feat: better error handling (introduce thiserror)

Cargo.lock

@@ -206,7 +206,7 @@ checksum = "ba009ff324d1fc1b900bd1fdb31564febe58a8ccc8a6fdbb93b543d33b13ca43"
 dependencies = [
  "getrandom",
  "libredox",
- "thiserror",
+ "thiserror 1.0.69",
 ]
 
 [[package]]
@@ -246,6 +246,7 @@ dependencies = [
  "crossterm",
  "dirs",
  "regex",
+ "thiserror 2.0.10",
 ]
 
 [[package]]
@@ -307,7 +308,16 @@ version = "1.0.69"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6aaf5339b578ea85b50e080feb250a3e8ae8cfcdff9a461c9ec2904bc923f52"
 dependencies = [
- "thiserror-impl",
+ "thiserror-impl 1.0.69",
+]
+
+[[package]]
+name = "thiserror"
+version = "2.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a3ac7f54ca534db81081ef1c1e7f6ea8a3ef428d2fc069097c079443d24124d3"
+dependencies = [
+ "thiserror-impl 2.0.10",
 ]
 
 [[package]]
@@ -321,6 +331,17 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thiserror-impl"
+version = "2.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e9465d30713b56a37ede7185763c3492a91be2f5fa68d958c44e41ab9248beb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.14"

Cargo.toml

@@ -10,4 +10,5 @@ crossterm = "0.27"
 regex = "1.11"
 anyhow = "1.0"
 dirs = "5.0"
+thiserror = "2"
 # clap = { version = "4.5", features = ["derive"] }

src/lib.rs

@@ -6,7 +6,7 @@ use crossterm::{
     terminal::DisableLineWrap,
 };
 use input::Input;
-use persist::{Session, SessionName};
+use persist::Session;
 use regex::Cache as RegexCache;
 use render::Render;
 
@@ -46,7 +46,7 @@ enum Field {
     TestString,
 }
 
-struct Change {
+pub struct Change {
     content: bool,
     cursor: bool,
 }

src/main.rs

@@ -6,7 +6,7 @@ use replay::{App, persist::Session};
 
 fn main() -> anyhow::Result<()> {
     let session = if let Some(name) = env::args().nth(1) {
-        Session::fetch(name).unwrap()
+        Session::fetch(name)?
     } else {
         Session::scratch()
     };

src/persist.rs

@@ -19,7 +19,7 @@ impl Display for SessionName {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(
             f,
-            "-- {} --",
+            "--- {} ---",
             if let Self::Name(name) = self {
                 name
             } else {
@@ -29,10 +29,22 @@ impl Display for SessionName {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, thiserror::Error)]
 pub enum Error {
+    #[error("session name contains invalid char: `{0}`")]
     InvalidName(char),
-    InvalidFormat,
+    #[error("session file contains invalid format: {0}")]
+    InvalidFormat(FormatError),
+}
+
+#[derive(thiserror::Error, Debug)]
+pub enum FormatError {
+    #[error("session file must include exactly 2 lines")]
+    Lines,
+    #[error("the cursor position and content must be separated with a `:`")]
+    Separator,
+    #[error("cursor position must be a string representation of a `usize`")]
+    Cursor,
 }
 
 pub struct Session {
@@ -94,6 +106,8 @@ impl Session {
 
 fn validate_name(name: &str) -> Result<(), Error> {
     if let Some(idx) = name.find(INVALID_CHARS) {
+        // This `unwrap` is okay, because we got that index from the `find`
+        // method, which means it must be in the bounds of the string
         Err(Error::InvalidName(name.chars().nth(idx).unwrap()))
     } else {
         Ok(())
@@ -104,7 +118,7 @@ fn parse_session(path: &Path) -> Result<(Input, Input), Error> {
     if let Ok(s) = fs::read_to_string(path) {
         let lines: Vec<_> = s.split('\n').collect();
         if lines.len() != 2 {
-            Err(Error::InvalidFormat)
+            Err(Error::InvalidFormat(FormatError::Lines))
         } else {
             let regex_query = parse_field(lines[0])?;
             let test_string = parse_field(lines[1])?;
@@ -128,8 +142,12 @@ fn get_path(name: &str) -> PathBuf {
 }
 
 fn parse_field(s: &str) -> Result<Input, Error> {
-    let (cursor, string) = s.split_once(':').ok_or(Error::InvalidFormat)?;
-    let cursor = cursor.parse().map_err(|_| Error::InvalidFormat)?;
+    let (cursor, string) = s
+        .split_once(':')
+        .ok_or(Error::InvalidFormat(FormatError::Separator))?;
+    let cursor = cursor
+        .parse()
+        .map_err(|_| Error::InvalidFormat(FormatError::Cursor))?;
     Ok(Input {
         string: string.to_owned(),
         cursor,