Add CLI parameter to override config options

This uses the facilities added in
3c3e6870dedad56b270f5b65ea57d5a6e46b1de6 to allow overriding individual
configuration file options dynamically from the CLI using the
--options/-o parameter.

Fixes #1258.

7 files changed, 239 insertions, 88 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b32a0905..f1cac476 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - New Ctrl+C binding to cancel search and leave vi mode
 - Escapes for double underlines (`CSI 4 : 2 m`) and underline reset (`CSI 4 : 0 m`)
 - Configuration file option for sourcing other files (`import`)
+- CLI parameter `--option`/`-o` to override any configuration field
 
 ### Changed
 
diff --git a/alacritty/src/cli.rs b/alacritty/src/cli.rs
index 5da6332b..418e3791 100644
--- a/alacritty/src/cli.rs
+++ b/alacritty/src/cli.rs
@@ -3,10 +3,12 @@ use std::path::PathBuf;
 
 use clap::{crate_authors, crate_description, crate_name, crate_version, App, Arg};
 use log::{self, error, LevelFilter};
+use serde_yaml::Value;
 
 use alacritty_terminal::config::Program;
 use alacritty_terminal::index::{Column, Line};
 
+use crate::config::serde_utils;
 use crate::config::ui_config::Delta;
 use crate::config::window::{Dimensions, DEFAULT_NAME};
 use crate::config::Config;
@@ -32,9 +34,10 @@ pub struct Options {
     pub log_level: LevelFilter,
     pub command: Option<Program>,
     pub hold: bool,
-    pub working_dir: Option<PathBuf>,
-    pub config: Option<PathBuf>,
+    pub working_directory: Option<PathBuf>,
+    pub config_path: Option<PathBuf>,
     pub persistent_logging: bool,
+    pub config_options: Value,
 }
 
 impl Default for Options {
@@ -52,9 +55,10 @@ impl Default for Options {
             log_level: LevelFilter::Warn,
             command: None,
             hold: false,
-            working_dir: None,
-            config: None,
+            working_directory: None,
+            config_path: None,
             persistent_logging: false,
+            config_options: Value::Null,
         }
     }
 }
@@ -168,11 +172,18 @@ impl Options {
                     .short("e")
                     .multiple(true)
                     .takes_value(true)
-                    .min_values(1)
                     .allow_hyphen_values(true)
                     .help("Command and args to execute (must be last argument)"),
             )
             .arg(Arg::with_name("hold").long("hold").help("Remain open after child process exits"))
+            .arg(
+                Arg::with_name("option")
+                    .long("option")
+                    .short("o")
+                    .multiple(true)
+                    .takes_value(true)
+                    .help("Override configuration file options [example: window.title=Alacritty]"),
+            )
             .get_matches();
 
         if matches.is_present("ref-test") {
@@ -231,11 +242,11 @@ impl Options {
         }
 
         if let Some(dir) = matches.value_of("working-directory") {
-            options.working_dir = Some(PathBuf::from(dir.to_string()));
+            options.working_directory = Some(PathBuf::from(dir.to_string()));
         }
 
         if let Some(path) = matches.value_of("config-file") {
-            options.config = Some(PathBuf::from(path.to_string()));
+            options.config_path = Some(PathBuf::from(path.to_string()));
         }
 
         if let Some(mut args) = matches.values_of("command") {
@@ -251,23 +262,47 @@ impl Options {
             options.hold = true;
         }
 
+        if let Some(config_options) = matches.values_of("option") {
+            for option in config_options {
+                match option_as_value(option) {
+                    Ok(value) => {
+                        options.config_options = serde_utils::merge(options.config_options, value);
+                    },
+                    Err(_) => eprintln!("Invalid CLI config option: {:?}", option),
+                }
+            }
+        }
+
         options
     }
 
+    /// Configuration file path.
     pub fn config_path(&self) -> Option<PathBuf> {
-        self.config.clone()
+        self.config_path.clone()
     }
 
