stage2: move C pointer allowzero error to AstGen

Author: Vexu

src/AstGen.zig

@@ -3104,6 +3104,10 @@ fn ptrType(
     node: Ast.Node.Index,
     ptr_info: Ast.full.PtrType,
 ) InnerError!Zir.Inst.Ref {
+    if (ptr_info.size == .C and ptr_info.allowzero_token != null) {
+        return gz.astgen.failTok(ptr_info.allowzero_token.?, "C pointers always allow address zero", .{});
+    }
+
     const elem_type = try typeExpr(gz, scope, ptr_info.ast.child_type);
 
     const simple = ptr_info.ast.align_node == 0 and

src/Sema.zig

@@ -13713,7 +13713,7 @@ fn zirPtrTypeSimple(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileErr
         .@"volatile" = inst_data.is_volatile,
         .size = inst_data.size,
     });
-    try sema.validatePtrTy(block, elem_ty_src, ty, inst_data.is_allowzero);
+    try sema.validatePtrTy(block, elem_ty_src, ty);
     return sema.addType(ty);
 }
 
@@ -13799,11 +13799,11 @@ fn zirPtrType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
         .@"volatile" = inst_data.flags.is_volatile,
         .size = inst_data.size,
     });
-    try sema.validatePtrTy(block, elem_ty_src, ty, inst_data.flags.is_allowzero);
+    try sema.validatePtrTy(block, elem_ty_src, ty);
     return sema.addType(ty);
 }
 
-fn validatePtrTy(sema: *Sema, block: *Block, elem_src: LazySrcLoc, ty: Type, explicit_allowzer: bool) CompileError!void {
+fn validatePtrTy(sema: *Sema, block: *Block, elem_src: LazySrcLoc, ty: Type) CompileError!void {
     const ptr_info = ty.ptrInfo().data;
     const pointee_tag = ptr_info.pointee_type.zigTypeTag();
     if (pointee_tag == .NoReturn) {
@@ -13814,8 +13814,6 @@ fn validatePtrTy(sema: *Sema, block: *Block, elem_src: LazySrcLoc, ty: Type, exp
         // TODO check extern type
         if (pointee_tag == .Opaque) {
             return sema.fail(block, elem_src, "C pointers cannot point to opaque types", .{});
-        } else if (explicit_allowzer) {
-            return sema.fail(block, elem_src, "C pointers always allow address zero", .{});
         }
     }
 }