checker, cgen: fix @[if xyz?] fn init() {}, add tests (#20096)

vlib/v/checker/fn.v

@@ -413,20 +413,23 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 	}
 	node.source_file = c.file
 
-	if node.name in c.table.fns && node.name != 'main.main' {
-		mut dep_names := []string{}
-		for stmt in node.stmts {
-			dnames := c.table.dependent_names_in_stmt(stmt)
-			for dname in dnames {
-				if dname in dep_names {
-					continue
+	if node.name in c.table.fns {
+		if node.name != 'main.main' {
+			mut dep_names := []string{}
+			for stmt in node.stmts {
+				dnames := c.table.dependent_names_in_stmt(stmt)
+				for dname in dnames {
+					if dname in dep_names {
+						continue
+					}
+					dep_names << dname
 				}
-				dep_names << dname
+			}
+			if dep_names.len > 0 {
+				c.table.fns[node.name].dep_names = dep_names
 			}
 		}
-		if dep_names.len > 0 {
-			c.table.fns[node.name].dep_names = dep_names
-		}
+		c.table.fns[node.name].source_fn = voidptr(node)
 	}
 
 	// vweb checks

vlib/v/gen/c/cgen.v

@@ -5869,14 +5869,14 @@ fn (mut g Gen) write_init_function() {
 			// ignore v.reflection already initialized above
 			continue
 		}
-		mut is_empty := true
+		mut const_section_header_shown := false
 		// write globals and consts init later
 		for var_name in g.sorted_global_const_names {
 			if var := g.global_const_defs[var_name] {
 				if var.mod == mod_name && var.init.len > 0 {
-					if is_empty {
-						is_empty = false
-						g.writeln('\t// Initializations for module ${mod_name}')
+					if !const_section_header_shown {
+						g.writeln('\t// Initializations of consts for module ${mod_name}')
+						const_section_header_shown = true
 					}
 					g.writeln(var.init)
 				}
@@ -5885,12 +5885,21 @@ fn (mut g Gen) write_init_function() {
 		init_fn_name := '${mod_name}.init'
 		if initfn := g.table.find_fn(init_fn_name) {
 			if initfn.return_type == ast.void_type && initfn.params.len == 0 {
-				if is_empty {
-					g.writeln('\t// Initializations for module ${mod_name}')
+				mut should_be_skipped := false
+				if initfn.source_fn != unsafe { nil } {
+					fndecl := unsafe { &ast.FnDecl(initfn.source_fn) }
+					if fndecl.should_be_skipped {
+						should_be_skipped = fndecl.should_be_skipped
+					}
+				}
+				if should_be_skipped {
+					g.writeln('\t// Skipping fn init() for module ${mod_name}')
+				} else {
+					g.writeln('\t// Calling fn init() for module ${mod_name}')
+					mod_c_name := util.no_dots(mod_name)
+					init_fn_c_name := '${mod_c_name}__init'
+					g.writeln('\t${init_fn_c_name}();')
 				}
-				mod_c_name := util.no_dots(mod_name)
-				init_fn_c_name := '${mod_c_name}__init'
-				g.writeln('\t${init_fn_c_name}();')
 			}
 		}
 		cleanup_fn_name := '${mod_name}.cleanup'

vlib/v/gen/c/testdata/init_fn_with_if_attr_defined.c.must_have

@@ -0,0 +1,2 @@
+// Calling fn init() for module main
+main__init();

vlib/v/gen/c/testdata/init_fn_with_if_attr_defined.out

@@ -0,0 +1,2 @@
+hi from init
+hi from main

vlib/v/gen/c/testdata/init_fn_with_if_attr_defined.vv

@@ -0,0 +1,10 @@
+// vtest vflags: -d init_on
+
+@[if init_on ?]
+fn init() {
+	println('hi from init')
+}
+
+fn main() {
+	println('hi from main')
+}

vlib/v/gen/c/testdata/init_fn_with_if_attr_not_defined.c.must_have

@@ -0,0 +1 @@
+// Skipping fn init() for module main

vlib/v/gen/c/testdata/init_fn_with_if_attr_not_defined.out

@@ -0,0 +1 @@
+hi from main

vlib/v/gen/c/testdata/init_fn_with_if_attr_not_defined.vv

@@ -0,0 +1,10 @@
+// vtest vflags: -d init_is_not_defined
+
+@[if init_on ?]
+fn init() {
+	println('hi from init')
+}
+
+fn main() {
+	println('hi from main')
+}