parser: struct updating syntax with `Abc{...oldabc newfield: val}` (#7865)

vlib/v/ast/ast.v

@@ -247,13 +247,16 @@ pub mut:
 
 pub struct StructInit {
 pub:
-	pos          token.Position
+	pos              token.Position
-	is_short     bool
+	is_short         bool
 pub mut:
-	pre_comments []Comment
+	pre_comments     []Comment
-	typ          table.Type
+	typ              table.Type
-	fields       []StructInitField
+	update_expr      Expr
-	embeds       []StructInitEmbed
+	update_expr_type table.Type
+	has_update_expr  bool
+	fields           []StructInitField
+	embeds           []StructInitEmbed
 }
 
 // import statement

vlib/v/checker/checker.v

@@ -641,6 +641,17 @@ pub fn (mut c Checker) struct_init(mut struct_init ast.StructInit) table.Type {
 		}
 		else {}
 	}
+	if struct_init.has_update_expr {
+		update_type := c.expr(struct_init.update_expr)
+		struct_init.update_expr_type = update_type
+		update_sym := c.table.get_type_symbol(update_type)
+		sym := c.table.get_type_symbol(struct_init.typ)
+		if update_sym.kind != .struct_ {
+			c.error('expected struct `$sym.name`, found `$update_sym.name`', struct_init.update_expr.position())
+		} else if update_type != struct_init.typ {
+			c.error('expected struct `$sym.name`, found struct `$update_sym.name`', struct_init.update_expr.position())
+		}
+	}
 	return struct_init.typ
 }
 

vlib/v/checker/tests/struct_init_update_struct_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_init_update_struct_err.vv:11:6: error: expected struct `Foo`, found struct `Foo2`
+    9 |     f3 := Foo2{}
+   10 |     _ := Foo{
+   11 |         ...f3
+      |            ~~
+   12 |         name: 'f2'
+   13 |     }

vlib/v/checker/tests/struct_init_update_struct_err.vv

@@ -0,0 +1,15 @@
+struct Foo {
+	name string
+	age int
+}
+
+struct Foo2 {}
+
+fn main() {
+	f3 := Foo2{}
+	_ := Foo{
+		...f3
+		name: 'f2'
+	}
+}
+

vlib/v/checker/tests/struct_init_update_type_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_init_update_type_err.vv:11:6: error: expected struct `Foo`, found `int`
+    9 |     f3 := 2
+   10 |     _ := Foo{
+   11 |         ...f3
+      |            ~~
+   12 |         name: 'f2'
+   13 |     }

vlib/v/checker/tests/struct_init_update_type_err.vv

@@ -0,0 +1,15 @@
+struct Foo {
+	name string
+	age int
+}
+
+struct Foo2 {}
+
+fn main() {
+	f3 := 2
+	_ := Foo{
+		...f3
+		name: 'f2'
+	}
+}
+

vlib/v/fmt/fmt.v

@@ -2015,7 +2015,7 @@ pub fn (mut f Fmt) struct_init(it ast.StructInit) {
 	if name == 'void' {
 		name = ''
 	}
-	if it.fields.len == 0 {
+	if it.fields.len == 0 && !it.has_update_expr {
 		// `Foo{}` on one line if there are no fields or comments
 		if it.pre_comments.len == 0 {
 			f.write('$name{}')
@@ -2029,6 +2029,11 @@ pub fn (mut f Fmt) struct_init(it ast.StructInit) {
 		// if name != '' {
 		f.write('$name{')
 		// }
+		if it.has_update_expr {
+			f.write('...')
+			f.expr(it.update_expr)
+			f.write(', ')
+		}
 		for i, field in it.fields {
 			f.prefix_expr_cast_expr(field.expr)
 			if i < it.fields.len - 1 {
@@ -2049,6 +2054,11 @@ pub fn (mut f Fmt) struct_init(it ast.StructInit) {
 		}
 		init_start := f.out.len
 		f.indent++
+		if it.has_update_expr {
+			f.write('...')
+			f.expr(it.update_expr)
+			f.writeln('')
+		}
 		short_args_loop: for {
 			f.comments(it.pre_comments, inline: true, has_nl: true, level: .keep)
 			for i, field in it.fields {

