CPP: Better fileHeaderLimit.

Author: geoffw0

cpp/ql/src/semmle/code/cpp/AutogeneratedFile.qll

@@ -48,14 +48,45 @@ predicate hasPragmaDifferentFile(File f) {
 }
 
 /**
- * The maximum line number we consider to be "near the beginning" of file `f`.
+ * The line where the first comment in file `f` begins (maximum of 5).  This allows
+ * us to skip past any preprocessor logic or similar code before the first comment.
+ */
+private int fileFirstComment(File f) {
+  result = min(int line |
+    exists(Comment c |
+      c.getFile() = f and
+      c.getLocation().getStartLine() = line and
+      line < 5
+    )
+  ).minimum(5)
+}
+
+/**
+ * The line where the initial comments of file `f` end.  This is just before the
+ * first bit of code, excluding anything skipped over by `fileFirstComment`.
  */
 private int fileHeaderLimit(File f) {
-  result = max(int head, int line |
-    head <= 5 and
-    locations_default(_, underlyingElement(f), head, _, line, _) |
-    line
-  ) + 5
+  exists(int fc |
+    fc = fileFirstComment(f) and
+    result = min(int line |
+      exists(DeclarationEntry de, Location l |
+        l = de.getLocation() and
+        l.getFile() = f and
+        line = l.getStartLine() - 1 and
+        line > fc
+      ) or exists(PreprocessorDirective pd, Location l |
+        l = pd.getLocation() and
+        l.getFile() = f and
+        line = l.getStartLine() - 1 and
+        line > fc
+      ) or exists(NamespaceDeclarationEntry nde, Location l |
+        l = nde.getLocation() and
+        l.getFile() = f and
+        line = l.getStartLine() - 1 and
+        line > fc
+      ) or line = f.getMetrics().getNumberOfLines()
+    )
+  )
 }
 
 /**
@@ -69,10 +100,13 @@ private int fileHeaderLimit(File f) {
  */
 class AutogeneratedFile extends File {
   cached AutogeneratedFile() {
-    exists(Comment c |
-      c.getFile() = this and
-      c.getLocation().getStartLine() <= fileHeaderLimit(this) and
-      autogeneratedComment(c)
-    ) or hasPragmaDifferentFile(this)
+    autogeneratedComment(
+      concat(Comment c |
+        c.getFile() = this and
+        c.getLocation().getStartLine() <= fileHeaderLimit(this) |
+        c.getContents() order by c.getLocation().getStartLine()
+      )
+    ) or
+    hasPragmaDifferentFile(this)
   }
 }