cpp: silently allow conditional directives within a macro

The presence of preprocessor directives within the arguments
of a macro invocation is Undefined Behaviour [6.10.3p11].
However, conditional directives are harmless here and are
useful (and commonly used in the kernel).

So, relax the warning by restricting it to non-conditional
directives.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>

3 files changed, 55 insertions, 4 deletions

diff --git a/pre-process.c b/pre-process.c
index 82bfa402..a5a3c5fb 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -48,6 +48,7 @@ static struct ident_list *macros;	// only needed for -dD
 static int false_nesting = 0;
 static int counter_macro = 0;		// __COUNTER__ expansion
 static int include_level = 0;
+static int expanding = 0;
 
 #define INCLUDEPATHS 300
 const char *includepath[INCLUDEPATHS+1] = {
@@ -232,8 +233,13 @@ static int expand_one_symbol(struct token **list)
 		sym->expander(token);
 		return 1;
 	} else {
+		int rc;
+
 		sym->used_in = file_scope;
-		return expand(list, sym);
+		expanding = 1;
+		rc = expand(list, sym);
+		expanding = 0;
+		return rc;
 	}
 }
 
@@ -271,8 +277,6 @@ static struct token *collect_arg(struct token *prev, int vararg, struct position
 	while (!eof_token(next = scan_next(p))) {
 		if (next->pos.newline && match_op(next, '#')) {
 			if (!next->pos.noexpand) {
-				warning(next->pos,
-					     "directive in macro's argument list");
 				preprocessor_line(stream, p);
 				__free_token(next);	/* Free the '#' token */
 				continue;
@@ -2073,6 +2077,7 @@ static void handle_preprocessor_line(struct stream *stream, struct token **line,
 	int (*handler)(struct stream *, struct token **, struct token *);
 	struct token *token = start->next;
 	int is_normal = 1;
+	int is_cond = 0;	// is one of {is,ifdef,ifndef,elif,else,endif}
 
 	if (eof_token(token))
 		return;
@@ -2082,6 +2087,7 @@ static void handle_preprocessor_line(struct stream *stream, struct token **line,
 		if (sym) {
 			handler = sym->handler;
 			is_normal = sym->normal;
+			is_cond = !sym->normal;
 		} else {
 			handler = handle_nondirective;
 		}
@@ -2096,6 +2102,11 @@ static void handle_preprocessor_line(struct stream *stream, struct token **line,
 		if (false_nesting)
 			goto out;
 	}
+
+	if (expanding) {
+		if (!is_cond || Wpedantic)
+			warning(start->pos, "directive in macro's argument list");
+	}
 	if (!handler(stream, line, token))	/* all set */
 		return;
 
diff --git a/validation/preprocessor/directive-within-macro.c b/validation/preprocessor/directive-within-macro.c
new file mode 100644
index 00000000..5269d4a7
--- /dev/null
+++ b/validation/preprocessor/directive-within-macro.c
@@ -0,0 +1,40 @@
+#define f(x) x
+
+f(1
+#if 1		// OK
+  a
+#elif 2		// OK
+  b
+#else		// OK
+  c
+#endif		// OK
+#ifdef f	// OK
+  d
+#endif		// OK
+#ifndef f	// OK
+  e
+#endif		// OK
+  3)
+
+f(1
+#define x y	// KO
+  3)
+
+/*
+ * check-name: directive-within-macro
+ * check-command: sparse -E $file
+ *
+ * check-output-start
+
+1
+a
+d
+3
+1
+3
+ * check-output-end
+ *
+ * check-error-start
+preprocessor/directive-within-macro.c:20:1: warning: directive in macro's argument list
+ * check-error-end
+ */
diff --git a/validation/preprocessor/preprocessor22.c b/validation/preprocessor/preprocessor22.c
index 277334c6..11f625c0 100644
--- a/validation/preprocessor/preprocessor22.c
+++ b/validation/preprocessor/preprocessor22.c
@@ -17,7 +17,7 @@ define_struct(a, {
  * check-description: Directives are not allowed within a macro argument list,
  * although cpp deals with it to treat macro more like C functions.
  *
- * check-command: sparse -E $file
+ * check-command: sparse -pedantic -E $file
  *
  * check-error-start
 preprocessor/preprocessor22.c:6:1: warning: directive in macro's argument list