C++: Make node.asExpr() instanceof ClassAggregateLiteral satisfiable
#19501
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… instanceof ClassAggregateLiteral' holds for this new node subclass.
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Pull Request Overview
This PR enables node.asExpr() instanceof ClassAggregateLiteral by mapping the final post-update node of a class aggregate initialization back to its aggregate literal, and updates tests and change notes accordingly.
- Introduces
ClassAggregateInitializerPostUpdateNodeand related predicates inExprNodes.qllto link post-update nodes toClassAggregateLiteral. - Updates existing IR-based dataflow tests to expect
{...}nodes for class aggregate literals. - Adds new test cases in
asExpr/test.cppfor class aggregate literal expressions and documents missing support for array aggregates.
Reviewed Changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| cpp/ql/test/library-tests/dataflow/fields/ir-path-flow.expected | Swapped out post-update labels for {...} to reflect the class aggregate literal. |
| cpp/ql/test/library-tests/dataflow/dataflow-tests/localFlow-ir.expected | Inserted {...} expectation for class aggregate literal in local flow tests. |
| cpp/ql/test/library-tests/dataflow/asExpr/test.cpp | Added asExpr={...} checks for struct aggregate literals; marked missing for arrays. |
| cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/ExprNodes.qll | Implemented post-update mapping for ClassAggregateLiteral and extended expr nodes. |
| cpp/ql/lib/change-notes/2025-05-15-class-aggregate-literals.md | Documented the fix for asExpr() on class aggregate literals. |
| * ``` | ||
| * i.getUnconvertedResultExpression() instanceof ClassAggregateLiteral | ||
| * ``` | ||
| * and thus we don't automaticallt get a dataflow node for which: |
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Typo in comment: change 'automaticallt' to 'automatically'.
Suggested change
| * and thus we don't automaticallt get a dataflow node for which: | |
| * and thus we don't automatically get a dataflow node for which: |
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| @@ -442,6 +478,12 @@ private module Cached { | |||
| final override Expr getConvertedExpr(int n) { exprNodeShouldBeIndirectOperand(this, result, n) } | |||
| } | |||
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| private class PostUpdateExprNode extends ExprNodeBase instanceof PostUpdateNode { | |||
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QL class declarations list superclasses and interfaces separated by commas. Replace 'extends ExprNodeBase instanceof PostUpdateNode' with 'extends ExprNodeBase, PostUpdateNode' to correctly inherit both.
Suggested change
| private class PostUpdateExprNode extends ExprNodeBase instanceof PostUpdateNode { | |
| private class PostUpdateExprNode extends ExprNodeBase, PostUpdateNode { |
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The C++ IR represents an aggregate literal
x = {.a = 1, .b = 2}as a sequence of field writes:and as such there is no instruction for which
getUnconvertedResultExpression()gives the aggregate literal. And sinceNode.asExpr()piggybacks ongetUnconvertedResultExpression()for most nodesnode.asExpr() instanceof AggregateLiteralalso never holds. This gotcha has bitten users several times.This PR solves the problem for class aggregate literals. Since class aggregate literals are represented as a sequence of field writes (see above), we can pick the last field write's post-update node as the node to represent the aggregate literal expression. Semantically this makes sense since the last post-update node represents the state of the object after the last field has been initialized.
Sadly, since we don't model array writes using post-update nodes we can't use the same trick for
ArrayAggregateLiterals. However, I think we should do that eventually. Once we do that we can apply a similar trick to that case. For now I think this solution at least solves half of the problems that's been reported.