cli: parse --color option and reconfigure ui

I often redirect the jj output to pager, so I set ui.color = "always" in
config file. This patch allows me to remove such config, and instead specify
--color=always only when needed.

CHANGELOG.md

@@ -109,6 +109,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * The "(no name/email configured)" placeholder value for name/email will now be
   replaced if once you modify a commit after having configured your name/email.
 
+* Color setting can now be overridden by `--color=always|never|auto` option.
+
 ### Fixed bugs
 
 * When rebasing a conflict where one side modified a file and the other side

src/commands.rs

@@ -74,7 +74,7 @@ use crate::graphlog::{AsciiGraphDrawer, Edge};
 use crate::template_parser::TemplateParser;
 use crate::templater::Template;
 use crate::ui;
-use crate::ui::{FilePathParseError, Ui};
+use crate::ui::{ColorChoice, FilePathParseError, Ui};
 
 pub enum CommandError {
     UserError(String),
@@ -1101,6 +1101,14 @@ struct GlobalArgs {
         default_value = "@"
     )]
     at_operation: String,
+    /// When to colorize output (always, never, auto)
+    #[clap(
+        long,
+        value_name = "WHEN",
+        global = true,
+        help_heading = "GLOBAL OPTIONS"
+    )]
+    color: Option<ColorChoice>,
 }
 
 #[derive(Subcommand, Clone, Debug)]
@@ -5207,6 +5215,10 @@ where
     }
 
     let args = parse_args(ui.settings(), &string_args)?;
+    if let Some(choice) = args.global_args.color {
+        // Here we assume ui was created for_terminal().
+        ui.reset_color_for_terminal(choice);
+    }
     let app = Args::command();
     let command_helper = CommandHelper::new(app, string_args, args.global_args.clone());
     match &args.command {

tests/test_global_opts.rs

@@ -95,20 +95,34 @@ fn test_repo_arg_with_git_clone() {
 fn test_color_config() {
     let mut test_env = TestEnvironment::default();
 
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    // Test that --color=always is respected.
+    let stdout = test_env.jj_cmd_success(&repo_path, &["--color=always", "log", "-T", "commit_id"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o 0000000000000000000000000000000000000000
+    "###);
+
     // Test that color is used if it's requested in the config file
     test_env.add_config(
         br#"[ui]
 color="always""#,
     );
-    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
-
-    let repo_path = test_env.env_root().join("repo");
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "commit_id"]);
     insta::assert_snapshot!(stdout, @r###"
     @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     o 0000000000000000000000000000000000000000
     "###);
 
+    // Test that --color=never overrides the config.
+    let stdout = test_env.jj_cmd_success(&repo_path, &["--color=never", "log", "-T", "commit_id"]);
+    insta::assert_snapshot!(stdout, @r###"
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o 0000000000000000000000000000000000000000
+    "###);
+
     // Test that NO_COLOR does NOT override the request for color in the config file
     test_env.add_env_var("NO_COLOR", "");
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "commit_id"]);
@@ -148,6 +162,7 @@ fn test_help() {
 
     GLOBAL OPTIONS:
             --at-operation <AT_OPERATION>    Operation to load the repo at [default: @] [aliases: at-op]
+            --color <WHEN>                   When to colorize output (always, never, auto)
         -h, --help                           Print help information, more help with --help than with -h
             --no-commit-working-copy         Don't commit the working copy
         -R, --repository <REPOSITORY>        Path to repository to operate on