C++: Don't report results in files with compilation errors.

cpp/ql/src/Best Practices/Unused Entities/UnusedStaticFunctions.ql

@@ -14,15 +14,28 @@
 import cpp
 
 predicate immediatelyReachableFunction(Function f) {
-  not f.isStatic() or
-  exists(BlockExpr be | be.getFunction() = f) or
-  f instanceof MemberFunction or
-  f instanceof TemplateFunction or
-  f.getFile() instanceof HeaderFile or
-  f.getAnAttribute().hasName("constructor") or
-  f.getAnAttribute().hasName("destructor") or
-  f.getAnAttribute().hasName("used") or
+  not f.isStatic()
+  or
+  exists(BlockExpr be | be.getFunction() = f)
+  or
+  f instanceof MemberFunction
+  or
+  f instanceof TemplateFunction
+  or
+  f.getFile() instanceof HeaderFile
+  or
+  f.getAnAttribute().hasName("constructor")
+  or
+  f.getAnAttribute().hasName("destructor")
+  or
+  f.getAnAttribute().hasName("used")
+  or
   f.getAnAttribute().hasName("unused")
+  or
+  // a compiler error in the same file suggests we may be missing data
+  exists(Diagnostic d | d.getFile() = f.getFile() and d.getSeverity() >= 3)
+  or
+  exists(ErrorExpr ee | ee.getFile() = f.getFile())
 }
 
 predicate immediatelyReachableVariable(Variable v) {

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticFunctions/UnusedStaticFunctions.expected

@@ -1,5 +1,3 @@
-| extraction_error.c:4:13:4:43 | my_function2_called_after_error | Static function my_function2_called_after_error is unreachable | extraction_error.c:4:13:4:43 | my_function2_called_after_error | my_function2_called_after_error |
-| extraction_error.c:5:13:5:35 | my_function3_not_called | Static function my_function3_not_called is unreachable | extraction_error.c:5:13:5:35 | my_function3_not_called | my_function3_not_called |
 | unused_functions.c:16:13:16:27 | unused_function | Static function unused_function is unreachable | unused_functions.c:16:13:16:27 | unused_function | unused_function |
 | unused_functions.c:20:13:20:28 | unused_function2 | Static function unused_function2 is unreachable ($@ must be removed at the same time) | unused_functions.c:24:13:24:28 | unused_function3 | unused_function3 |
 | unused_functions.c:24:13:24:28 | unused_function3 | Static function unused_function3 is unreachable | unused_functions.c:24:13:24:28 | unused_function3 | unused_function3 |

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticFunctions/extraction_error.c

@@ -1,8 +1,8 @@
 // semmle-extractor-options: --expect_errors
 
 static void my_function1_called() {} // GOOD
-static void my_function2_called_after_error() {} // GOOD [FALSE POSITIVE]
-static void my_function3_not_called() {} // BAD
+static void my_function2_called_after_error() {} // GOOD
+static void my_function3_not_called() {} // BAD [NOT DETECTED]
 
 int main(void) {
 	my_function1_called();