feat: make errors have a source error

When errors have a source, i.e., an underlying error, it results in
better error messages to the user.

Also, refactor the way the source chain is printed, to code that is
clearer to me.

I will need this to for loading document metadata from an external
YAML file.

Sponsored-by: author

2 files changed, 16 insertions, 15 deletions

diff --git a/src/bin/subplot.rs b/src/bin/subplot.rs
index e9cb00a..5e802b4 100644
--- a/src/bin/subplot.rs
+++ b/src/bin/subplot.rs
@@ -504,13 +504,6 @@ fn load_linted_doc(
     Ok(doc)
 }
 
-fn print_source_errors(e: Option<&dyn std::error::Error>) {
-    if let Some(e) = e {
-        error!("{}", e);
-        print_source_errors(e.source());
-    }
-}
-
 fn real_main() {
     info!("Starting Subplot");
     let argparser = Toplevel::command();
@@ -525,7 +518,11 @@ fn real_main() {
         }
         Err(e) => {
             error!("{}", e);
-            print_source_errors(e.source());
+            let mut e = e.source();
+            while let Some(source) = e {
+                error!("caused by: {}", source);
+                e = source.source();
+            }
             process::exit(1);
         }
     }
diff --git a/src/error.rs b/src/error.rs
index a42298d..d714d21 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -13,12 +13,12 @@ pub enum SubplotError {
     Warnings(usize),
 
     /// Subplot could not find a file named as a bindings file.
-    #[error("binding file could not be found: {0}: {1}")]
-    BindingsFileNotFound(PathBuf, std::io::Error),
+    #[error("binding file could not be found: {0}")]
+    BindingsFileNotFound(PathBuf, #[source] std::io::Error),
 
     /// Subplot could not find a file named as a functions file.
-    #[error("functions file could not be found: {0}: {1}")]
-    FunctionsFileNotFound(PathBuf, std::io::Error),
+    #[error("functions file could not be found: {0}")]
+    FunctionsFileNotFound(PathBuf, #[source] std::io::Error),
 
     /// The simple pattern specifies a kind that is unknown.
     #[error("simple pattern kind {0} is unknown")]
@@ -201,7 +201,7 @@ pub enum SubplotError {
     ///
     /// The `add-newline` attribute can only take the values `auto`, `yes`,
     /// and `no`.
-    #[error("Embedded file {0} has unrecognised `add-newline={}` - valid values are auto/yes/no")]
+    #[error("Embedded file {0} has unrecognised `add-newline={1}` - valid values are auto/yes/no")]
     UnrecognisedAddNewline(String, String),
 
     /// Couldn't determine base directory from input file name.
@@ -233,8 +233,8 @@ pub enum SubplotError {
     NoTemplateSpecDirectory(PathBuf),
 
     /// A code template has an error.
-    #[error("Couldn't load template {0}: {1}")]
-    TemplateError(String, tera::Error),
+    #[error("Couldn't load template {0}")]
+    TemplateError(String, #[source] tera::Error),
 
     /// Unknown classes in use in document
     #[error("Unknown classes found in the document: {0}")]
@@ -302,6 +302,10 @@ pub enum SubplotError {
     #[error("Failed to parse YAML metadata")]
     Metadata(#[source] serde_yaml::Error),
 
+    /// Error parsing YAML metadata for document, from external file.
+    #[error("Failed to parse YAML metadata in {0}")]
+    MetadataFile(PathBuf, #[source] serde_yaml::Error),
+
     /// Abstract syntax tree error.
     #[error(transparent)]
     Ast(#[from] crate::ast::Error),