fmt: keep empty curlies and parenthesis as they are (#7329)

doc/docs.md

@@ -1509,8 +1509,7 @@ fn main() {
 ## References
 
 ```v
-struct Foo {
-}
+struct Foo {}
 
 fn (foo Foo) bar_method() {
 	// ...
@@ -1730,8 +1729,7 @@ struct Dog {
 	breed string
 }
 
-struct Cat {
-}
+struct Cat {}
 
 fn (d Dog) speak() string {
 	return 'woof'
@@ -1800,14 +1798,11 @@ A sum type instance can hold a value of several different types. Use the `type`
 keyword to declare a sum type:
 
 ```v
-struct Moon {
-}
+struct Moon {}
 
-struct Mars {
-}
+struct Mars {}
 
-struct Venus {
-}
+struct Venus {}
 
 type World = Mars | Moon | Venus
 
@@ -1824,14 +1819,11 @@ To check whether a sum type instance holds a certain type, use `sum is Type`.
 To cast a sum type to one of its variants you can use `sum as Type`:
 
 ```v
-struct Moon {
-}
+struct Moon {}
 
-struct Mars {
-}
+struct Mars {}
 
-struct Venus {
-}
+struct Venus {}
 
 type World = Mars | Moon | Venus
 
@@ -1883,14 +1875,11 @@ complex expression than just a variable name.
 You can also use `match` to determine the variant:
 
 ```v
-struct Moon {
-}
+struct Moon {}
 
-struct Mars {
-}
+struct Mars {}
 
-struct Venus {
-}
+struct Venus {}
 
 type World = Mars | Moon | Venus
 

vlib/v/fmt/fmt.v

@@ -297,8 +297,11 @@ pub fn (mut f Fmt) stmt(node ast.Stmt) {
 			if node.is_unsafe {
 				f.write('unsafe ')
 			}
-			f.writeln('{')
-			f.stmts(node.stmts)
+			f.write('{')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.writeln('}')
 		}
 		ast.BranchStmt {
@@ -306,36 +309,26 @@ pub fn (mut f Fmt) stmt(node ast.Stmt) {
 		}
 		ast.CompFor {
 			typ := f.no_cur_mod(f.table.type_to_str(node.typ))
-			f.writeln('\$for $node.val_var in ${typ}.$node.kind.str() {')
-			f.stmts(node.stmts)
+			f.write('\$for $node.val_var in ${typ}.$node.kind.str() {')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.writeln('}')
 		}
 		ast.ConstDecl {
 			f.const_decl(node)
 		}
 		ast.DeferStmt {
-			f.writeln('defer {')
-			f.stmts(node.stmts)
+			f.write('defer {')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.writeln('}')
 		}
 		ast.EnumDecl {
-			f.attrs(node.attrs)
-			if node.is_pub {
-				f.write('pub ')
-			}
-			name := node.name.after('.')
-			f.writeln('enum $name {')
-			f.comments(node.comments, inline: true, level: .indent)
-			for field in node.fields {
-				f.write('\t$field.name')
-				if field.has_expr {
-					f.write(' = ')
-					f.expr(field.expr)
-				}
-				f.comments(field.comments, inline: true, has_nl: false, level: .indent)
-				f.writeln('')
-			}
-			f.writeln('}\n')
+			f.enum_decl(node)
 		}
 		ast.ExprStmt {
 			f.comments(node.comments, {})
@@ -362,8 +355,11 @@ pub fn (mut f Fmt) stmt(node ast.Stmt) {
 			f.write('; ')
 			f.stmt(node.inc)
 			f.remove_new_line()
-			f.writeln(' {')
-			f.stmts(node.stmts)
+			f.write(' {')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.writeln('}')
 		}
 		ast.ForInStmt {
@@ -389,8 +385,11 @@ pub fn (mut f Fmt) stmt(node ast.Stmt) {
 				f.write(' .. ')
 				f.expr(node.high)
 			}
-			f.writeln(' {')
-			f.stmts(node.stmts)
+			f.write(' {')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.writeln('}')
 		}
 		ast.ForStmt {
@@ -400,11 +399,14 @@ pub fn (mut f Fmt) stmt(node ast.Stmt) {
 			f.write('for ')
 			f.expr(node.cond)
 			if node.is_inf {
-				f.writeln('{')
+				f.write('{')
 			} else {
-				f.writeln(' {')
+				f.write(' {')
+			}
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
 			}
-			f.stmts(node.stmts)
 			f.writeln('}')
 		}
 		ast.GlobalDecl {
@@ -597,6 +599,10 @@ pub fn (mut f Fmt) struct_decl(node ast.StructDecl) {
 		f.write(gtypes)
 		f.write('>')
 	}
+	if node.fields.len == 0 && node.pos.line_nr == node.pos.last_line {
+		f.writeln(' {}\n')
+		return
+	}
 	f.writeln(' {')
 	mut max := 0
 	mut max_type := 0
@@ -701,7 +707,10 @@ pub fn (mut f Fmt) interface_decl(node ast.InterfaceDecl) {
 		f.write('pub ')
 	}
 	name := node.name.after('.')
-	f.writeln('interface $name {')
+	f.write('interface $name {')
+	if node.methods.len > 0 || node.pos.line_nr < node.pos.last_line {
+		f.writeln('')
+	}
 	f.comments_after_last_field(node.pre_comments)
 	for method in node.methods {
 		f.write('\t')
@@ -712,6 +721,30 @@ pub fn (mut f Fmt) interface_decl(node ast.InterfaceDecl) {
 	f.writeln('}\n')
 }
 
