C++: Add heuristics for meson configuration files

cpp/ql/lib/change-notes/2026-03-31-meson.md

@@ -0,0 +1,5 @@
+
+---
+category: feature
+---
+* Added subclass `MesonPrivateTestFile` of `ConfigurationTestFile` that represents files created by Meson to test the build configuration.

cpp/ql/lib/semmle/code/cpp/ConfigurationTestFile.qll

@@ -26,3 +26,19 @@ class CmakeTryCompileFile extends ConfigurationTestFile {
     )
   }
 }
+
+/**
+ * A file created by Meson to test the system configuration.
+ */
+class MesonPrivateTestFile extends ConfigurationTestFile {
+  MesonPrivateTestFile() {
+    this.getBaseName() = "testfile.c" and
+    exists(Folder folder, Folder parent |
+      folder = this.getParentContainer() and
+      parent = folder.getParentContainer()
+    |
+      folder.getBaseName().matches("tmp%") and
+      parent.getBaseName() = "meson-private"
+    )
+  }
+}

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/ExprHasNoEffect/meson-private/tmp_abc/ExprHasNoEffect.qlref

@@ -0,0 +1 @@
+Likely Bugs/Likely Typos/ExprHasNoEffect.ql

cpp/ql/test/query-tests/Likely Bugs/Likely Typos/ExprHasNoEffect/meson-private/tmp_abc/testfile.c

@@ -0,0 +1,8 @@
+typedef long long size_t;
+
+size_t strlen(const char *s);
+
+int main() {
+  strlen(""); // GOOD: the source file occurs in a `meson-private/tmp.../testfile.c` directory
+  return 0;
+}