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

1 files changed, 4 insertions, 2 deletions

diff --git a/subplot.md b/subplot.md
index 6a268f7..f99b326 100644
--- a/subplot.md
+++ b/subplot.md
@@ -2399,7 +2399,8 @@ given file missing-binding.md
 and an installed subplot
 when I try to run subplot docgen missing-binding.md -o foo.html
 then command fails
-and stderr contains ": missing-binding.yaml:"
+and stderr contains "could not be found"
+and stderr contains "missing-binding.yaml"
 ~~~
 
 ~~~{#missing-binding.md .file .markdown .numberLines}
@@ -2420,7 +2421,8 @@ and file b.yaml
 and an installed subplot
 when I try to run subplot codegen --run missing-functions.md -o foo.py
 then command fails
-and stderr contains ": missing-functions.py:"
+and stderr contains "could not be found"
+and stderr contains "missing-functions.py"
 ~~~
 
 ~~~{#missing-functions.md .file .markdown .numberLines}