vfmt: skip skipped modules; add module test

vlib/v/ast/ast.v

@@ -96,6 +96,7 @@ pub:
 	name string
 	path string
 	expr Expr
+	is_skipped bool // module main can be skipped in single file programs
 }
 
 pub struct StructField {

vlib/v/checker/checker.v

@@ -61,7 +61,7 @@ pub fn (c mut Checker) check_files(ast_files []ast.File) {
 		c.check(file)
 	}
 	// Make sure fn main is defined in non lib builds
-	if c.pref.build_mode == .build_module {
+	if c.pref.build_mode == .build_module || c.pref.is_test {
 		return
 	}
 	for i, f in c.table.fns {

vlib/v/fmt/fmt.v

@@ -74,8 +74,11 @@ pub fn (f mut Fmt) writeln(s string) {
 }
 
 fn (f mut Fmt) mod(mod ast.Module) {
-	f.writeln('module $mod.name\n')
 	f.cur_mod = mod.name
+	if mod.is_skipped {
+		return
+	}
+	f.writeln('module $mod.name\n')
 }
 
 fn (f mut Fmt) imports(imports []ast.Import) {

vlib/v/fmt/tests/module_struct_keep.vv

@@ -0,0 +1,10 @@
+module module_fmt
+
+pub struct MyStruct {
+mut:
+	value int
+}
+
+pub fn (m MyStruct) foo() bool {
+	return true
+}

vlib/v/parser/parser.v

@@ -254,10 +254,6 @@ fn (p mut Parser) check_name() string {
 }
 
 pub fn (p mut Parser) top_stmt() ast.Stmt {
-	if p.fileis('mmm.v') {
-		print('!!stmt()')
-		println(p.tok.kind.str())
-	}
 	match p.tok.kind {
 		.key_pub {
 			match p.peek_tok.kind {
@@ -518,7 +514,6 @@ fn (p mut Parser) range_expr(low ast.Expr) ast.Expr {
 	return node
 }
 */
-
 pub fn (p &Parser) error(s string) {
 	p.error_with_pos(s, p.tok.position())
 }
@@ -1409,7 +1404,8 @@ fn (p mut Parser) parse_number_literal() ast.Expr {
 
 fn (p mut Parser) module_decl() ast.Module {
 	mut name := 'main'
-	if p.tok.kind == .key_module {
+	is_skipped := p.tok.kind != .key_module
+	if !is_skipped {
 		p.check(.key_module)
 		name = p.check_name()
 	}
@@ -1418,6 +1414,7 @@ fn (p mut Parser) module_decl() ast.Module {
 	p.builtin_mod = p.mod == 'builtin'
 	return ast.Module{
 		name: full_mod
+		is_skipped: is_skipped
 	}
 }