Replace serde's derive with custom proc macro

This replaces the existing `Deserialize` derive from serde with a
`ConfigDeserialize` derive. The goal of this new proc macro is to allow
a more error-friendly deserialization for the Alacritty configuration
file without having to manage a lot of boilerplate code inside the
configuration modules.

The first part of the derive macro is for struct deserialization. This
takes structs which have `Default` implemented and will only replace
fields which can be successfully deserialized. Otherwise the `log` crate
is used for printing errors. Since this deserialization takes the
default value from the struct instead of the value, it removes the
necessity for creating new types just to implement `Default` on them for
deserialization.

Additionally, the struct deserialization also checks for `Option` values
and makes sure that explicitly specifying `none` as text literal is
allowed for all options.

The other part of the derive macro is responsible for deserializing
enums. While only enums with Unit variants are supported, it will
automatically implement a deserializer for these enums which accepts any
form of capitalization.

Since this custom derive prevents us from using serde's attributes on
fields, some of the attributes have been reimplemented for
`ConfigDeserialize`. These include `#[config(flatten)]`,
`#[config(skip)]` and `#[config(alias = "alias)]`. The flatten attribute
is currently limited to at most one per struct.

Additionally the `#[config(deprecated = "optional message")]` attribute
allows easily defining uniform deprecation messages for fields on
structs.

1 files changed, 53 insertions, 76 deletions

diff --git a/alacritty/src/config/ui_config.rs b/alacritty/src/config/ui_config.rs
index 87b27b3e..25f9fb91 100644
--- a/alacritty/src/config/ui_config.rs
+++ b/alacritty/src/config/ui_config.rs
@@ -3,7 +3,8 @@ use std::path::PathBuf;
 use log::error;
 use serde::{Deserialize, Deserializer};
 
-use alacritty_terminal::config::{failure_default, Percentage, LOG_TARGET_CONFIG};
+use alacritty_config_derive::ConfigDeserialize;
+use alacritty_terminal::config::{Percentage, LOG_TARGET_CONFIG};
 
 use crate::config::bindings::{self, Binding, KeyBinding, MouseBinding};
 use crate::config::debug::Debug;
@@ -11,66 +12,52 @@ use crate::config::font::Font;
 use crate::config::mouse::Mouse;
 use crate::config::window::WindowConfig;
 
-#[derive(Debug, PartialEq, Deserialize)]
+#[derive(ConfigDeserialize, Debug, PartialEq)]
 pub struct UIConfig {
     /// Font configuration.
-    #[serde(default, deserialize_with = "failure_default")]
     pub font: Font,
 
     /// Window configuration.
-    #[serde(default, deserialize_with = "failure_default")]
     pub window: WindowConfig,
 
-    #[serde(default, deserialize_with = "failure_default")]
     pub mouse: Mouse,
 
-    /// Keybindings.
-    #[serde(default = "default_key_bindings", deserialize_with = "deserialize_key_bindings")]
-    pub key_bindings: Vec<KeyBinding>,
-
-    /// Bindings for the mouse.
-    #[serde(default = "default_mouse_bindings", deserialize_with = "deserialize_mouse_bindings")]
-    pub mouse_bindings: Vec<MouseBinding>,
-
     /// Debug options.
-    #[serde(default, deserialize_with = "failure_default")]
     pub debug: Debug,
 
     /// Send escape sequences using the alt key.
-    #[serde(default, deserialize_with = "failure_default")]
-    alt_send_esc: DefaultTrueBool,
+    pub alt_send_esc: bool,
 
     /// Live config reload.
-    #[serde(default, deserialize_with = "failure_default")]
-    live_config_reload: DefaultTrueBool,
-
-    /// Background opacity from 0.0 to 1.0.
-    #[serde(default, deserialize_with = "failure_default")]
-    background_opacity: Percentage,
+    pub live_config_reload: bool,
 
     /// Path where config was loaded from.
-    #[serde(skip)]
+    #[config(skip)]
     pub config_paths: Vec<PathBuf>,
 