+pub fn (mut f Fmt) enum_decl(node ast.EnumDecl) {
+	f.attrs(node.attrs)
+	if node.is_pub {
+		f.write('pub ')
+	}
+	name := node.name.after('.')
+	if node.fields.len == 0 && node.pos.line_nr == node.pos.last_line {
+		f.writeln('enum $name {}\n')
+		return
+	}
+	f.writeln('enum $name {')
+	f.comments(node.comments, inline: true, level: .indent)
+	for field in node.fields {
+		f.write('\t$field.name')
+		if field.has_expr {
+			f.write(' = ')
+			f.expr(field.expr)
+		}
+		f.comments(field.comments, inline: true, has_nl: false, level: .indent)
+		f.writeln('')
+	}
+	f.writeln('}\n')
+}
+
 pub fn (mut f Fmt) prefix_expr_cast_expr(fexpr ast.Expr) {
 	mut is_pe_amp_ce := false
 	mut ce := ast.CastExpr{}
@@ -1254,8 +1287,11 @@ pub fn (mut f Fmt) fn_decl(node ast.FnDecl) {
 	f.write(node.stringify(f.table, f.cur_mod, f.mod2alias)) // `Expr` instead of `ast.Expr` in mod ast
 	if node.language == .v {
 		if !node.no_body {
-			f.writeln(' {')
-			f.stmts(node.stmts)
+			f.write(' {')
+			if node.stmts.len > 0 || node.pos.line_nr < node.pos.last_line {
+				f.writeln('')
+				f.stmts(node.stmts)
+			}
 			f.write('}')
 		}
 		if !node.is_anon {
@@ -1908,6 +1944,10 @@ pub fn (mut f Fmt) const_decl(it ast.ConstDecl) {
 	if it.is_pub {
 		f.write('pub ')
 	}
+	if it.fields.len == 0 && it.pos.line_nr == it.pos.last_line {
+		f.writeln('const ()\n')
+		return
+	}
 	f.writeln('const (')
 	mut max := 0
 	for field in it.fields {

vlib/v/fmt/tests/empty_curlies_and_parens_keep.vv

@@ -0,0 +1,44 @@
+const ()
+
+const (
+)
+
+struct Bar {}
+
+struct Bar2 {
+}
+
+interface Spam {}
+
+interface Spam2 {
+}
+
+enum Baz {}
+
+enum Baz2 {
+}
+
+fn foo() {}
+
+fn foo2() {
+}
+
+fn main() {
+	arr := []int{}
+	x := 1
+	for s in arr {}
+	for s in arr {
+	}
+	for i := 0; i < 5; i++ {}
+	for j := 0; j < 5; j++ {
+	}
+	for false {}
+	for false {
+	}
+	defer {}
+	defer {
+	}
+	unsafe {}
+	unsafe {
+	}
+}

vlib/v/fmt/tests/struct_embed_expected.vv

@@ -2,8 +2,7 @@ struct Foo {
 	x int
 }
 
-struct Test {
-}
+struct Test {}
 
 struct Bar {
 	Foo

vlib/v/parser/parser.v

@@ -1827,7 +1827,7 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 	p.top_level_statement_end()
 	p.check(.rpar)
 	return ast.ConstDecl{
-		pos: start_pos.extend(end_pos)
+		pos: start_pos.extend_with_last_line(end_pos, p.prev_tok.line_nr)
 		fields: fields
 		is_pub: is_pub
 		end_comments: comments

vlib/v/parser/struct.v

@@ -459,7 +459,7 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 	}
 	p.top_level_statement_end()
 	p.check(.rcbr)
-	start_pos.last_line = p.prev_tok.line_nr
+	start_pos.last_line = p.prev_tok.line_nr - 1
 	return ast.InterfaceDecl{
 		name: interface_name
 		methods: methods