[SkyCipherr]

Summary

Related to #15028.

Add a format-specifier suggestion to existing cpp/wrong-type-format-argument alerts for simple decimal integer conversions. For example, a %d conversion with an unsigned long argument on LP64 now suggests %lu.

The suggestion uses the argument type after default argument promotions and distinguishes int, long, and long long, including unsigned variants. It retains i for signed i conversions and uses u for unsigned arguments. The detection predicates and existing message text are unchanged; suggestions are appended only to conversion-value arguments.

This intentionally covers only plain %d, %i, %u, and their l/ll forms. Flags, width, precision, positional arguments, non-decimal conversions, and other types retain their existing messages. It does not attempt to close the full issue or change the existing treatment of equal-width integer types.

Validation

Validated with CodeQL CLI 2.27.4 against main at fbf9fca5ce7c3b64c2f5d719ea0444577850cb4a:

• All 12 existing tests and 2 new Linux/Microsoft target-model tests pass (14/14).
• Across all 14 test result files, result counts, locations, and original messages are unchanged after removing the suggestion suffixes.
• A separate database extracted through real MinGW-w64 GCC 16.1.0 compilation has the same 19 alerts before and after; 10 gain suggestions. This LLP64 database uses long long cases because the issue's unsigned long versus int example is equal-width and is not reported by the existing query on that target. The original example is covered by the Linux target-model test.
• The 10 suggested replacements from that database, plus the original example's %lu replacement, pass GCC -Wformat=2 -Werror=format compilation checks. Mismatched calls were not executed.
• QL compilation, QL formatting, and git diff --check pass.

The full repository suite and large-project evaluation were not run. Upstream CI has not yet run for this change.

[Copilot]

🟡 Changes recommended

The production-query change lacks the repository’s broader DCA evaluation to check for unexpected diagnostic regressions beyond the focused tests and MinGW database.

1 open issue

• Run the broader DCA evaluation for the production-query change · New

What changed in this PR

Adds format-specifier suggestions to the C++ cpp/wrong-type-format-argument query, partially addressing #15028 without changing mismatch detection.

Changes:

• Suggests matching specifiers for plain decimal integer conversions using promoted argument types.
• Adds Linux and Microsoft target-model tests covering suggestions and excluded cases.
• Updates existing expected diagnostics and adds a release note.

File	Description
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​WrongTypeFormatArguments/​Microsoft/​WrongTypeFormatArguments.expected	Updates Microsoft diagnostic expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​WrongTypeFormatArguments/​Microsoft_no_wchar/​WrongTypeFormatArguments.expected	Updates no-wchar diagnostic expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​WrongTypeFormatArguments/​Linux_unsigned_chars/​WrongTypeFormatArguments.expected	Updates unsigned-char diagnostic expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​WrongTypeFormatArguments/​Linux_signed_chars/​WrongTypeFormatArguments.expected	Updates signed-char diagnostic expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​WrongTypeFormatArguments/​Buildless/​WrongTypeFormatArguments.expected	Updates buildless diagnostic expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Microsoft/​WrongTypeFormatArguments.qlref	Connects Microsoft tests to the query.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Microsoft/​WrongTypeFormatArguments.expected	Records Microsoft suggestion expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Microsoft/​options	Configures the Microsoft target model.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Microsoft/​integer-hints.c	Adds Microsoft suggestion and exclusion cases.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Linux/​WrongTypeFormatArguments.qlref	Connects Linux tests to the query.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Linux/​WrongTypeFormatArguments.expected	Records Linux suggestion expectations.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Linux/​options	Configures the Linux test extractor.
cpp/​ql/​test/​query-tests/​Likely Bugs/​Format/​IntegerFormatSuggestions/​Linux/​integer-hints.c	Adds Linux suggestion and exclusion cases.
cpp/​ql/​src/​Likely Bugs/​Format/​WrongTypeFormatArguments.ql	Appends suggestions for supported integer mismatches.
cpp/​ql/​src/​change-notes/​2026-11-12-integer-format-suggestions.md	Documents the diagnostic enhancement.

_{Review effort: Balanced (auto)}

[jketema]

This feels very hacky. I think a more principled approach would likely be to update cpp/ql/lib/semmle/code/cpp/commons/Printf.qll to provide this information.

[SkyCipherr]

Thanks @jketema. Following your suggestion, I've reworked this in 0dc2c48.

Printf.qll now exposes FormatLiteral.getSuggestedIntegerConversionSpecifier(int n, Type type). It uses the existing parseConvSpec fields and the supplied promoted argument type to provide the replacement specifier. The query no longer has its own type-to-specifier mapping or regular-expression check; it only checks that the diagnostic concerns the conversion-value argument and formats the suggestion message. The alert detection predicates are unchanged.

The API is deliberately limited to the existing scope: plain decimal d, i, and u conversions with optional l or ll, for signed/unsigned int, long, and long long types. It preserves i for signed arguments and has no result for unsupported types, flags, width, precision, positional parameters, or other conversions. Its documentation states that callers supply the type after default argument promotions; it provides specifier information independently of whether a mismatch is reported. I've also added a library feature change note.

Validation with CodeQL CLI 2.27.4:

• All 20 relevant tests pass: the 14 existing PR query tests, 4 existing printf library tests, and 2 new direct API tests.
• Each new Linux/Microsoft API test checks 61 conversion positions: 27 supported and 34 excluded. These cover type categories independent of ABI widths, signedness, i preservation, typedefs/qualifiers, raw versus promoted narrow types, per-conversion mapping, decorators, positional parameters, and malformed/unsupported formats.
• All 14 existing query result files are unchanged, including locations and complete messages.
• Reanalysis of the existing real-GCC reproducer still produces the same 19 alerts and 10 suggestions, with identical messages and locations.
• The 26 corrected calls from the new library fixtures and the previous 11 corrected calls pass GCC -Wformat=2 -Werror=format compilation checks. Mismatched calls were not executed.
• QL compilation, formatting, and git diff --check pass.

These are local validation results. I have not run the full repository suite or refreshed upstream DCA for this commit; it still needs upstream CI/DCA.