Narrow Catch Skips Promised Fallback

What goes wrong

A 'return the input unchanged on bad data' fallback catches only the exception types someone listed from a parser call, so an unlisted exception from the same call escapes the fallback and one bad item aborts the whole batch.

Example

The per-row date parser's fallback catches only the bad-value error; one row raises a wrong-type error and the whole 10,000-row import dies instead of skipping that row.

Not to be confused with

The catch is too narrow for the operation it guards; not a swallowed cancellation (Swallowed Cancellation) and not error details thrown away (Discarded Failure Diagnostics).

Discovered by

@sks24git GitHub

Field notes · 4

@sks24git2026-11-03

A fallback for a failed status update caught only the API error class, while a garbled proxy reply raises a sibling class. That error skips the fallback and the user gets no sign the message arrived.

Catch the library's base error in a fallback. A promise of "always" breaks on the one sibling class you did not name.

@sks24git2026-10-27beat 2 review rounds

A daily step catches ordinary exceptions, but the client it calls reports failures by raising a process exit. One bad remote reply after the cutoff hour kills the whole sweeper on every pass.

Know how your helpers fail before you catch. An exit is not an exception, so a bare catch walks past it.
Fake failures the way the real client fails. The wrong type proves nothing.

@sks24git2026-10-27

A per-item loop guarded each item with a catch for ordinary errors, but the CLI wrapper it called signals failure by exiting the process. One bad item ends the whole sweep and every later item is silently skipped.

Know how a dependency fails before you catch around it. A wrapper that exits is not an exception; a narrow catch is a hole.
Copy the sibling's guard, not its shape.

@sks24git2026-10-15

A network call caught only the OS-level error base, but the HTTP client raises its own protocol errors outside that tree. A cut-off reply or a bad status line escaped and aborted the whole scheduler step.

Catch every error family the client raises. Protocol errors often sit outside the OS error tree.
Check input bounds before the first remote call. A cap applied later protects nothing.