swiftlang/swift

[SR-978] Warn on do {} with only one empty catch {} block

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#43,590 opened on Mar 18, 2016

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compilerdiagnostics qualitydo catchgood first issueimprovementmissing warningstatementsswift 5.9

Description
Previous ID SR-978
Radar None
Original Reporter @jckarter
Type Improvement
Votes 0
Component/s Compiler
Labels Improvement, StarterBug
Assignee MultiColourPixel (JIRA)
Priority Medium

md5: d5f41243d2aaf067f1ecd57198c44970

Issue Description:

Eric Knapp caught some sample code in the wild unwisely using an empty catch block to swallow errors:

https://twitter.com/ejknapp/status/710589235464523776

We should warn on this to encourage people to use try! to trap on unexpected errors instead.

Contributor guide

Tech stack
swift
Domain
developer experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
understanding of Swift syntaxbasic compiler diagnostics knowledge
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
The issue requests a warning for `do {} catch {}` blocks where the catch block is empty (i.e., only one empty catch block). To implement this, you need to add a diagnostic in the Swift compiler's semantic analysis phase. Look at existing warnings like 'unused variable' or 'redundant pattern' in the Swift compiler source (likely under `lib/Sema/` or `include/swift/AST/Diagnostics*`). The issue has a JIRA reference but no code changes yet. Check the comments for any prior discussion or proposed implementation details. The goal is to emit a warning when a catch clause is empty, encouraging use of `try!` instead.