Add IPC config subcommand

This patch adds a new mechanism for changing configuration options
without editing the configuration file, by sending options to running
instances through `alacritty msg`.

Each window will load Alacritty's configuration file by default and then
accept IPC messages for config updates using the `alacritty msg config`
subcommand. By default all windows will be updated, individual windows
can be addressed using `alacritty msg config --window-id
"$ALACRITTY_WINDOW_ID"`.

Each option will replace the config's current value and cannot be reset
until Alacritty is restarted or the option is overwritten with a new
value.

Configuration options are passed in the format `field.subfield=value`,
where `value` is interpreted as yaml.

Closes #472.

2 files changed, 78 insertions, 0 deletions

diff --git a/alacritty_config/Cargo.toml b/alacritty_config/Cargo.toml
new file mode 100644
index 00000000..3b287f43
--- /dev/null
+++ b/alacritty_config/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "alacritty_config"
+version = "0.1.0"
+authors = ["Christian Duerr <contact@christianduerr.com>"]
+license = "MIT/Apache-2.0"
+description = "Alacritty configuration abstractions"
+homepage = "https://github.com/alacritty/alacritty"
+edition = "2021"
+rust-version = "1.57.0"
+
+[dependencies]
+log = { version = "0.4.17", features = ["serde"] }
+serde_yaml = "0.8.24"
+serde = "1.0.137"
diff --git a/alacritty_config/src/lib.rs b/alacritty_config/src/lib.rs
new file mode 100644
index 00000000..7a467650
--- /dev/null
+++ b/alacritty_config/src/lib.rs
@@ -0,0 +1,64 @@
+use std::collections::HashMap;
+use std::error::Error;
+
+use log::LevelFilter;
+use serde::Deserialize;
+use serde_yaml::Value;
+
+pub trait SerdeReplace {
+    fn replace(&mut self, key: &str, value: Value) -> Result<(), Box<dyn Error>>;
+}
+
+macro_rules! impl_replace {
+    ($($ty:ty),*$(,)*) => {
+        $(
+            impl SerdeReplace for $ty {
+                fn replace(&mut self, key: &str, value: Value) -> Result<(), Box<dyn Error>> {
+                    replace_simple(self, key, value)
+                }
+            }
+        )*
+    };
+}
+
+#[rustfmt::skip]
+impl_replace!(
+    usize, u8, u16, u32, u64, u128,
+    isize, i8, i16, i32, i64, i128,
+    f32, f64,
+    bool,
+    char,
+    String,
+    LevelFilter,
+);
+
+fn replace_simple<'de, D>(data: &mut D, key: &str, value: Value) -> Result<(), Box<dyn Error>>
+where
+    D: Deserialize<'de>,
+{
+    if !key.is_empty() {
+        let error = format!("Fields \"{}\" do not exist", key);
+        return Err(error.into());
+    }
+    *data = D::deserialize(value)?;
+
+    Ok(())
+}
+
+impl<'de, T: Deserialize<'de>> SerdeReplace for Vec<T> {
+    fn replace(&mut self, key: &str, value: Value) -> Result<(), Box<dyn Error>> {
+        replace_simple(self, key, value)
+    }
+}
+
+impl<'de, T: Deserialize<'de>> SerdeReplace for Option<T> {
+    fn replace(&mut self, key: &str, value: Value) -> Result<(), Box<dyn Error>> {
+        replace_simple(self, key, value)
+    }
+}
+
+impl<'de, T: Deserialize<'de>> SerdeReplace for HashMap<String, T> {
+    fn replace(&mut self, key: &str, value: Value) -> Result<(), Box<dyn Error>> {
+        replace_simple(self, key, value)
+    }
+}