From 4ae88c69ac12a9e0e49602d9abfc8095a7a00f73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kr=C3=BCger?=
 <45282134+UweKrueger@users.noreply.github.com>
Date: Sun, 20 Sep 2020 03:50:09 +0200
Subject: [PATCH] sync/select: allow push of literals and calculated
 expressions (#6429)

---
 vlib/sync/channel_select_2_test.v | 19 ++++----------
 vlib/sync/channel_select_3_test.v | 24 ++++++++++++++----
 vlib/sync/channel_select_test.v   |  8 ++++++
 vlib/v/checker/checker.v          | 42 +++++++++++++++++++++++++++++++
 vlib/v/gen/cgen.v                 | 20 ++++++++++++---
 vlib/v/parser/if_match.v          |  2 ++
 vlib/v/parser/parser.v            |  5 +++-
 7 files changed, 96 insertions(+), 24 deletions(-)

diff --git a/vlib/sync/channel_select_2_test.v b/vlib/sync/channel_select_2_test.v
index 1a4f3a216a..055b49abbc 100644
--- a/vlib/sync/channel_select_2_test.v
+++ b/vlib/sync/channel_select_2_test.v
@@ -36,32 +36,23 @@ fn test_select() {
 	go do_send_int(chi)
 	go do_send_byte(chb)
 	go do_send_i64(chl)
-	mut channels := [&sync.Channel(chi), &sync.Channel(recch), &sync.Channel(chl), &sync.Channel(chb)]
-	directions := [sync.Direction.pop, .push, .pop, .pop]
 	mut sum := i64(0)
 	mut rl := i64(0)
-	mut ri := int(0)
-	mut rb := byte(0)
 	mut sl := i64(0)
-	mut objs := [voidptr(&ri), &sl, &rl, &rb]
 	for _ in 0 .. 1200 {
-		idx := sync.channel_select(mut channels, directions, mut objs, -1)
-		match idx {
-			0 {
+		select {
+			ri := <-chi {
 				sum += ri
 			}
-			1 {
+			recch <- sl {
 				sl++
 			}
-			2 {
+			rl = <-chl {
 				sum += rl
 			}
-			3 {
+			rb := <-chb {
 				sum += rb
 			}
-			else {
-				println('got $idx (timeout)')
-			}
 		}
 	}
 	// Use Gauß' formula for the first 2 contributions
diff --git a/vlib/sync/channel_select_3_test.v b/vlib/sync/channel_select_3_test.v
index b679cb9fd7..70bc0b2857 100644
--- a/vlib/sync/channel_select_3_test.v
+++ b/vlib/sync/channel_select_3_test.v
@@ -5,9 +5,12 @@ struct St {
 	a int
 }
 
-fn f1(ch1 chan int, ch2 chan St, ch3 chan int, sem sync.Semaphore) {
+fn getint() int {
+	return 8
+}
+
+fn f1(ch1 chan int, ch2 chan St, ch3 chan int, ch4 chan int, ch5 chan int, sem sync.Semaphore) {
 	mut a := 5
-	st := St{}
 	select {
 		a = <-ch3 {
 			a = 0
@@ -15,9 +18,18 @@ fn f1(ch1 chan int, ch2 chan St, ch3 chan int, sem sync.Semaphore) {
 		b := <-ch2 {
 			a = b.a
 		}
-		ch2 <- st {
+		ch3 <- 5 {
+			a = 1
+		}
+		ch2 <- St{a: 37} {
 			a = 2
 		}
+		ch4 <- (6 + 7 * 9) {
+			a = 8
+		}
+		ch5 <- getint() {
+			a = 9
+		}
 		> 300 * time.millisecond {
 			a = 3
 		}
@@ -30,7 +42,7 @@ fn f2(ch1 chan St, ch2 chan int, sem sync.Semaphore) {
 	mut r := 23
 	for i in 0 .. 2 {
 		select {
-			b := <- ch1 {
+			b := <-ch1 {
 				r = b.a
 			}
 			ch2 <- r {
@@ -50,6 +62,8 @@ fn test_select_blocks() {
 	ch1 := chan int{cap: 1}
 	ch2 := chan St{}
 	ch3 := chan int{}
+	ch4 := chan int{}
+	ch5 := chan int{}
 	sem := sync.new_semaphore()
 	mut r := false
 	t := select {
@@ -69,7 +83,7 @@ fn test_select_blocks() {
 	ch2 <- St{a: 13}
 	sem.wait()
 	stopwatch := time.new_stopwatch({})
-	go f1(ch1, ch2, ch3, sem)
+	go f1(ch1, ch2, ch3, ch4, ch5, sem)
 	sem.wait()
 	elapsed_ms := f64(stopwatch.elapsed()) / time.millisecond
 	assert elapsed_ms >= 295.0
diff --git a/vlib/sync/channel_select_test.v b/vlib/sync/channel_select_test.v
index 3131bc5658..2d99cd2a05 100644
--- a/vlib/sync/channel_select_test.v
+++ b/vlib/sync/channel_select_test.v
@@ -1,3 +1,11 @@
+/*
+ * ATTENTION! Do not use this file as an example!
+ * For that, please look at `channel_select_2_test.v` or `channel_select_3_test.v`
+ *
+ * This test case uses the implementation in `sync/channels.v` directly
+ * in order to test it independently from the support in the core language
+ */
+
 import sync
 
