parser: implement parsing of `select` block (#6379)

vlib/v/ast/ast.v

@@ -12,7 +12,7 @@ pub type TypeDecl = AliasTypeDecl | FnTypeDecl | SumTypeDecl
 pub type Expr = AnonFn | ArrayInit | AsCast | Assoc | BoolLiteral | CallExpr | CastExpr |
 	ChanInit | CharLiteral | Comment | ComptimeCall | ConcatExpr | EnumVal | FloatLiteral |
 	Ident | IfExpr | IfGuardExpr | IndexExpr | InfixExpr | IntegerLiteral | Likely | LockExpr |
-	MapInit | MatchExpr | None | OrExpr | ParExpr | PostfixExpr | PrefixExpr | RangeExpr |
+	MapInit | MatchExpr | None | OrExpr | ParExpr | PostfixExpr | PrefixExpr | RangeExpr | SelectExpr |
 	SelectorExpr | SizeOf | SqlExpr | StringInterLiteral | StringLiteral | StructInit | Type |
 	TypeOf | UnsafeExpr
 
@@ -536,6 +536,27 @@ pub:
 	post_comments []Comment
 }
 
+pub struct SelectExpr {
+pub:
+	branches      []SelectBranch
+	pos           token.Position
+pub mut:
+	is_expr       bool // returns a value
+	return_type   table.Type
+	expected_type table.Type // for debugging only
+}
+
+pub struct SelectBranch {
+pub:
+	stmt          Stmt // `a := <-ch` or `ch <- a`
+	stmts         []Stmt // right side
+	pos           token.Position
+	comment       Comment // comment above `select {`
+	is_else       bool
+	is_timeout    bool
+	post_comments []Comment
+}
+
 /*
 CompIf.is_opt:
 `$if xyz? {}` => this compile time `if` is optional,
@@ -1062,6 +1083,9 @@ pub fn (expr Expr) position() token.Position {
 			return expr.pos
 		}
 		// ast.ParExpr { }
+		SelectExpr {
+			return expr.pos
+		}
 		SelectorExpr {
 			return expr.pos
 		}

vlib/v/checker/checker.v

@@ -2641,6 +2641,10 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 			// never happens
 			return table.void_type
 		}
+		ast.SelectExpr {
+			// TODO: to be implemented
+			return table.void_type
+		}
 		ast.SelectorExpr {
 			return c.selector_expr(mut node)
 		}

vlib/v/fmt/fmt.v

@@ -953,6 +953,9 @@ pub fn (mut f Fmt) expr(node ast.Expr) {
 			f.write('..')
 			f.expr(node.high)
 		}
+		ast.SelectExpr {
+			// TODO: implement this
+		}
 		ast.SelectorExpr {
 			f.expr(node.expr)
 			f.write('.')

vlib/v/gen/cgen.v

@@ -2137,6 +2137,9 @@ fn (mut g Gen) expr(node ast.Expr) {
 		ast.RangeExpr {
 			// Only used in IndexExpr
 		}
+		ast.SelectExpr {
+			// TODO: to be implemented
+		}
 		ast.SizeOf {
 			if node.is_type {
 				node_typ := g.unwrap_generic(node.typ)

vlib/v/gen/js/js.v

@@ -619,6 +619,9 @@ fn (mut g JsGen) expr(node ast.Expr) {
 		ast.RangeExpr {
 			// Only used in IndexExpr, requires index type info
 		}
+		ast.SelectExpr {
+			// TODO: to be implemented
+		}
 		ast.SelectorExpr {
 			g.gen_selector_expr(node)
 		}