-    pub fn into_config(self, mut config: Config) -> Config {
-        match self.working_dir.or_else(|| config.working_directory.take()) {
-            Some(ref wd) if !wd.is_dir() => error!("Unable to set working directory to {:?}", wd),
-            wd => config.working_directory = wd,
+    /// CLI config options as deserializable serde value.
+    pub fn config_options(&self) -> &Value {
+        &self.config_options
+    }
+
+    /// Override configuration file with options from the CLI.
+    pub fn override_config(&self, config: &mut Config) {
+        if let Some(working_directory) = &self.working_directory {
+            if working_directory.is_dir() {
+                config.working_directory = Some(working_directory.to_owned());
+            } else {
+                error!("Invalid working directory: {:?}", working_directory);
+            }
         }
 
         if let Some(lcr) = self.live_config_reload {
             config.ui_config.set_live_config_reload(lcr);
         }
-        config.shell = self.command.or(config.shell);
+
+        if let Some(command) = &self.command {
+            config.shell = Some(command.clone());
+        }
 
         config.hold = self.hold;
 
@@ -275,12 +310,12 @@ impl Options {
         config.ui_config.set_dynamic_title(dynamic_title);
 
         replace_if_some(&mut config.ui_config.window.dimensions, self.dimensions);
-        replace_if_some(&mut config.ui_config.window.title, self.title);
-        config.ui_config.window.position = self.position.or(config.ui_config.window.position);
-        config.ui_config.window.embed = self.embed.and_then(|embed| embed.parse().ok());
-        replace_if_some(&mut config.ui_config.window.class.instance, self.class_instance);
-        replace_if_some(&mut config.ui_config.window.class.general, self.class_general);
+        replace_if_some(&mut config.ui_config.window.title, self.title.clone());
+        replace_if_some(&mut config.ui_config.window.class.instance, self.class_instance.clone());
+        replace_if_some(&mut config.ui_config.window.class.general, self.class_general.clone());
 
+        config.ui_config.window.position = self.position.or(config.ui_config.window.position);
+        config.ui_config.window.embed = self.embed.as_ref().and_then(|embed| embed.parse().ok());
         config.ui_config.debug.print_events |= self.print_events;
         config.ui_config.debug.log_level = max(config.ui_config.debug.log_level, self.log_level);
         config.ui_config.debug.ref_test |= self.ref_test;
@@ -290,8 +325,6 @@ impl Options {
             config.ui_config.debug.log_level =
                 max(config.ui_config.debug.log_level, LevelFilter::Info);
         }
-
-        config
     }
 }
 
@@ -301,28 +334,54 @@ fn replace_if_some<T>(option: &mut T, value: Option<T>) {
     }
 }
 
+/// Format an option in the format of `parent.field=value` to a serde Value.
+fn option_as_value(option: &str) -> Result<Value, serde_yaml::Error> {
+    let mut yaml_text = String::with_capacity(option.len());
+    let mut closing_brackets = String::new();
+
+    for (i, c) in option.chars().enumerate() {
+        match c {
+            '=' => {
+                yaml_text.push_str(": ");
+                yaml_text.push_str(&option[i + 1..]);
+                break;
+            },
+            '.' => {
+                yaml_text.push_str(": {");
+                closing_brackets.push('}');
+            },
+            _ => yaml_text.push(c),
+        }
+    }
+
+    yaml_text += &closing_brackets;
+
+    serde_yaml::from_str(&yaml_text)
+}
+
 #[cfg(test)]
 mod tests {
-    use crate::cli::Options;
-    use crate::config::Config;
+    use super::*;
+
+    use serde_yaml::mapping::Mapping;
 
     #[test]
     fn dynamic_title_ignoring_options_by_default() {
-        let config = Config::default();
+        let mut config = Config::default();
         let old_dynamic_title = config.ui_config.dynamic_title();
 
