checker: fix global empty const type check (fix #26324) (#26332)

Author: kbkpbot

vlib/v/checker/checker.v

@@ -66,6 +66,7 @@ pub mut:
 	expected_or_type            ast.Type // fn() or { 'this type' } eg. string. expected or block type
 	expected_expr_type          ast.Type // if/match is_expr: expected_type
 	mod                         string   // current module name
+	has_globals_in_module       bool     // true if the current module has @[has_globals] attribute
 	const_var                   &ast.ConstField = unsafe { nil } // the current constant, when checking const declarations
 	const_deps                  []string
 	const_names                 []string
@@ -218,6 +219,7 @@ fn (mut c Checker) reset_checker_state_at_start_of_new_file() {
 	c.inside_interface_deref = false
 	c.inside_decl_rhs = false
 	c.inside_if_guard = false
+	c.has_globals_in_module = false
 	c.error_details.clear()
 }
 
@@ -379,6 +381,14 @@ pub fn (mut c Checker) change_current_file(file &ast.File) {
 			import_sym.alias
 		}
 	}
+	// Check if the current module has has_globals attribute
+	c.has_globals_in_module = false
+	for attr in file.mod.attrs {
+		if attr.name == 'has_globals' {
+			c.has_globals_in_module = true
+			break
+		}
+	}
 }
 
 pub fn (mut c Checker) check_files(ast_files []&ast.File) {
@@ -2717,6 +2727,13 @@ fn (mut c Checker) branch_stmt(node ast.BranchStmt) {
 }
 
 fn (mut c Checker) global_decl(mut node ast.GlobalDecl) {
+	if !c.pref.enable_globals && !c.pref.is_fmt && !c.pref.is_vet && !c.pref.translated
+		&& !c.pref.is_livemain && !c.pref.building_v && !c.is_builtin_mod
+		&& !c.has_globals_in_module && !c.file.is_translated {
+		c.error('use `v -enable-globals ...` to enable globals', node.pos)
+		return
+	}
+
 	required_args_attr := ['_linker_section']
 	for attr_name in required_args_attr {
 		if attr := node.attrs.find_first(attr_name) {

vlib/v/checker/tests/globals_error.out

@@ -1,5 +1,5 @@
 vlib/v/checker/tests/globals_error.vv:1:1: error: use `v -enable-globals ...` to enable globals
     1 | __global (
-      | ~~~~~~~~
+      | ~~~~~~~~~~
     2 |     rfcnt int
     3 | )

vlib/v/checker/tests/with_check_option/empty_global_const.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/with_check_option/empty_global_const.vv:5:1: error: use `v -enable-globals ...` to enable globals
+    3 | const buf_len = 256
+    4 | 
+    5 | __global not_used_in_code_but_helps_triggering = u64(-1)
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    6 | 
+    7 | struct Buffer {

vlib/v/checker/tests/with_check_option/empty_global_const.vv

@@ -0,0 +1,18 @@
+module main
+
+const buf_len = 256
+
+__global not_used_in_code_but_helps_triggering = u64(-1)
+
+struct Buffer {
+mut:
+	data [256]u8
+	pos  int
+}
+
+fn (mut buf Buffer) clear() {
+	buf.pos = 0
+	for i in 0 .. buf_len {
+		buf.data[i] = 0
+	}
+}

vlib/v/parser/parser.v

@@ -2757,12 +2757,8 @@ fn (mut p Parser) global_decl() ast.GlobalDecl {
 		}
 	}
 
-	if !p.has_globals && !p.pref.enable_globals && !p.pref.is_fmt && !p.pref.is_vet
-		&& !p.pref.translated && !p.is_translated && !p.pref.is_livemain && !p.pref.building_v
-		&& !p.builtin_mod {
-		p.error('use `v -enable-globals ...` to enable globals')
-		return ast.GlobalDecl{}
-	}
+	// Parser always parses __global declarations correctly
+	// Checker will report an error if globals are not enabled
 	start_pos := p.tok.pos()
 	p.check(.key_global)
 	if p.disallow_declarations_in_script_mode() {