Merge pull request #21553 from geoffw0/implicitfn

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

Author: geoffw0

cpp/ql/src/Likely Bugs/Underspecified Functions/ImplicitFunctionDeclaration.qhelp

@@ -14,6 +14,9 @@ function may behave unpredictably.</p>
 <p>This may indicate a misspelled function name, or that the required header containing
 the function declaration has not been included.</p>
 
+<p>Note: This query is not compatible with <code>build mode: none</code> databases, and produces
+no results on those databases.</p>
+
 </overview>
 <recommendation>
 <p>Provide an explicit declaration of the function before invoking it.</p>
@@ -26,4 +29,4 @@ the function declaration has not been included.</p>
 <references>
 <li>SEI CERT C Coding Standard: <a href="https://wiki.sei.cmu.edu/confluence/display/c/DCL31-C.+Declare+identifiers+before+using+them">DCL31-C. Declare identifiers before using them</a></li>
 </references>
-</qhelp>
+</qhelp>

cpp/ql/src/Likely Bugs/Underspecified Functions/ImplicitFunctionDeclaration.ql

@@ -5,7 +5,7 @@
  * may lead to unpredictable behavior.
  * @kind problem
  * @problem.severity warning
- * @precision medium
+ * @precision high
  * @id cpp/implicit-function-declaration
  * @tags correctness
  *       maintainability
@@ -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 produces
+ * no results on those databases.
+ */
+
 predicate locInfo(Locatable e, File file, int line, int col) {
   e.getFile() = file and
   e.getLocation().getStartLine() = line and
@@ -39,6 +44,7 @@ predicate isCompiledAsC(File f) {
 from FunctionDeclarationEntry fdeIm, FunctionCall fc
 where
   isCompiledAsC(fdeIm.getFile()) and
+  not any(Compilation c).buildModeNone() and
   not isFromMacroDefinition(fc) and
   fdeIm.isImplicit() and
   sameLocation(fdeIm, fc) and

cpp/ql/src/change-notes/2026-03-23-implicit-function-declaration.md

@@ -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.

cpp/ql/src/change-notes/2026-04-02-implicit-function-declaration.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The "Implicit function declaration" (`cpp/implicit-function-declaration`) query has been upgraded to `high` precision.