cli: respect $NO_COLOR environment variable

CHANGELOG.md

@@ -21,6 +21,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   config file. That will then be read instead of your regular config file. This
   is mostly intended for testing and scripts.
 
+* The [standard `$NO_COLOR` environment variable](https://no-color.org/) is now
+  respected.
+
 ## [0.3.3] - 2022-03-16
 
 No changes, only trying to get the automated build to work.

src/ui.rs

@@ -46,6 +46,21 @@ fn new_formatter<'output>(
     }
 }
 
+fn use_color(settings: &UserSettings) -> bool {
+    if std::env::var("NO_COLOR").is_ok() {
+        return false;
+    }
+    let color_setting = settings
+        .config()
+        .get_string("ui.color")
+        .unwrap_or_else(|_| "auto".to_string());
+    match color_setting.as_str() {
+        "always" => true,
+        "never" => false,
+        _ => atty::is(Stream::Stdout),
+    }
+}
+
 impl<'stdout> Ui<'stdout> {
     pub fn new(
         cwd: PathBuf,
@@ -65,15 +80,7 @@ impl<'stdout> Ui<'stdout> {
     pub fn for_terminal(settings: UserSettings) -> Ui<'static> {
         let cwd = std::env::current_dir().unwrap();
         let stdout: Box<dyn Write + 'static> = Box::new(io::stdout());
-        let color_setting = settings
-            .config()
-            .get_string("ui.color")
-            .unwrap_or_else(|_| "auto".to_string());
-        let color = match color_setting.as_str() {
-            "always" => true,
-            "never" => false,
-            _ => atty::is(Stream::Stdout),
-        };
+        let color = use_color(&settings);
         Ui::new(cwd, stdout, color, settings)
     }
 

tests/test_global_opts.rs

@@ -85,6 +85,8 @@ fn test_repo_arg_with_git_clone() {
 #[test]
 fn test_color_config() {
     let test_env = TestEnvironment::default();
+
+    // Test that color is used if it's requested in the config file
     let mut config_file = std::fs::File::options()
         .append(true)
         .open(test_env.config_path())
@@ -110,4 +112,15 @@ color="always""#,
     @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     o 0000000000000000000000000000000000000000
     "###);
+
+    // Test that NO_COLOR overrides the request for color in the config file
+    let assert = test_env
+        .jj_cmd(&repo_path, &["log", "-T", "commit_id"])
+        .env("NO_COLOR", "")
+        .assert()
+        .success();
+    insta::assert_snapshot!(get_stdout_string(&assert), @r###"
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o 0000000000000000000000000000000000000000
+    "###);
 }