut msys_for_git_bash_on_windows = std::env::var("MSYS").unwrap_or_default();
     msys_for_git_bash_on_windows.push_str(" winsymlinks:nativestrict");
     cmd.args(args)
@@ -599,8 +603,8 @@ fn configure_command<'a>(
         .env_remove("GIT_ASKPASS")
         .env_remove("SSH_ASKPASS")
         .env("MSYS", msys_for_git_bash_on_windows)
-        .env("GIT_CONFIG_SYSTEM", never_path)
-        .env("GIT_CONFIG_GLOBAL", never_path)
+        .env("GIT_CONFIG_SYSTEM", NULL_DEVICE)
+        .env("GIT_CONFIG_GLOBAL", NULL_DEVICE)
         .env("GIT_TERMINAL_PROMPT", "false")
         .env("GIT_AUTHOR_DATE", "2000-01-01 00:00:00 +0000")
         .env("GIT_AUTHOR_EMAIL", "[email protected]")
@@ -882,4 +886,55 @@ mod tests {
     fn parse_version_with_trailing_newline() {
         assert_eq!(git_version_from_bytes(b"git version 2.37.2\n").unwrap(), (2, 37, 2));
     }
+
+    const SCOPE_ENV_VALUE: &str = "gitconfig";
+
+    fn populate_ad_hoc_config_files(dir: &Path) {
+        const CONFIG_DATA: &[u8] = b"[foo]\n\tbar = baz\n";
+
+        let paths: &[PathBuf] = if cfg!(windows) {
+            let unc_literal_nul = dir.canonicalize().expect("directory exists").join("NUL");
+            &[dir.join(SCOPE_ENV_VALUE), dir.join("-"), unc_literal_nul]
+        } else {
+            &[dir.join(SCOPE_ENV_VALUE), dir.join("-"), dir.join(":")]
+        };
+
+        // Create the files.
+        for path in paths {
+            std::fs::write(path, CONFIG_DATA).expect("can write contents");
+        }
+
+        // Verify the files. This is mostly to show we really made a `\\?\...\NUL` on Windows.
+        for path in paths {
+            let buf = std::fs::read(path).expect("the file really exists");
+            assert_eq!(buf, CONFIG_DATA, "File {path:?} should be created");
+        }
+    }
+
+    fn check_configure_clears_scope(scope_env_key: &str, scope_option: &str) {
+        let temp = tempfile::TempDir::new().expect("can create temp dir");
+        let dir = temp.path();
+        populate_ad_hoc_config_files(dir);
+
+        let mut cmd = std::process::Command::new("git");
+        cmd.env(scope_env_key, SCOPE_ENV_VALUE); // configure_command() should override it.
+        let args = ["config", "-l", "--show-origin", scope_option].map(String::from);
+        configure_command(&mut cmd, &args, dir);
+
+        let output = cmd.output().expect("can run git");
+        let stdout = output.stdout.to_str().expect("valid UTF-8");
+        let status = output.status.code().expect("terminated normally");
+        assert_eq!(stdout, "", "should be no config variables to display");
+        assert_eq!(status, 0, "reading the config should nonetheless succeed");
+    }
+
+    #[test]
+    fn configure_command_clears_system_scope() {
+        check_configure_clears_scope("GIT_CONFIG_SYSTEM", "--system");
+    }
+
+    #[test]
+    fn configure_command_clears_global_scope() {
+        check_configure_clears_scope("GIT_CONFIG_GLOBAL", "--global");
+    }
 }