-        let config = Options::default().into_config(config);
+        Options::default().override_config(&mut config);
 
         assert_eq!(old_dynamic_title, config.ui_config.dynamic_title());
     }
 
     #[test]
     fn dynamic_title_overridden_by_options() {
-        let config = Config::default();
+        let mut config = Config::default();
 
         let mut options = Options::default();
         options.title = Some("foo".to_owned());
-        let config = options.into_config(config);
+        options.override_config(&mut config);
 
         assert!(!config.ui_config.dynamic_title());
     }
@@ -332,8 +391,45 @@ mod tests {
         let mut config = Config::default();
 
         config.ui_config.window.title = "foo".to_owned();
-        let config = Options::default().into_config(config);
+        Options::default().override_config(&mut config);
 
         assert!(config.ui_config.dynamic_title());
     }
+
+    #[test]
+    fn valid_option_as_value() {
+        // Test with a single field.
+        let value = option_as_value("field=true").unwrap();
+
+        let mut mapping = Mapping::new();
+        mapping.insert(Value::String(String::from("field")), Value::Bool(true));
+
+        assert_eq!(value, Value::Mapping(mapping));
+
+        // Test with nested fields
+        let value = option_as_value("parent.field=true").unwrap();
+
+        let mut parent_mapping = Mapping::new();
+        parent_mapping.insert(Value::String(String::from("field")), Value::Bool(true));
+        let mut mapping = Mapping::new();
+        mapping.insert(Value::String(String::from("parent")), Value::Mapping(parent_mapping));
+
+        assert_eq!(value, Value::Mapping(mapping));
+    }
+
+    #[test]
+    fn invalid_option_as_value() {
+        let value = option_as_value("}");
+        assert!(value.is_err());
+    }
+
+    #[test]
+    fn float_option_as_value() {
+        let value = option_as_value("float=3.4").unwrap();
+
+        let mut expected = Mapping::new();
+        expected.insert(Value::String(String::from("float")), Value::Number(3.4.into()));
+
+        assert_eq!(value, Value::Mapping(expected));
+    }
 }
diff --git a/alacritty/src/config/mod.rs b/alacritty/src/config/mod.rs
index 243f1bae..56a12c7c 100644
--- a/alacritty/src/config/mod.rs
+++ b/alacritty/src/config/mod.rs
@@ -2,7 +2,7 @@ use std::fmt::{self, Display, Formatter};
 use std::path::PathBuf;
 use std::{env, fs, io};
 
-use log::{error, warn};
+use log::{error, info, warn};
 use serde::Deserialize;
 use serde_yaml::mapping::Mapping;
 use serde_yaml::Value;
@@ -12,13 +12,14 @@ use alacritty_terminal::config::{Config as TermConfig, LOG_TARGET_CONFIG};
 pub mod debug;
 pub mod font;
 pub mod monitor;
+pub mod serde_utils;
 pub mod ui_config;
 pub mod window;
 
 mod bindings;
 mod mouse;
-mod serde_utils;
 
+use crate::cli::Options;
 pub use crate::config::bindings::{Action, Binding, Key, ViAction};
 #[cfg(test)]
 pub use crate::config::mouse::{ClickHandler, Mouse};
@@ -94,48 +95,42 @@ impl From<serde_yaml::Error> for Error {
     }
 }
 
-/// Get the location of the first found default config file paths
-/// according to the following order:
-///
-/// 1. $XDG_CONFIG_HOME/alacritty/alacritty.yml
-/// 2. $XDG_CONFIG_HOME/alacritty.yml
-/// 3. $HOME/.config/alacritty/alacritty.yml
-/// 4. $HOME/.alacritty.yml
-#[cfg(not(windows))]
-pub fn installed_config() -> Option<PathBuf> {
-    // Try using XDG location by default.
-    xdg::BaseDirectories::with_prefix("alacritty")
-        .ok()
-        .and_then(|xdg| xdg.find_config_file("alacritty.yml"))
-        .or_else(|| {
-            xdg::BaseDirectories::new()
-                .ok()
-                .and_then(|fallback| fallback.find_config_file("alacritty.yml"))
-        })
-        .or_else(|| {
-            if let Ok(home) = env::var("HOME") {
-                // Fallback path: $HOME/.config/alacritty/alacritty.yml.
-                let fallback = PathBuf::from(&home).join(".config/alacritty/alacritty.yml");
-                if fallback.exists() {
-                    return Some(fallback);
-                }
-                // Fallback path: $HOME/.alacritty.yml.
-                let fallback = PathBuf::from(&home).join(".alacritty.yml");
-                if fallback.exists() {
-                    return Some(fallback);
-                }
-            }
-            None
-        })
+/// Load the configuration file.
+pub fn load(options: &Options) -> Config {
+    // Get config path.
+    let config_path = match options.config_path().or_else(installed_config) {
+        Some(path) => path,
+        None => {
+            info!(target: LOG_TARGET_CONFIG, "No config file found; using default");
+            return Config::default();
+        },
+    };
+
+    // Load config, falling back to the default on error.
+    let config_options = options.config_options().clone();
+    let mut config = load_from(&config_path, config_options).unwrap_or_default();
+
+    // Override config with CLI options.
+    options.override_config(&mut config);
+
+    config
 }
 