vlib/v/parser/if_match.v

@@ -288,3 +288,139 @@ fn (mut p Parser) match_expr() ast.MatchExpr {
 		var_name: var_name
 	}
 }
+
+fn (mut p Parser) select_expr() ast.SelectExpr {
+	match_first_pos := p.tok.position()
+	p.check(.key_select)
+	no_lcbr := p.tok.kind != .lcbr
+	if !no_lcbr {
+		p.check(.lcbr)
+	}
+	mut branches := []ast.SelectBranch{}
+	mut has_else := false
+	mut has_timeout := false
+	for {
+		branch_first_pos := p.tok.position()
+		comment := p.check_comment() // comment before {}
+		p.open_scope()
+		// final else
+		mut is_else := false
+		mut is_timeout := false
+		mut stmt := ast.Stmt{}
+		if p.tok.kind == .key_else {
+			if has_timeout {
+				p.error_with_pos('timeout `> t` and `else` are mutually exclusive `select` keys', p.tok.position())
+			}
+			if has_else {
+				p.error_with_pos('at most one `else` branch allowed in `select` block', p.tok.position())
+			}
+			is_else = true
+			has_else = true
+			p.next()
+		} else if p.tok.kind == .gt {
+			if has_else {
+				p.error_with_pos('`else` and timeout `> t` are mutually exclusive `select` keys', p.tok.position())
+			}
+			if has_timeout {
+				p.error_with_pos('at most one timeout `> t` branch allowed in `select` block', p.tok.position())
+			}
+			is_timeout = true
+			has_timeout = true
+			p.next()
+			p.inside_match = true
+			expr := p.expr(0)
+			p.inside_match = false
+			stmt = ast.ExprStmt{
+				expr: expr
+				pos: expr.position()
+				comments: [comment]
+				is_expr: true
+			}
+		} else {
+			p.inside_match = true
+			exprs, comments := p.expr_list()
+			if exprs.len != 1 {
+				p.error('only one expression allowed as `select` key')
+			}
+			if p.tok.kind in [.assign, .decl_assign] {
+				stmt = p.partial_assign_stmt(exprs, comments)
+			} else {
+				stmt = ast.ExprStmt{
+					expr: exprs[0]
+					pos: exprs[0].position()
+					comments: [comment]
+					is_expr: true
+				}
+			}
+			p.inside_match = false
+			match stmt {
+				ast.ExprStmt {
+					if !stmt.is_expr {
+						p.error_with_pos('select: invalid expression', stmt.pos)
+					} else {
+						match stmt.expr as expr {
+							ast.InfixExpr {
+								if expr.op != .arrow {
+									p.error_with_pos('select key: `<-` operator expected', expr.pos)
+								}
+							}
+							else {
+								p.error_with_pos('select key: send expression (`ch <- x`) expected', stmt.pos)
+							}
+						}
+					}
+				}
+				ast.AssignStmt {
+					match stmt.right[0] as expr {
+						ast.PrefixExpr {
+							if expr.op != .arrow {
+								p.error_with_pos('select key: `<-` operator expected', expr.pos)
+							}
+						} else {
+							p.error_with_pos('select key: receive expression expected', stmt.right[0].position())
+						}
+					}
+				}
+				else {
+					p.error_with_pos('select: transmission statement expected', stmt.position())
+				}
+			}
+		}
+		branch_last_pos := p.tok.position()
+		p.inside_match_body = true
+		stmts := p.parse_block_no_scope(false)
+		p.close_scope()
+		p.inside_match_body = false
+		pos := token.Position{
+			line_nr: branch_first_pos.line_nr
+			pos: branch_first_pos.pos
+			len: branch_last_pos.pos - branch_first_pos.pos + branch_last_pos.len
+		}
+		post_comments := p.eat_comments()
+		branches << ast.SelectBranch{
+			stmt: stmt
+			stmts: stmts
+			pos: pos
+			comment: comment
+			is_else: is_else
+			is_timeout: is_timeout
+			post_comments: post_comments
+		}
+		if p.tok.kind == .rcbr || ((is_else || is_timeout) && no_lcbr) {
+			break
+		}
+	}
+	match_last_pos := p.tok.position()
+	pos := token.Position{
+		line_nr: match_first_pos.line_nr
+		pos: match_first_pos.pos
+		len: match_last_pos.pos - match_first_pos.pos + match_last_pos.len
+	}
+	if p.tok.kind == .rcbr {
+		p.check(.rcbr)
+	}
+	return ast.SelectExpr{
+		branches: branches
+		pos: pos
+	}
+}

vlib/v/parser/parser.v

@@ -859,8 +859,9 @@ fn (mut p Parser) parse_multi_expr(is_top_level bool) ast.Stmt {
 	}
 	if p.tok.kind in [.assign, .decl_assign] || p.tok.kind.is_assign() {
 		return p.partial_assign_stmt(left, left_comments)
-	} else if is_top_level && tok.kind !in [.key_if, .key_match, .key_lock, .key_rlock] &&
-		left0 !is ast.CallExpr && left0 !is ast.PostfixExpr && !(left0 is ast.InfixExpr &&
+	} else if is_top_level && tok.kind !in
+		[.key_if, .key_match, .key_lock, .key_rlock, .key_select] && left0 !is ast.CallExpr &&
+		left0 !is ast.PostfixExpr && !(left0 is ast.InfixExpr &&
 		(left0 as ast.InfixExpr).op in [.left_shift, .arrow]) && left0 !is ast.ComptimeCall {
 		p.error_with_pos('expression evaluated but not used', left0.position())
 	}

vlib/v/parser/pratt.v

@@ -74,6 +74,9 @@ pub fn (mut p Parser) expr(precedence int) ast.Expr {
 		.key_match {
 			node = p.match_expr()
 		}
+		.key_select {
+			node = p.select_expr()
+		}
 		.number {
 			node = p.parse_number_literal()
 		}