-    // TODO: DEPRECATED
-    #[serde(default, deserialize_with = "failure_default")]
-    pub dynamic_title: Option<bool>,
+    /// Keybindings.
+    key_bindings: KeyBindings,
+
+    /// Bindings for the mouse.
+    mouse_bindings: MouseBindings,
+
+    /// Background opacity from 0.0 to 1.0.
+    background_opacity: Percentage,
 }
 
 impl Default for UIConfig {
     fn default() -> Self {
-        UIConfig {
+        Self {
+            alt_send_esc: true,
+            live_config_reload: true,
             font: Default::default(),
             window: Default::default(),
             mouse: Default::default(),
-            key_bindings: default_key_bindings(),
-            mouse_bindings: default_mouse_bindings(),
             debug: Default::default(),
-            alt_send_esc: Default::default(),
-            background_opacity: Default::default(),
-            live_config_reload: Default::default(),
-            dynamic_title: Default::default(),
             config_paths: Default::default(),
+            key_bindings: Default::default(),
+            mouse_bindings: Default::default(),
+            background_opacity: Default::default(),
         }
     }
 }
@@ -82,48 +69,50 @@ impl UIConfig {
     }
 
     #[inline]
-    pub fn dynamic_title(&self) -> bool {
-        self.dynamic_title.unwrap_or_else(|| self.window.dynamic_title())
+    pub fn key_bindings(&self) -> &[KeyBinding] {
+        &self.key_bindings.0.as_slice()
     }
 
     #[inline]
-    pub fn set_dynamic_title(&mut self, dynamic_title: bool) {
-        self.window.set_dynamic_title(dynamic_title);
+    pub fn mouse_bindings(&self) -> &[MouseBinding] {
+        self.mouse_bindings.0.as_slice()
     }
+}
 
-    /// Live config reload.
-    #[inline]
-    pub fn live_config_reload(&self) -> bool {
-        self.live_config_reload.0
-    }
+#[derive(Debug, PartialEq)]
+struct KeyBindings(Vec<KeyBinding>);
 
-    /// Send escape sequences using the alt key.
-    #[inline]
-    pub fn alt_send_esc(&self) -> bool {
-        self.alt_send_esc.0
+impl Default for KeyBindings {
+    fn default() -> Self {
+        Self(bindings::default_key_bindings())
     }
 }
 
-fn default_key_bindings() -> Vec<KeyBinding> {
-    bindings::default_key_bindings()
+impl<'de> Deserialize<'de> for KeyBindings {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Ok(Self(deserialize_bindings(deserializer, Self::default().0)?))
+    }
 }
 
-fn default_mouse_bindings() -> Vec<MouseBinding> {
-    bindings::default_mouse_bindings()
-}
+#[derive(Debug, PartialEq)]
+struct MouseBindings(Vec<MouseBinding>);
 
-fn deserialize_key_bindings<'a, D>(deserializer: D) -> Result<Vec<KeyBinding>, D::Error>
-where
-    D: Deserializer<'a>,
-{
-    deserialize_bindings(deserializer, bindings::default_key_bindings())
+impl Default for MouseBindings {
+    fn default() -> Self {
+        Self(bindings::default_mouse_bindings())
+    }
 }
 
-fn deserialize_mouse_bindings<'a, D>(deserializer: D) -> Result<Vec<MouseBinding>, D::Error>
-where
-    D: Deserializer<'a>,
-{
-    deserialize_bindings(deserializer, bindings::default_mouse_bindings())
+impl<'de> Deserialize<'de> for MouseBindings {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Ok(Self(deserialize_bindings(deserializer, Self::default().0)?))
+    }
 }
 
 fn deserialize_bindings<'a, D, T>(
@@ -143,7 +132,7 @@ where
         match Binding::<T>::deserialize(value) {
             Ok(binding) => bindings.push(binding),
             Err(err) => {
-                error!(target: LOG_TARGET_CONFIG, "Problem with config: {}; ignoring binding", err);
+                error!(target: LOG_TARGET_CONFIG, "Config error: {}; ignoring binding", err);
             },
         }
     }
@@ -158,23 +147,11 @@ where
     Ok(bindings)
 }
 
-#[derive(Deserialize, Copy, Clone, Debug, PartialEq, Eq)]
-pub struct DefaultTrueBool(pub bool);
-
-impl Default for DefaultTrueBool {
-    fn default() -> Self {
-        DefaultTrueBool(true)
-    }
-}
-
 /// A delta for a point in a 2 dimensional plane.
-#[serde(default, bound(deserialize = "T: Deserialize<'de> + Default"))]
-#[derive(Clone, Copy, Debug, Default, Deserialize, PartialEq, Eq)]
-pub struct Delta<T: Default + PartialEq + Eq> {
+#[derive(ConfigDeserialize, Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct Delta<T: Default> {
     /// Horizontal change.
-    #[serde(deserialize_with = "failure_default")]
     pub x: T,
     /// Vertical change.
-    #[serde(deserialize_with = "failure_default")]
     pub y: T,
 }