Implement Rule 22-4-1, only assign literal 0 to errno.#987
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MichaelRFairhurst merged 3 commits intomainfrom Dec 4, 2025
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Pull request overview
This PR implements MISRA C++ 2023 Rule 22-4-1, which requires that only the literal value zero should be assigned to errno. The rule aims to discourage the use of errno for error handling in C++ projects, as modern C++ provides better alternatives.
Key Changes:
- Added a new CodeQL query to detect invalid assignments to errno (non-zero values, expressions, variables, or compound assignments)
- Created supporting library for errno detection and integrated it with the existing literals framework
- Added comprehensive test cases covering various assignment scenarios including literals, macros, expressions, and casts
Reviewed changes
Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| rules.csv | Added Rule 22-4-1 entry with Preconditions4 package reference |
| rule_packages/cpp/Preconditions4.json | Rule package metadata for the new errno assignment query |
| cpp/misra/src/rules/RULE-22-4-1/InvalidAssignmentToErrno.ql | Main query implementation detecting invalid errno assignments |
| cpp/common/src/codingstandards/cpp/standardlibrary/Errno.qll | Library for identifying errno variable accesses |
| cpp/common/src/codingstandards/cpp/exclusions/cpp/Preconditions4.qll | Query metadata and exclusion support for the rule package |
| cpp/common/src/codingstandards/cpp/exclusions/cpp/RuleMetadata.qll | Integration of Preconditions4 package into metadata system |
| cpp/misra/test/rules/RULE-22-4-1/test.cpp | Comprehensive test cases for compliant and non-compliant errno usage |
| cpp/misra/test/rules/RULE-22-4-1/InvalidAssignmentToErrno.qlref | Test query reference |
| cpp/misra/test/rules/RULE-22-4-1/InvalidAssignmentToErrno.expected | Expected test results |
| cpp/common/test/includes/standard-library/errno.h | Added standard error macro definitions for testing |
| cpp/common/test/includes/standard-library/string | Added empty() method to basic_string for test completeness |
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mbaluda
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Nov 25, 2025
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mbaluda
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mbaluda
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Suggested minor improvement to the error message
…conditions-rule-22-4-1-literal-value-0-errno
MichaelRFairhurst
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michaelrfairhurst/preconditions-rule-22-4-1-literal-value-0-errno
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Description
Implement Rule 22-4-1, only assign literal 0 to errno.
Change request type
.ql,.qll,.qlsor unit tests)Rules with added or modified queries
Release change checklist
A change note (development_handbook.md#change-notes) is required for any pull request which modifies:
If you are only adding new rule queries, a change note is not required.
Author: Is a change note required?
🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.
Reviewer: Confirm that either a change note is not required or the change note is required and has been added.
Query development review checklist
For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:
Author
As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
Reviewer
As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.