-#[cfg(windows)]
-pub fn installed_config() -> Option<PathBuf> {
-    dirs::config_dir().map(|path| path.join("alacritty\\alacritty.yml")).filter(|new| new.exists())
+/// Attempt to reload the configuration file.
+pub fn reload(config_path: &PathBuf, options: &Options) -> Result<Config> {
+    // Load config, propagating errors.
+    let config_options = options.config_options().clone();
+    let mut config = load_from(&config_path, config_options)?;
+
+    // Override config with CLI options.
+    options.override_config(&mut config);
+
+    Ok(config)
 }
 
-pub fn load_from(path: &PathBuf) -> Result<Config> {
-    match read_config(path) {
+/// Load configuration file and log errors.
+fn load_from(path: &PathBuf, cli_config: Value) -> Result<Config> {
+    match read_config(path, cli_config) {
         Ok(config) => Ok(config),
         Err(err) => {
             error!(target: LOG_TARGET_CONFIG, "Unable to load config {:?}: {}", path, err);
@@ -144,10 +139,15 @@ pub fn load_from(path: &PathBuf) -> Result<Config> {
     }
 }
 
-fn read_config(path: &PathBuf) -> Result<Config> {
+/// Deserialize configuration file from path.
+fn read_config(path: &PathBuf, cli_config: Value) -> Result<Config> {
     let mut config_paths = Vec::new();
-    let config_value = parse_config(&path, &mut config_paths, IMPORT_RECURSION_LIMIT)?;
+    let mut config_value = parse_config(&path, &mut config_paths, IMPORT_RECURSION_LIMIT)?;
+
+    // Override config with CLI options.
+    config_value = serde_utils::merge(config_value, cli_config);
 
+    // Deserialize to concrete type.
     let mut config = Config::deserialize(config_value)?;
     config.ui_config.config_paths = config_paths;
 
@@ -231,6 +231,46 @@ fn load_imports(config: &Value, config_paths: &mut Vec<PathBuf>, recursion_limit
     merged
 }
 
