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C++: Disable cpp/implicit-function-declaration on build mode none databases #21553

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C++: Disable cpp/implicit-function-declaration on build mode none databases #21553

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C++: Disable cpp/implicit-function-declaration on BMN databases.
geoffw0 Mar 23, 2026
39056e4
C++: Change note.
geoffw0 Mar 23, 2026
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6 changes: 6 additions & 0 deletions cpp/ql/src/Likely Bugs/Underspecified Functions/ImplicitFunctionDeclaration.ql
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,11 @@ import TooFewArguments
import TooManyArguments
import semmle.code.cpp.commons.Exclusions

/*
* This query is not compatible with build mode: none databases, and has
* no results on those databases.
Comment on lines +21 to +22
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Copilot AI Mar 23, 2026

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The comment states unconditionally that the query “has no results” on build mode: none databases, but that guarantee depends on the correctness of the build-mode detection logic in the where clause. After switching to an exists(...)-style guard (see other comment), consider updating the wording slightly to describe the mechanism (e.g., “Results are suppressed on build mode: none databases”) to avoid overstating the behavior if the guard changes again later.

Suggested change
* This query is not compatible with build mode: none databases, and has
* no results on those databases.
* This query is not compatible with build mode: none databases; results
* are suppressed on such databases by the build-mode guard in the `where` clause.

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*/

predicate locInfo(Locatable e, File file, int line, int col) {
e.getFile() = file and
e.getLocation().getStartLine() = line and
Expand All @@ -39,6 +44,7 @@ predicate isCompiledAsC(File f) {
from FunctionDeclarationEntry fdeIm, FunctionCall fc
where
isCompiledAsC(fdeIm.getFile()) and
not any(Compilation c).buildModeNone() and
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Copilot AI Mar 23, 2026

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any(Compilation c).buildModeNone()is an aggregation that can be ill-defined if there are noCompilationrows (which may be the case in build mode: none / buildless databases). In that scenario, this guard may not evaluate as intended, potentially failing to suppress results (or suppressing everything unexpectedly depending on QL semantics). Prefer a quantifier-based check that behaves correctly on empty sets, e.g.not exists(Compilation c | c.buildModeNone())` (or the project’s canonical “is build mode none” predicate if one exists).

Suggested change
not any(Compilation c).buildModeNone() and
exists(Compilation c | not c.buildModeNone()) and

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not isFromMacroDefinition(fc) and
fdeIm.isImplicit() and
sameLocation(fdeIm, fc) and
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4 changes: 4 additions & 0 deletions cpp/ql/src/change-notes/2026-03-23-implicit-function-declaration.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* The "Implicit function declaration" (`cpp/implicit-function-declaration`) query no longer produces results on `build mode: none` databases. These results were found to be very noisy and fundamentally imprecise in this mode.
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