--list-languages should respect --color

Fixes #387

CHANGELOG.md

@@ -5,6 +5,11 @@
 Standalone `.` is now considered punctuation in the diff cost model,
 which improves diff results in some cases.
 
+### Command Line Interface
+
+`--list-languages` now respects the value of `--color`, whose default
+only uses styling when stdout is a TTY.
+
 ### Build
 
 Fixed an issue with building on Windows with gcc.

src/main.rs

@@ -132,9 +132,13 @@ fn main() {
                 }
             }
         }
-        Mode::ListLanguages => {
+        Mode::ListLanguages { use_color } => {
             for (language, extensions) in LANG_EXTENSIONS {
-                print!("{}", language_name(*language).bold());
+                let mut name = language_name(*language).to_string();
+                if use_color {
+                    name = name.bold().to_string();
+                }
+                print!("{}", name);
 
                 let mut extensions: Vec<&str> = (*extensions).into();
                 extensions.sort();

src/options.rs

@@ -196,7 +196,9 @@ pub enum Mode {
         /// The path that we should display for the RHS file.
         rhs_display_path: String,
     },
-    ListLanguages,
+    ListLanguages {
+        use_color: bool,
+    },
     DumpTreeSitter {
         path: String,
         language_override: Option<guess_language::Language>,
@@ -226,8 +228,22 @@ pub fn parse_args() -> Mode {
         None => None,
     };
 
+    let color_output = if let Some(color_when) = matches.value_of("color") {
+        if color_when == "always" {
+            ColorOutput::Always
+        } else if color_when == "never" {
+            ColorOutput::Never
+        } else {
+            ColorOutput::Auto
+        }
+    } else {
+        ColorOutput::Auto
+    };
+
+    let use_color = should_use_color(color_output);
+
     if matches.is_present("list-languages") {
-        return Mode::ListLanguages;
+        return Mode::ListLanguages { use_color };
     }
 
     if let Some(path) = matches.value_of("dump-syntax") {
@@ -313,18 +329,6 @@ pub fn parse_args() -> Mode {
         DisplayMode::SideBySide
     };
 
-    let color_output = if let Some(color_when) = matches.value_of("color") {
-        if color_when == "always" {
-            ColorOutput::Always
-        } else if color_when == "never" {
-            ColorOutput::Never
-        } else {
-            ColorOutput::Auto
-        }
-    } else {
-        ColorOutput::Auto
-    };
-
     let background_color = match matches
         .value_of("background")
         .expect("Always present as we've given clap a default")
@@ -357,8 +361,6 @@ pub fn parse_args() -> Mode {
     let print_unchanged = !matches.is_present("skip-unchanged");
     let missing_as_empty = matches.is_present("missing-as-empty");
 
-    let use_color = should_use_color(color_output);
-
     let display_options = DisplayOptions {
         background_color,
         use_color,