Add error handling

Added error and result types, removed a lot of unwraps, expects and
panics, but there are still some left in the tarsila crate, especially
in GUI code.

README.md

@@ -33,8 +33,8 @@ bugs, incomplete or missing features and suboptimal performance here and there.
 Some of the main gaps currently are:
 
 * Works as intended on Linux, but there are some compatibility issues with MacOS
-  (file dialog window does not open), and status on Windows is unknown;
-* No error handling, everything panics;
+  (file dialog window does not open, modifier keys do not work); Windows is
+  reported to be working as intended;
 * There are a few unit tests, but integration tests are missing, and coverage is
   far from 100%;
 * There is room to improve when it comes to performance

lapix/Cargo.toml

@@ -19,6 +19,7 @@ test-utils = []
 bincode = "1.3.3"
 image = "0.24.5"
 serde = { version = "1.0.152", features = ["derive"] }
+thiserror = "1.0.40"
 
 [dev-dependencies]
 test-case = "2.2.2"

lapix/src/bitmap.rs

@@ -1,4 +1,4 @@
-use crate::{color, Color, Point, Size};
+use crate::{color, Color, Error, Point, Result, Size};
 
 // TODO rename this trait
 /// Represents a 2D matrix of pixels (an image)
@@ -33,29 +33,26 @@ pub trait Bitmap: Clone {
 
     // TODO: use this and next method to save/load files
     /// Get the the PNG representation of this image as a sequence of bytes
-    fn png_bytes(&self) -> Vec<u8> {
+    fn png_bytes(&self) -> Result<Vec<u8>> {
         let img = image::RgbaImage::from_raw(
             self.width() as u32,
             self.height() as u32,
             self.bytes().to_owned(),
         )
-        .expect("Failed to generate image from bytes");
+        .ok_or(Error::FailedImageFromRaw)?;
 
         let vec = Vec::<u8>::new();
         let mut vec = std::io::Cursor::new(vec);
-        img.write_to(&mut vec, image::ImageOutputFormat::Png)
-            .unwrap(); // never fails
+        img.write_to(&mut vec, image::ImageOutputFormat::Png)?;
 
-        vec.into_inner()
+        Ok(vec.into_inner())
     }
 
     /// Create a new image from a sequence of bytes read from an image file
     /// (e.g. PNG or JPG)
-    fn from_file_bytes(bytes: Vec<u8>) -> Self {
-        let reader = image::io::Reader::new(std::io::Cursor::new(bytes))
-            .with_guessed_format()
-            .unwrap(); // never fails
-        let img = reader.decode().expect("failed to decode image");
+    fn try_from_file_bytes(bytes: Vec<u8>) -> Result<Self> {
+        let reader = image::io::Reader::new(std::io::Cursor::new(bytes)).with_guessed_format()?;
+        let img = reader.decode()?;
         let img = img.into_rgba8();
 
         let size: Size<i32> = (img.width() as i32, img.height() as i32).into();
@@ -66,7 +63,7 @@ pub trait Bitmap: Clone {
             bitmap.set_pixel((x as i32, y as i32).into(), color);
         }
 
-        bitmap
+        Ok(bitmap)
     }
 }
 

lapix/src/error.rs

@@ -0,0 +1,23 @@
+use thiserror::Error;
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error("Failed to generate image from raw data")]
+    FailedImageFromRaw,
+    #[error("No free image found")]
+    MissingFreeImage,
+    #[error("Unsupported image format")]
+    UnsupportedImageFormat,
+    #[error("Drawing action has not started")]
+    DrawingNotStarted,
+    #[error("Image error: {0}")]
+    ImageError(#[from] image::ImageError),
+    #[error("IO error: {0}")]
+    IoError(#[from] std::io::Error),
+    #[error("Bug: reversal list is not set")]
+    ReversalNotSet,
+    #[error("Codec error: {0}")]
+    CodecError(#[from] bincode::Error),
+}

lapix/src/lib.rs

@@ -5,6 +5,7 @@ mod action;
 mod bitmap;
 mod canvas;
 pub mod color;
+mod error;
 mod event;
 mod floating;
 pub mod graphics;
@@ -20,6 +21,7 @@ use action::{Action, AtomicAction};
 pub use bitmap::Bitmap;
 pub use canvas::{Canvas, CanvasEffect};
 pub use color::Color;
+pub use error::{Error, Result};
 pub use event::Event;
 pub use floating::FreeImage;
 pub use layer::{Layer, Layers};

lapix/src/palette.rs

@@ -1,4 +1,4 @@
-use crate::{util, Color};
+use crate::{util, Color, Result};
 use serde::{Deserialize, Serialize};
 
 const MAX_PALETTE: usize = 200;
@@ -28,9 +28,10 @@ impl Default for Palette {
 }
 
 impl Palette {
-    pub fn from_file(path: &str) -> Self {
-        let img = util::load_img_from_file(path);
-        Self::from_image(img)
+    pub fn from_file(path: &str) -> Result<Self> {
+        let img = util::load_img_from_file(path)?;
+
+        Ok(Self::from_image(img))
     }
 
     fn from_image(img: image::RgbaImage) -> Self {