The dispatcher's top-level error handler prints `"error: {err}"`,
which is anyhow's bare Display. anyhow's Display only renders the
top-level context message and drops every cause beneath it. Users hit
"failed to parse config at <path>" with zero hint about the actual
TOML error (line/column, expected token, missing quote, BOM, etc.).
This is the gap reported in #767: the OP got
`error: failed to parse config at C:\Users\y1547\.deepseek\config.toml`
with nothing else, while a separate code path that uses a different
formatter shows a rich `Caused by: TOML parse error at line 1, column
20 ...` chain. Maintainer was unable to triage without the underlying
parse error.
Print the full chain by iterating `err.chain().skip(1)` after the
top-level message. Output for the issue's case becomes:
error: failed to parse config at C:\Users\y1547\.deepseek\config.toml
caused by: TOML parse error at line N, column M
| (snippet from toml-rs)
Tests: regression test pins the chain semantics so a future refactor
of the print path can't silently drop causes again.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Hunter Bown
d70bec6ac5