Add extern

Makefile

@@ -9,7 +9,8 @@ $(OBJS): chibi.h
 
 test: chibicc
 	./chibicc tests > tmp.s
-	echo 'int char_fn() { return 257; } int static_fn() { return 5; }' | \
+	echo 'int ext1; int *ext2; int char_fn() { return 257; }' \
+          'int static_fn() { return 5; }' | \
           gcc -xc -c -o tmp2.o -
 	gcc -static -o tmp tmp.s tmp2.o
 	./tmp

parse.c

@@ -168,6 +168,7 @@ static char *new_label(void) {
 typedef enum {
   TYPEDEF = 1 << 0,
   STATIC  = 1 << 1,
+  EXTERN  = 1 << 2,
 } StorageClass;
 
 static Function *function(void);
@@ -277,7 +278,7 @@ static Type *basetype(StorageClass *sclass) {
     Token *tok = token;
 
     // Handle storage class specifiers.
-    if (peek("typedef") || peek("static")) {
+    if (peek("typedef") || peek("static") || peek("extern")) {
       if (!sclass)
         error_tok(tok, "storage class specifier is not allowed");
 
@@ -285,9 +286,11 @@ static Type *basetype(StorageClass *sclass) {
         *sclass |= TYPEDEF;
       else if (consume("static"))
         *sclass |= STATIC;
+      else if (consume("extern"))
+        *sclass |= EXTERN;
 
       if (*sclass & (*sclass - 1))
-        error_tok(tok, "typedef and static may not be used together");
+        error_tok(tok, "typedef, static and extern may not be used together");
       continue;
     }
 
@@ -850,16 +853,21 @@ static void global_var(void) {
     return;
   }
 
-  Var *var = new_gvar(name, ty, true);
+  Var *var = new_gvar(name, ty, sclass != EXTERN);
 
-  if (!consume("=")) {
+  if (sclass == EXTERN) {
-    if (ty->is_incomplete)
-      error_tok(tok, "incomplete type");
     expect(";");
     return;
   }
 
-  var->initializer = gvar_initializer(ty);
+  if (consume("=")) {
+    var->initializer = gvar_initializer(ty);
+    expect(";");
+    return;
+  }
+
+  if (ty->is_incomplete)
+    error_tok(tok, "incomplete type");
   expect(";");
 }
 
@@ -1082,7 +1090,8 @@ static Node *read_expr_stmt(void) {
 static bool is_typename(void) {
   return peek("void") || peek("_Bool") || peek("char") || peek("short") ||
          peek("int") || peek("long") || peek("enum") || peek("struct") ||
-         peek("typedef") || peek("static") || find_typedef(token);
+         peek("typedef") || peek("static") || peek("extern") ||
+         find_typedef(token);
 }
 
 static Node *stmt(void) {

tests

@@ -42,6 +42,9 @@ int *g25=&g24;
 int g26[3] = {1, 2, 3};
 int *g27 = g26 + 1;
 
+extern int ext1;
+extern int *ext2;
+
 int assert(long expected, long actual, char *code) {
   if (expected == actual) {
     printf("%s => %ld\n", code, actual);
@@ -617,6 +620,12 @@ int main() {
   assert(3, *g25, "*g25");
   assert(2, *g27, "*g27");
 
+  ext1 = 5;
+  assert(5, ext1, "ext1");
+
+  ext2 = &ext1;
+  assert(5, *ext2, "*ext2");
+
   printf("OK\n");
   return 0;
 }

tokenize.c

@@ -150,7 +150,8 @@ static char *starts_with_reserved(char *p) {
   static char *kw[] = {"return", "if", "else", "while", "for", "int",
                        "char", "sizeof", "struct", "typedef", "short",
                        "long", "void", "_Bool", "enum", "static", "break",
-                       "continue", "goto", "switch", "case", "default"};
+                       "continue", "goto", "switch", "case", "default",
+                       "extern"};
 
   for (int i = 0; i < sizeof(kw) / sizeof(*kw); i++) {
     int len = strlen(kw[i]);