chore: improve error message for failed std::fs::read calls

crates/apt-convert/src/lib.rs

@@ -25,6 +25,8 @@ use thiserror::Error;
 pub enum Error {
     #[error("apt error: {0}")]
     Apt(#[from] apt::Error),
+    #[error("loading APT movie {}: {source}", base.display())]
+    LoadMovie { base: PathBuf, source: apt::Error },
     #[error("apt-aux error: {0}")]
     Aux(String),
     #[error("swf read error: {0}")]
@@ -92,7 +94,10 @@ pub struct ConvertedMovie {
 /// those too.
 pub fn convert_movie(base: &Path, options: &ConvertOptions) -> Result<Vec<u8>> {
     let base = apt::base_path(base);
-    let file = apt::AptFile::load(&base)?;
+    let file = apt::AptFile::load(&base).map_err(|source| Error::LoadMovie {
+        base: base.clone(),
+        source,
+    })?;
     convert_loaded_movie(&base, &file, options)
 }
 
@@ -135,7 +140,10 @@ pub fn convert_movie_with_imports(
             Some(n) if seen.insert(n.to_string()) => n.to_string(),
             _ => continue, // unnamed, or already converted
         };
-        let file = apt::AptFile::load(&base)?;
+        let file = apt::AptFile::load(&base).map_err(|source| Error::LoadMovie {
+            base: base.clone(),
+            source,
+        })?;
         if !options.inline_imports {
             for import in &file.movie.imports {
                 if !seen.contains(&import.movie) {

crates/apt/src/error.rs

@@ -1,10 +1,24 @@
+use std::path::PathBuf;
+
 use thiserror::Error;
 
 #[derive(Debug, Error)]
 pub enum Error {
     #[error("io error: {0}")]
     Io(#[from] std::io::Error),
 
+    #[error("reading {}: {source}", path.display())]
+    ReadFile {
+        path: PathBuf,
+        source: std::io::Error,
+    },
+
+    #[error("parsing APT movie {}: {source}", base.display())]
+    Parse {
+        base: PathBuf,
+        source: Box<Error>,
+    },
+
     #[error("not an APT file: bad header tag")]
     BadAptTag,
 

crates/apt/src/lib.rs

@@ -52,9 +52,20 @@ impl AptFile {
     /// Load from `<base>.apt` + `<base>.const`. `path` may be either file or the base name.
     pub fn load(path: &Path) -> Result<AptFile> {
         let base = base_path(path);
-        let apt_data = std::fs::read(base.with_extension("apt"))?;
-        let const_data = std::fs::read(base.with_extension("const"))?;
-        Self::read(&apt_data, &const_data)
+        let apt_path = base.with_extension("apt");
+        let const_path = base.with_extension("const");
+        let apt_data = std::fs::read(&apt_path).map_err(|source| Error::ReadFile {
+            path: apt_path,
+            source,
+        })?;
+        let const_data = std::fs::read(&const_path).map_err(|source| Error::ReadFile {
+            path: const_path,
+            source,
+        })?;
+        Self::read(&apt_data, &const_data).map_err(|source| Error::Parse {
+            base,
+            source: Box::new(source),
+        })
     }
 }