Support struct tags

parse.c

@@ -26,16 +26,30 @@ struct VarScope {
   Obj *var;
 };
 
+// Scope for struct tags
+typedef struct TagScope TagScope;
+struct TagScope {
+  TagScope *next;
+  char *name;
+  Type *ty;
+};
+
 // Represents a block scope.
 typedef struct Scope Scope;
 struct Scope {
   Scope *next;
+
+  // C has two block scopes; one is for variables and the other is
+  // for struct tags.
   VarScope *vars;
+  TagScope *tags;
 };
 
 // All local variable instances created during parsing are
 // accumulated to this list.
 static Obj *locals;
+
+// Likewise, global variables are accumulated to this list.
 static Obj *globals;
 
 static Scope *scope = &(Scope){};
@@ -76,6 +90,14 @@ static Obj *find_var(Token *tok) {
   return NULL;
 }
 
+static Type *find_tag(Token *tok) {
+  for (Scope *sc = scope; sc; sc = sc->next)
+    for (TagScope *sc2 = sc->tags; sc2; sc2 = sc2->next)
+      if (equal(tok, sc2->name))
+        return sc2->ty;
+  return NULL;
+}
+
 static Node *new_node(NodeKind kind, Token *tok) {
   Node *node = calloc(1, sizeof(Node));
   node->kind = kind;
@@ -167,6 +189,14 @@ static int get_number(Token *tok) {
   return tok->val;
 }
 
+static void push_tag_scope(Token *tok, Type *ty) {
+  TagScope *sc = calloc(1, sizeof(TagScope));
+  sc->name = strndup(tok->loc, tok->len);
+  sc->ty = ty;
+  sc->next = scope->tags;
+  scope->tags = sc;
+}
+
 // declspec = "char" | "int" | struct-decl
 static Type *declspec(Token **rest, Token *tok) {
   if (equal(tok, "char")) {
@@ -583,14 +613,27 @@ static void struct_members(Token **rest, Token *tok, Type *ty) {
   ty->members = head.next;
 }
 
-// struct-decl = "{" struct-members
+// struct-decl = ident? "{" struct-members
 static Type *struct_decl(Token **rest, Token *tok) {
-  tok = skip(tok, "{");
+  // Read a struct tag.
+  Token *tag = NULL;
+  if (tok->kind == TK_IDENT) {
+    tag = tok;
+    tok = tok->next;
+  }
+
+  if (tag && !equal(tok, "{")) {
+    Type *ty = find_tag(tag);
+    if (!ty)
+      error_tok(tag, "unknown struct type");
+    *rest = tok;
+    return ty;
+  }
 
   // Construct a struct object.
   Type *ty = calloc(1, sizeof(Type));
   ty->kind = TY_STRUCT;
-  struct_members(rest, tok, ty);
+  struct_members(rest, tok->next, ty);
   ty->align = 1;
 
   // Assign offsets within the struct to members.
@@ -605,6 +648,9 @@ static Type *struct_decl(Token **rest, Token *tok) {
   }
   ty->size = align_to(offset, ty->align);
 
+  // Register the struct type if a name was given.
+  if (tag)
+    push_tag_scope(tag, ty);
   return ty;
 }
 

test/struct.c

@@ -28,6 +28,11 @@ int main() {
   ASSERT(16, ({ struct {char a; int b;} x; sizeof(x); }));
   ASSERT(16, ({ struct {int a; char b;} x; sizeof(x); }));
 
+  ASSERT(16, ({ struct t {int a; int b;} x; struct t y; sizeof(y); }));
+  ASSERT(16, ({ struct t {int a; int b;}; struct t y; sizeof(y); }));
+  ASSERT(2, ({ struct t {char a[2];}; { struct t {char a[4];}; } struct t y; sizeof(y); }));
+  ASSERT(3, ({ struct t {int x;}; int t=1; struct t y; y.x=2; t+y.x; }));
+
   printf("OK\n");
   return 0;
 }