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, 91 insertions, 107 deletions

diff --git a/alacritty/src/config/window.rs b/alacritty/src/config/window.rs
index ce36d23c..2d501b91 100644
--- a/alacritty/src/config/window.rs
+++ b/alacritty/src/config/window.rs
@@ -1,82 +1,77 @@
+use std::fmt::{self, Formatter};
 use std::os::raw::c_ulong;
 
 use glutin::window::Fullscreen;
 use log::error;
+use serde::de::{self, MapAccess, Visitor};
 use serde::{Deserialize, Deserializer};
-use serde_yaml::Value;
 
-use alacritty_terminal::config::{failure_default, option_explicit_none, LOG_TARGET_CONFIG};
+use alacritty_config_derive::ConfigDeserialize;
+use alacritty_terminal::config::LOG_TARGET_CONFIG;
 use alacritty_terminal::index::{Column, Line};
 
-use crate::config::ui_config::{DefaultTrueBool, Delta};
+use crate::config::ui_config::Delta;
 
 /// Default Alacritty name, used for window title and class.
 pub const DEFAULT_NAME: &str = "Alacritty";
 
-#[serde(default)]
-#[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
+#[derive(ConfigDeserialize, Debug, Clone, PartialEq, Eq)]
 pub struct WindowConfig {
     /// Initial position.
-    #[serde(deserialize_with = "failure_default")]
     pub position: Option<Delta<i32>>,
 
     /// Draw the window with title bar / borders.
-    #[serde(deserialize_with = "failure_default")]
     pub decorations: Decorations,
 
     /// Startup mode.
-    #[serde(deserialize_with = "failure_default")]
     pub startup_mode: StartupMode,
 
-    /// Window title.
-    #[serde(default = "default_title")]
-    pub title: String,
-
-    /// Window class.
-    #[serde(deserialize_with = "deserialize_class")]
-    pub class: Class,
-
     /// XEmbed parent.
-    #[serde(skip)]
+    #[config(skip)]
     pub embed: Option<c_ulong>,
 
     /// GTK theme variant.
-    #[serde(deserialize_with = "option_explicit_none")]
     pub gtk_theme_variant: Option<String>,
 
     /// Spread out additional padding evenly.
-    #[serde(deserialize_with = "failure_default")]
     pub dynamic_padding: bool,
 
+    /// Use dynamic title.
+    pub dynamic_title: bool,
+
+    /// Window title.
+    pub title: String,
+
+    /// Window class.
+    pub class: Class,
+
     /// Pixel padding.
-    #[serde(deserialize_with = "failure_default")]
     padding: Delta<u8>,
 
-    /// Use dynamic title.
-    #[serde(default, deserialize_with = "failure_default")]
-    dynamic_title: DefaultTrueBool,
-
     /// Initial dimensions.
-    #[serde(deserialize_with = "failure_default")]
     dimensions: Dimensions,
 }
 
-pub fn default_title() -> String {
-    DEFAULT_NAME.to_string()
+impl Default for WindowConfig {
+    fn default() -> Self {
+        Self {
+            dynamic_title: true,
+            title: DEFAULT_NAME.into(),
+            position: Default::default(),
+            decorations: Default::default(),
+            startup_mode: Default::default(),
+            embed: Default::default(),
+            gtk_theme_variant: Default::default(),
+            dynamic_padding: Default::default(),
+            class: Default::default(),
+            padding: Default::default(),
+            dimensions: Default::default(),
+        }
+    }
 }
 
 impl WindowConfig {
     #[inline]
-    pub fn dynamic_title(&self) -> bool {
-        self.dynamic_title.0
-    }
-
-    #[inline]
-    pub fn set_dynamic_title(&mut self, dynamic_title: bool) {
-        self.dynamic_title.0 = dynamic_title;
-    }
-
-    #[inline]
     pub fn dimensions(&self) -> Option<Dimensions> {
         if self.dimensions.columns.0 != 0
             && self.dimensions.lines.0 != 0
@@ -110,25 +105,7 @@ impl WindowConfig {
     }
 }
 
