Render errors cleanly for both CLIs and structured logs#28
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ezekiel-alexrod
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Error() (and the %s/%q verbs) is the message form: it feeds CLI output, %w chains and any logger that prints err.Error(). Baking the stack into it left no way to get the plain message and produced noisy "... at=[(func='...', file='...', line='...')]" tails wherever an error was shown to a human. Error() now carries only title, identifier, details, properties and cause. The full message-plus-stack dump stays available through the %+v verb (unchanged). The "(identifier)" segment is also omitted when no identifier is set, so untyped errors read "title: detail" instead of "title (): detail". Note: this changes the string returned by Error(); callers that parsed it for the stack must switch to %+v.
slog's handlers serialise an error value differently: the JSON handler
falls back to err.Error() (a string) while the text handler uses %+v
(JSON). Combined with go-errors' formatting that inverts the output —
text logs show JSON, JSON logs show the bare message.
Implement slog.LogValuer on *Error so both handlers resolve the same
structured group: title, identifier, details, properties, cause and the
stack. JSON consumers get queryable fields (the stack as an array of
{function,file,line} objects); the text handler renders each frame via
the new Trace.String(), so the stack reads as "<func> <file>:<line>"
instead of pointer addresses.
The stack is part of the log form (post-mortem debugging) but stays out
of Error() (the human/CLI form): the two audiences are served on purpose.
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anthony-treuillier-scality
approved these changes
Jun 4, 2026
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Error() baked the stack trace into its output, so every human-facing error (CLI, %w chains, err.Error() logs) carried a noisy at=[(func=..., file=..., line=...)] tail — with no way to get the plain message. And under slog the two handlers disagreed: the JSON handler falls back to Error() while the text handler uses %+v, so text logs printed JSON and JSON logs printed the bare string.
This PR splits the two audiences cleanly: