[GNU] Add #include_next

preprocess.c

@@ -68,6 +68,7 @@ struct Hideset {
 static HashMap macros;
 static CondIncl *cond_incl;
 static HashMap pragma_once;
+static int include_next_idx;
 
 static Token *preprocess2(Token *tok);
 static Macro *find_macro(Token *tok);
@@ -696,11 +697,21 @@ char *search_include_paths(char *filename) {
     if (!file_exists(path))
       continue;
     hashmap_put(&cache, filename, path);
+    include_next_idx = i + 1;
     return path;
   }
   return NULL;
 }
 
+static char *search_include_next(char *filename) {
+  for (; include_next_idx < include_paths.len; include_next_idx++) {
+    char *path = format("%s/%s", include_paths.data[include_next_idx], filename);
+    if (file_exists(path))
+      return path;
+  }
+  return NULL;
+}
+
 // Read an #include argument.
 static char *read_include_filename(Token **rest, Token *tok, bool *is_dquote) {
   // Pattern 1: #include "foo.h"
@@ -863,6 +874,14 @@ static Token *preprocess2(Token *tok) {
       continue;
     }
 
+    if (equal(tok, "include_next")) {
+      bool ignore;
+      char *filename = read_include_filename(&tok, tok->next, &ignore);
+      char *path = search_include_next(filename);
+      tok = include_file(tok, path ? path : filename, start->next->next);
+      continue;
+    }
+
     if (equal(tok, "define")) {
       read_macro_definition(&tok, tok->next);
       continue;

test/driver.sh

@@ -265,4 +265,13 @@ echo 'int foo(); int bar=3; int main() { foo(); }' > $tmp/main.c
 $chibicc -o $tmp/foo $tmp/main.c $tmp/foo.so
 check -fPIC
 
+# #include_next
+mkdir -p $tmp/next1 $tmp/next2 $tmp/next3
+echo '#include "file1.h"' > $tmp/file.c
+echo '#include_next "file1.h"' > $tmp/next1/file1.h
+echo '#include_next "file2.h"' > $tmp/next2/file1.h
+echo 'foo' > $tmp/next3/file2.h
+$chibicc -I$tmp/next1 -I$tmp/next2 -I$tmp/next3 -E $tmp/file.c | grep -q foo
+check '#include_next'
+
 echo OK