+/// Get the location of the first found default config file paths
+/// according to the following order:
+///
+/// 1. $XDG_CONFIG_HOME/alacritty/alacritty.yml
+/// 2. $XDG_CONFIG_HOME/alacritty.yml
+/// 3. $HOME/.config/alacritty/alacritty.yml
+/// 4. $HOME/.alacritty.yml
+#[cfg(not(windows))]
+fn installed_config() -> Option<PathBuf> {
+    // Try using XDG location by default.
+    xdg::BaseDirectories::with_prefix("alacritty")
+        .ok()
+        .and_then(|xdg| xdg.find_config_file("alacritty.yml"))
+        .or_else(|| {
+            xdg::BaseDirectories::new()
+                .ok()
+                .and_then(|fallback| fallback.find_config_file("alacritty.yml"))
+        })
+        .or_else(|| {
+            if let Ok(home) = env::var("HOME") {
+                // Fallback path: $HOME/.config/alacritty/alacritty.yml.
+                let fallback = PathBuf::from(&home).join(".config/alacritty/alacritty.yml");
+                if fallback.exists() {
+                    return Some(fallback);
+                }
+                // Fallback path: $HOME/.alacritty.yml.
+                let fallback = PathBuf::from(&home).join(".alacritty.yml");
+                if fallback.exists() {
+                    return Some(fallback);
+                }
+            }
+            None
+        })
+}
+
+#[cfg(windows)]
+fn installed_config() -> Option<PathBuf> {
+    dirs::config_dir().map(|path| path.join("alacritty\\alacritty.yml")).filter(|new| new.exists())
+}
+
 fn print_deprecation_warnings(config: &Config) {
     if config.scrolling.faux_multiplier().is_some() {
         warn!(
@@ -282,7 +322,7 @@ mod tests {
     #[test]
     fn config_read_eof() {
         let config_path: PathBuf = DEFAULT_ALACRITTY_CONFIG.into();
-        let mut config = read_config(&config_path).unwrap();
+        let mut config = read_config(&config_path, Value::Null).unwrap();
         config.ui_config.config_paths = Vec::new();
         assert_eq!(config, Config::default());
     }
diff --git a/alacritty/src/config/serde_utils.rs b/alacritty/src/config/serde_utils.rs
index ecf1c858..beb9c36b 100644
--- a/alacritty/src/config/serde_utils.rs
+++ b/alacritty/src/config/serde_utils.rs
@@ -16,6 +16,7 @@ pub fn merge(base: Value, replacement: Value) -> Value {
         (Value::Mapping(base), Value::Mapping(replacement)) => {
             Value::Mapping(merge_mapping(base, replacement))
         },
+        (value, Value::Null) => value,
         (_, value) => value,
     }
 }
@@ -54,6 +55,10 @@ mod tests {
         let base = Value::String(String::new());
         let replacement = Value::String(String::from("test"));
         assert_eq!(merge(base, replacement.clone()), replacement);
+
+        let base = Value::Mapping(Mapping::new());
+        let replacement = Value::Null;
+        assert_eq!(merge(base.clone(), replacement), base);
     }
 
     #[test]
diff --git a/alacritty/src/event.rs b/alacritty/src/event.rs
index d0ce3601..c3e1b6c8 100644
--- a/alacritty/src/event.rs
+++ b/alacritty/src/event.rs
@@ -39,7 +39,7 @@ use alacritty_terminal::term::{ClipboardType, SizeInfo, Term, TermMode};
 #[cfg(not(windows))]
 use alacritty_terminal::tty;
 
-use crate::cli::Options;
+use crate::cli::Options as CLIOptions;
 use crate::clipboard::Clipboard;
 use crate::config;
 use crate::config::Config;
@@ -139,6 +139,7 @@ pub struct ActionContext<'a, N, T> {
     pub urls: &'a Urls,
     pub scheduler: &'a mut Scheduler,
     pub search_state: &'a mut SearchState,
+    cli_options: &'a CLIOptions,
     font_size: &'a mut Size,
 }
 
@@ -693,6 +694,7 @@ pub struct Processor<N> {
     font_size: Size,
     event_queue: Vec<GlutinEvent<'static, Event>>,
     search_state: SearchState,
+    cli_options: CLIOptions,
 }
 
 impl<N: Notify + OnResize> Processor<N> {
@@ -704,6 +706,7 @@ impl<N: Notify + OnResize> Processor<N> {
         message_buffer: MessageBuffer,
         config: Config,
         display: Display,
+        cli_options: CLIOptions,
     ) -> Processor<N> {
         #[cfg(not(any(target_os = "macos", windows)))]
         let clipboard = Clipboard::new(display.window.wayland_display());
@@ -723,6 +726,7 @@ impl<N: Notify + OnResize> Processor<N> {
             event_queue: Vec::new(),
             clipboard,
             search_state: SearchState::new(),
+            cli_options,
         }
     }
 
@@ -826,6 +830,7 @@ impl<N: Notify + OnResize> Processor<N> {
                 urls: &self.display.urls,
                 scheduler: &mut scheduler,
                 search_state: &mut self.search_state,
+                cli_options: &self.cli_options,
                 event_loop,
             };
             let mut processor = input::Processor::new(context, &self.display.highlighted_url);
@@ -1051,14 +1056,11 @@ impl<N: Notify + OnResize> Processor<N> {
             processor.ctx.display_update_pending.dirty = true;
         }
 