vlib/v/parser/tests/select_bad_key_1.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_bad_key_1.vv:39:8: error: select key: receive expression expected
+   37 | fn f3_bad(ch1 chan St) {
+   38 |     select {
+   39 |         b := 17 {
+      |              ~~
+   40 |             println(b)
+   41 |         }

vlib/v/parser/tests/select_bad_key_1.vv

@@ -0,0 +1,47 @@
+import time
+
+struct St {
+	a int
+}
+
+fn f1_good(ch1 chan St, ch2 chan int, ch3 chan int) {
+	mut a := 5
+	select {
+		a = <- ch3 {
+			println(a)
+		}
+		b := <- ch1 {
+			println(b.a)
+		}
+		ch1 <- a {
+			a++
+		}
+		> 50 * time.millisecond {
+			println('timeout')
+		}
+	}
+	println('done')
+}
+
+fn f2_good(ch1 chan St) {
+	select {
+		b := <- ch1 {
+			println(b)
+		}
+		else {
+			println('no channel ready')
+		}
+	}
+}
+
+fn f3_bad(ch1 chan St) {
+	select {
+		b := 17 {
+			println(b)
+		}
+	}
+}
+
+fn main() {}
+
+			

vlib/v/parser/tests/select_bad_key_2.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_bad_key_2.vv:7:5: error: select key: `<-` operator expected
+    5 |             println(b)
+    6 |         }
+    7 |         a + 7 {
+      |           ^
+    8 |             println("shouldn't get here")
+    9 |         }

vlib/v/parser/tests/select_bad_key_2.vv

@@ -0,0 +1,13 @@
+fn f3_bad(ch1 chan int) {
+	a := 5
+	select {
+		b := <-ch1 {
+			println(b)
+		}
+		a + 7 {
+			println("shouldn't get here")
+		}
+	}
+}
+
+fn main() {}

vlib/v/parser/tests/select_bad_key_3.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_bad_key_3.vv:7:3: error: select key: send expression (`ch <- x`) expected
+    5 |             println(b)
+    6 |         }
+    7 |         println(7) {
+      |         ~~~~~~~~~~
+    8 |             println("shouldn't get here")
+    9 |         }

vlib/v/parser/tests/select_bad_key_3.vv

@@ -0,0 +1,13 @@
+fn f3_bad(ch1 chan int) {
+	a := 5
+	select {
+		b := <-ch1 {
+			println(b)
+		}
+		println(7) {
+			println("shouldn't get here")
+		}
+	}
+}
+
+fn main() {}

vlib/v/parser/tests/select_bad_key_4.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_bad_key_4.vv:7:8: error: select key: `<-` operator expected
+    5 |             println(b)
+    6 |         }
+    7 |         c := -a {
+      |              ^
+    8 |             println("shouldn't get here")
+    9 |         }

vlib/v/parser/tests/select_bad_key_4.vv

@@ -0,0 +1,13 @@
+fn f3_bad(ch1 chan int) {
+	mut a := 5
+	select {
+		a = <-ch1 {
+			println(b)
+		}
+		c := -a {
+			println("shouldn't get here")
+		}
+	}
+}
+
+fn main() {}

vlib/v/parser/tests/select_else_1.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_else_1.vv:12:3: error: `else` and timeout `> t` are mutually exclusive `select` keys
+   10 |             println("shouldn't get here")
+   11 |         }
+   12 |         > 30 * time.millisecond {
+      |         ^
+   13 |             println('bad')
+   14 |         }

vlib/v/parser/tests/select_else_1.vv

@@ -0,0 +1,18 @@
+import time
+
+fn f3_bad(ch1 chan int) {
+	a := 5
+	select {
+		b := <-ch1 {
+			println(b)
+		}
+		else {
+			println("shouldn't get here")
+		}
+		> 30 * time.millisecond {
+			println('bad')
+		}
+	}
+}
+
+fn main() {}

vlib/v/parser/tests/select_else_2.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/select_else_2.vv:12:3: error: timeout `> t` and `else` are mutually exclusive `select` keys
+   10 |             println('bad')
+   11 |         }
+   12 |         else {
+      |         ~~~~
+   13 |             println("shouldn't get here")
+   14 |         }

vlib/v/parser/tests/select_else_2.vv

@@ -0,0 +1,18 @@
+import time
+
+fn f3_bad(ch1 chan int) {
+	a := 5
+	select {
+		b := <-ch1 {
+			println(b)
+		}
+		> 30 * time.millisecond {
+			println('bad')
+		}
+		else {
+			println("shouldn't get here")
+		}
+	}
+}
+
+fn main() {}