-impl Default for WindowConfig {
-    fn default() -> WindowConfig {
-        WindowConfig {
-            dimensions: Default::default(),
-            position: Default::default(),
-            padding: Default::default(),
-            decorations: Default::default(),
-            dynamic_padding: Default::default(),
-            startup_mode: Default::default(),
-            class: Default::default(),
-            embed: Default::default(),
-            gtk_theme_variant: Default::default(),
-            title: default_title(),
-            dynamic_title: Default::default(),
-        }
-    }
-}
-
-#[derive(Debug, Deserialize, Copy, Clone, PartialEq, Eq)]
+#[derive(ConfigDeserialize, Debug, Copy, Clone, PartialEq, Eq)]
 pub enum StartupMode {
     Windowed,
     Maximized,
@@ -143,17 +120,13 @@ impl Default for StartupMode {
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Deserialize)]
+#[derive(ConfigDeserialize, Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Decorations {
-    #[serde(rename = "full")]
     Full,
     #[cfg(target_os = "macos")]
-    #[serde(rename = "transparent")]
     Transparent,
     #[cfg(target_os = "macos")]
-    #[serde(rename = "buttonless")]
     Buttonless,
-    #[serde(rename = "none")]
     None,
 }
 
@@ -166,71 +139,82 @@ impl Default for Decorations {
 /// Window Dimensions.
 ///
 /// Newtype to avoid passing values incorrectly.
-#[serde(default)]
-#[derive(Default, Debug, Copy, Clone, Deserialize, PartialEq, Eq)]
+#[derive(ConfigDeserialize, Default, Debug, Copy, Clone, PartialEq, Eq)]
 pub struct Dimensions {
     /// Window width in character columns.
-    #[serde(deserialize_with = "failure_default")]
     pub columns: Column,
 
     /// Window Height in character lines.
-    #[serde(deserialize_with = "failure_default")]
     pub lines: Line,
 }
 
 /// Window class hint.
-#[serde(default)]
-#[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Class {
-    #[serde(deserialize_with = "deserialize_class_resource")]
     pub instance: String,
-
-    #[serde(deserialize_with = "deserialize_class_resource")]
     pub general: String,
 }
 
 impl Default for Class {
     fn default() -> Self {
-        Class { instance: DEFAULT_NAME.into(), general: DEFAULT_NAME.into() }
-    }
-}
-
-fn deserialize_class_resource<'a, D>(deserializer: D) -> Result<String, D::Error>
-where
-    D: Deserializer<'a>,
-{
-    let value = Value::deserialize(deserializer)?;
-    match String::deserialize(value) {
-        Ok(value) => Ok(value),
-        Err(err) => {
-            error!(
-                target: LOG_TARGET_CONFIG,
-                "Problem with config: {}, using default value {}", err, DEFAULT_NAME,
-            );
-
-            Ok(DEFAULT_NAME.into())
-        },
+        Self { instance: DEFAULT_NAME.into(), general: DEFAULT_NAME.into() }
     }
 }
 
-fn deserialize_class<'a, D>(deserializer: D) -> Result<Class, D::Error>
-where
-    D: Deserializer<'a>,
-{
-    let value = Value::deserialize(deserializer)?;
-
-    if let Value::String(instance) = value {
-        return Ok(Class { instance, general: DEFAULT_NAME.into() });
-    }
+impl<'de> Deserialize<'de> for Class {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct ClassVisitor;
+        impl<'a> Visitor<'a> for ClassVisitor {
+            type Value = Class;
+
+            fn expecting(&self, f: &mut Formatter<'_>) -> fmt::Result {
+                f.write_str("a mapping")
+            }
+
+            fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                Ok(Self::Value { instance: value.into(), ..Self::Value::default() })
+            }
+
+            fn visit_map<M>(self, mut map: M) -> Result<Self::Value, M::Error>
+            where
+                M: MapAccess<'a>,
+            {
+                let mut class = Self::Value::default();
+
+                while let Some((key, value)) = map.next_entry::<String, serde_yaml::Value>()? {
+                    match key.as_str() {
+                        "instance" => match String::deserialize(value) {
+                            Ok(instance) => class.instance = instance,
+                            Err(err) => {
+                                error!(
+                                    target: LOG_TARGET_CONFIG,
+                                    "Config error: class.instance: {}", err
+                                );
+                            },
+                        },
+                        "general" => match String::deserialize(value) {
+                            Ok(general) => class.general = general,
+                            Err(err) => {
+                                error!(
+                                    target: LOG_TARGET_CONFIG,
+                                    "Config error: class.instance: {}", err
+                                );
+                            },
+                        },
+                        _ => (),
+                    }
+                }
+
+                Ok(class)
+            }
+        }
 
-    match Class::deserialize(value) {
-        Ok(value) => Ok(value),
-        Err(err) => {
-            error!(
-                target: LOG_TARGET_CONFIG,
-                "Problem with config: {}; using class {}", err, DEFAULT_NAME
-            );
-            Ok(Class::default())
-        },
+        deserializer.deserialize_any(ClassVisitor)
     }
 }