-        let config = match config::load_from(&path) {
+        let config = match config::reload(&path, &processor.ctx.cli_options) {
             Ok(config) => config,
             Err(_) => return,
         };
 
-        let options = Options::new();
-        let config = options.into_config(config);
-
         processor.ctx.terminal.update_config(&config);
 
         // Reload cursor if we've changed its thickness.
diff --git a/alacritty/src/main.rs b/alacritty/src/main.rs
index 21c4804c..838ce4d2 100644
--- a/alacritty/src/main.rs
+++ b/alacritty/src/main.rs
@@ -83,12 +83,7 @@ fn main() {
         .expect("Unable to initialize logger");
 
     // Load configuration file.
-    let config_path = options.config_path().or_else(config::installed_config);
-    let config = config_path
-        .as_ref()
-        .and_then(|path| config::load_from(path).ok())
-        .unwrap_or_else(Config::default);
-    let config = options.into_config(config);
+    let config = config::load(&options);
 
     // Update the log level from config.
     log::set_max_level(config.ui_config.debug.log_level);
@@ -104,7 +99,7 @@ fn main() {
     let persistent_logging = config.ui_config.debug.persistent_logging;
 
     // Run Alacritty.
-    if let Err(err) = run(window_event_loop, config) {
+    if let Err(err) = run(window_event_loop, config, options) {
         error!("Alacritty encountered an unrecoverable error:\n\n\t{}\n", err);
         std::process::exit(1);
     }
@@ -121,7 +116,11 @@ fn main() {
 ///
 /// Creates a window, the terminal state, PTY, I/O event loop, input processor,
 /// config change monitor, and runs the main display loop.
-fn run(window_event_loop: GlutinEventLoop<Event>, config: Config) -> Result<(), Box<dyn Error>> {
+fn run(
+    window_event_loop: GlutinEventLoop<Event>,
+    config: Config,
+    options: Options,
+) -> Result<(), Box<dyn Error>> {
     info!("Welcome to Alacritty");
 
     info!("Configuration files loaded from:");
@@ -189,8 +188,13 @@ fn run(window_event_loop: GlutinEventLoop<Event>, config: Config) -> Result<(),
     let message_buffer = MessageBuffer::new();
 
     // Event processor.
-    let mut processor =
-        Processor::new(event_loop::Notifier(loop_tx.clone()), message_buffer, config, display);
+    let mut processor = Processor::new(
+        event_loop::Notifier(loop_tx.clone()),
+        message_buffer,
+        config,
+        display,
+        options,
+    );
 
     // Kick off the I/O thread.
     let io_thread = event_loop.spawn();
diff --git a/extra/alacritty.man b/extra/alacritty.man
index 392f8c3b..8d89d2c5 100644
--- a/extra/alacritty.man
+++ b/extra/alacritty.man
@@ -64,15 +64,18 @@ On Windows, the configuration file is located at %APPDATA%\\alacritty\\alacritty
 \fB\-d\fR, \fB\-\-dimensions\fR <columns> <lines>
 Defines the window dimensions. Falls back to size specified by window manager if set to 0x0 [default: 0x0]
 .TP
+\fB\-\-embed\fR <parent>
+Defines the X11 window ID (as a decimal integer) to embed Alacritty within
+.TP
+\fB\-o\fR, \fB\-\-option\fR <option>...
+Override configuration file options [example: window.title=Alacritty]
+.TP
 \fB\-\-position\fR <x-pos> <y-pos>
 Defines the window position. Falls back to position specified by window manager if unset [default: unset]
 .TP
 \fB\-t\fR, \fB\-\-title\fR <title>
 Defines the window title [default: Alacritty]
 .TP
-\fB\-\-embed\fR <parent>
-Defines the X11 window ID (as a decimal integer) to embed Alacritty within
-.TP
 \fB\-\-working\-directory\fR <working\-directory>
 Start the shell in the specified working directory
 .SH "SEE ALSO"