C#: Improve dataflow for mutation definition and mutation operator calls.#21839
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michaelnebel wants to merge 6 commits into
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C#: Improve dataflow for mutation definition and mutation operator calls.#21839michaelnebel wants to merge 6 commits into
michaelnebel wants to merge 6 commits into
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…ount for implicit assignment of built and user-definied static operator calls.
…d decrement (only use the specialized code, which is already present).
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Pull request overview
This PR updates the C# dataflow/SSA modeling around mutation operations (++, --) and mutator operator calls, and refreshes the affected library-test baselines accordingly.
Changes:
- Extend assignable/mutation definition handling to cover additional mutation-operator call cases.
- Adjust sign-analysis SSA assignment extraction to avoid treating mutator operations as simple assignments.
- Add/extend operator dataflow library tests and update corresponding
.expectedoutputs.
Show a summary per file
| File | Description |
|---|---|
| csharp/ql/test/library-tests/fields/Fields11.expected | Updated baseline for field-flow expectations impacted by mutation handling. |
| csharp/ql/test/library-tests/dataflow/operators/operatorFlow.expected | Updated operator-flow graph baseline with new mutator operator edges/nodes. |
| csharp/ql/test/library-tests/dataflow/operators/Operator.cs | Adds user-defined decrement operator + new flow assertions for -- scenarios. |
| csharp/ql/test/library-tests/dataflow/local/TaintTrackingStep.expected | Updated baseline to include SSA steps for decrement operations. |
| csharp/ql/test/library-tests/dataflow/local/DataFlowStep.expected | Updated baseline to include dataflow steps for decrement operations. |
| csharp/ql/test/library-tests/csharp7/LocalTaintFlow.expected | Updated baseline for taint steps involving increment operations. |
| csharp/ql/test/library-tests/assignables/GetAnAssignedValue.expected | Updated baseline to treat mutation operations as assigned-value sources. |
| csharp/ql/test/library-tests/assignables/AssignableDefinition.expected | Updated baseline for mutation definitions to record the mutation op as the source. |
| csharp/ql/lib/semmle/code/csharp/dataflow/internal/rangeanalysis/SignAnalysisSpecific.qll | Tweaks SSA-to-expression extraction to exclude mutator-operation defining expressions. |
| csharp/ql/lib/semmle/code/csharp/Assignable.qll | Introduces mutation-operation assignment abstraction and updates mutation-definition plumbing. |
| csharp/ql/lib/change-notes/2026-05-19-mutation-operator-dataflow.md | Adds a change note entry (currently duplicates an existing one). |
Copilot's findings
- Files reviewed: 11/11 changed files
- Comments generated: 3
| var x = new C1(); | ||
| var y = x--; | ||
| Sink(x.Field); // $ hasValueFlow=2 | ||
| Sink(y.Field); // $ hasValueFlow=2 |
| } | ||
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| /** | ||
| * A mutation operation that implicitly assigns the result to its operand. For example, `a++` in |
| --- | ||
| category: minorAnalysis | ||
| --- | ||
| * C# 14: Added support for user-defined instance increment/decrement operators. |
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@hvitved : No need to review this as it shouldn't be merged. |
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In this PR, we improve data-flow for mutation operations and mutator operator calls.
Note, that
c++implicitly (if this is not an instance operator) the resulting value toc.Comments on DCA
cs/invalid-dynamic-call, which is a removal of a false positive (related to a dynamic call of--). However, I believe this is somewhat due to wobliness as there is another PR, which "introduces" a similar result in themonoproject (which is a false positive). I am not able to reproduce with a local example.