vlib/v/fmt/tests/struct_update_keep.vv

@@ -0,0 +1,17 @@
+struct Foo {
+	name string
+	age  int
+}
+
+struct Foo2 {}
+
+fn main() {
+	f := Foo{
+		name: 'test'
+		age: 18
+	}
+	f2 := Foo{
+		...f
+		name: 'f2'
+	}
+}

vlib/v/gen/cgen.v

@@ -4529,7 +4529,17 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 			if field.typ in info.embeds {
 				continue
 			}
-			g.zero_struct_field(field)
+			if struct_init.has_update_expr {
+				g.expr(struct_init.update_expr)
+				if struct_init.update_expr_type.is_ptr() {
+					g.write('->')
+				} else {
+					g.write('.')
+				}
+				g.write(field.name)
+			} else {
+				g.zero_struct_field(field)
+			}
 			if is_multiline {
 				g.writeln(',')
 			} else {

vlib/v/parser/struct.v

@@ -331,21 +331,29 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 	pre_comments := p.eat_comments()
 	mut fields := []ast.StructInitField{}
 	mut i := 0
-	no_keys := p.peek_tok.kind != .colon && p.tok.kind != .rcbr // `Vec{a,b,c}
+	no_keys := p.peek_tok.kind != .colon && p.tok.kind != .rcbr && p.tok.kind != .ellipsis // `Vec{a,b,c}
 	// p.warn(is_short_syntax.str())
 	saved_is_amp := p.is_amp
 	p.is_amp = false
+	mut update_expr := ast.Expr{}
+	mut has_update_expr := false
 	for p.tok.kind !in [.rcbr, .rpar, .eof] {
 		mut field_name := ''
 		mut expr := ast.Expr{}
 		mut field_pos := token.Position{}
 		mut comments := []ast.Comment{}
 		mut nline_comments := []ast.Comment{}
+		is_update_expr := fields.len == 0 && p.tok.kind == .ellipsis
 		if no_keys {
 			// name will be set later in checker
 			expr = p.expr(0)
 			field_pos = expr.position()
 			comments = p.eat_line_end_comments()
+		} else if is_update_expr {
+			// struct updating syntax; f2 := Foo{ ...f, name: 'f2' }
+			p.check(.ellipsis)
+			update_expr = p.expr(0)
+			has_update_expr = true
 		} else {
 			first_field_pos := p.tok.position()
 			field_name = p.check_name()
@@ -367,12 +375,14 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 		}
 		comments << p.eat_line_end_comments()
 		nline_comments << p.eat_comments()
-		fields << ast.StructInitField{
+		if !is_update_expr {
-			name: field_name
+			fields << ast.StructInitField{
-			expr: expr
+				name: field_name
-			pos: field_pos
+				expr: expr
-			comments: comments
+				pos: field_pos
-			next_comments: nline_comments
+				comments: comments
+				next_comments: nline_comments
+			}
 		}
 	}
 	last_pos := p.tok.position()
@@ -383,6 +393,8 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 	node := ast.StructInit{
 		typ: typ
 		fields: fields
+		update_expr: update_expr
+		has_update_expr: has_update_expr
 		pos: token.Position{
 			line_nr: first_pos.line_nr
 			pos: first_pos.pos

vlib/v/parser/tests/struct_update_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/struct_update_err.vv:15:3: error: unexpected `...`, expecting `name`
+   13 |     f2 := Foo{
+   14 |         name: 'f2'
+   15 |         ...f
+      |         ~~~
+   16 |     }
+   17 | }

vlib/v/parser/tests/struct_update_err.vv

@@ -0,0 +1,17 @@
+struct Foo {
+	name string
+	age  int
+}
+
+struct Foo2 {}
+
+fn main() {
+	f := Foo{
+		name: 'test'
+		age: 18
+	}
+	f2 := Foo{
+		name: 'f2'
+		...f
+	}
+}

vlib/v/tests/struct_test.v

@@ -366,3 +366,15 @@ fn test_fields_array_of_fn() {
     println(commands.show)
 	assert '$commands.show' == '[fn () string, fn () string]'
 }
+
+fn test_struct_update() {
+	c := Country{name: 'test'}
+	c2 := Country{
+		...c
+		capital: City{
+			name: 'city'
+		}
+	}
+	assert c2.capital.name == 'city'
+	assert c2.name == 'test'
+}