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C++: Ignore compiler-generated variables in unused-static-variable query #22961

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Merged
jketema merged 2 commits into from
Oct 30, 2026
Merged

C++: Ignore compiler-generated variables in unused-static-variable query #22961

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b43b7c3
Add empty parameter pack regression test
jketema Oct 30, 2026
a5e0a2d
Ignore compiler-generated unused static variables
jketema Oct 30, 2026
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1 change: 1 addition & 0 deletions cpp/ql/src/Best Practices/Unused Entities/UnusedStaticVariables.ql
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Expand Up @@ -22,6 +22,7 @@ predicate declarationHasSideEffects(Variable v) {
from Variable v
where
v.isStatic() and
not v.isCompilerGenerated() and
v.hasDefinition() and
not v.isConstexpr() and
not exists(VariableAccess a | a.getTarget() = v) and
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4 changes: 4 additions & 0 deletions cpp/ql/src/change-notes/2026-10-30-unused-static-compiler-generated.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* The `cpp/unused-static-variable` query no longer reports compiler-generated variables, such as placeholders for empty function parameter packs.
9 changes: 8 additions & 1 deletion cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp
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@@ -1,4 +1,4 @@
// semmle-extractor-options: -std=c++17
// semmle-extractor-options: -std=c++20
int globalVar; // GOOD (not static)
static int staticVar1; // GOOD (used)
static int staticVar2; // GOOD (used)
Expand Down Expand Up @@ -49,3 +49,10 @@ struct WithDestructor

static WithConstructor constructed; // GOOD (constructor has a side effect)
static WithDestructor destructed; // GOOD (destructor has a side effect)

static auto sum(auto... values)
{
return (0 + ... + values);
}

int globalVar2 = sum() + sum(2);
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