 fn do_rec_i64(mut ch sync.Channel) {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 40860e0bbf..906d34592e 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3064,6 +3064,48 @@ pub fn (mut c Checker) select_expr(mut node ast.SelectExpr) table.Type {
 	node.expected_type = c.expected_type
 	for branch in node.branches {
 		c.stmt(branch.stmt)
+		match branch.stmt as stmt {
+			ast.ExprStmt {
+				if branch.is_timeout {
+					if !stmt.typ.is_int() {
+						tsym := c.table.get_type_symbol(stmt.typ)
+						c.error('invalid type `$tsym.name` for timeout - expected integer type aka `time.Duration`',
+							stmt.pos)
+					}
+				} else {
+					if stmt.expr is ast.InfixExpr as expr {
+						if expr.left !is ast.Ident &&
+							expr.left !is ast.SelectorExpr && expr.left !is ast.IndexExpr {
+							c.error('channel in `select` key must be predefined', expr.left.position())
+						}
+					} else {
+						c.error('invalid expression for `select` key', stmt.expr.position())
+					}
+				}
+			}
+			ast.AssignStmt {
+				match stmt.right[0] as expr {
+					ast.PrefixExpr {
+						if expr.right !is ast.Ident &&
+							expr.right !is ast.SelectorExpr && expr.right !is ast.IndexExpr {
+							c.error('channel in `select` key must be predefined', expr.right.position())
+						}
+						if expr.or_block.kind != .absent {
+							err_prefix := if expr.or_block.kind == .block { 'or block' } else { 'error propagation' }
+							c.error('$err_prefix not allowed in `select` key', expr.or_block.pos)
+						}
+					}
+					else {
+						c.error('`<-` receive expression expected', stmt.right[0].position())
+					}
+				}
+			}
+			else {
+				if !branch.is_else {
+					c.error('receive or send statement expected as `select` key', branch.stmt.position())
+				}
+			}
+		}
 		c.stmts(branch.stmts)
 	}
 	return table.bool_type
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index e9160a965e..7a63cb6ce6 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -2767,11 +2767,23 @@ fn (mut g Gen) select_expr(node ast.SelectExpr) {
 		} else {
 			match branch.stmt as stmt {
 				ast.ExprStmt {
+					// send expression
 					expr := stmt.expr as ast.InfixExpr
 					channels << expr.left
-					objs << expr.right
-					tmp_objs << ''
-					elem_types << ''
+					if expr.right is ast.Ident ||
+						expr.right is ast.IndexExpr || expr.right is ast.SelectorExpr || expr.right is ast.StructInit {
+						// addressable objects in the `C` output
+						objs << expr.right
+						tmp_objs << ''
+						elem_types << ''
+					} else {
+						// must be evaluated to tmp var before real `select` is performed
+						objs << ast.Expr{}
+						tmp_obj := g.new_tmp_var()
+						tmp_objs << tmp_obj
+						el_stype := g.typ(g.table.mktyp(expr.right_type))
+						g.writeln('$el_stype $tmp_obj;')
+					}
 					is_push << true
 				}
 				ast.AssignStmt {
@@ -2858,7 +2870,7 @@ fn (mut g Gen) select_expr(node ast.SelectExpr) {
 			g.writeln('-1) {')
 		} else {
 			g.writeln('$i) {')
-			if tmp_objs[i] != '' {
+			if !is_push[i] && tmp_objs[i] != '' {
 				g.write('\t${elem_types[i]}')
 				g.expr(objs[i])
 				g.writeln(' = ${tmp_objs[i]};')
diff --git a/vlib/v/parser/if_match.v b/vlib/v/parser/if_match.v
index ca51bc0d27..d635c9cf54 100644
--- a/vlib/v/parser/if_match.v
+++ b/vlib/v/parser/if_match.v
@@ -358,6 +358,7 @@ fn (mut p Parser) select_expr() ast.SelectExpr {
 			}
 		} else {
 			p.inside_match = true
+			p.inside_select = true
 			exprs, comments := p.expr_list()
 			if exprs.len != 1 {
 				p.error('only one expression allowed as `select` key')
@@ -373,6 +374,7 @@ fn (mut p Parser) select_expr() ast.SelectExpr {
 				}
 			}
 			p.inside_match = false
+			p.inside_select = false
 			match stmt {
 				ast.ExprStmt {
 					if !stmt.is_expr {
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 7775adc0c5..f964b805fa 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -47,6 +47,7 @@ mut:
 	is_amp            bool // for generating the right code for `&Foo{}`
 	returns           bool
 	inside_match      bool // to separate `match A { }` from `Struct{}`
+	inside_select     bool // to allow `ch <- Struct{} {` inside `select`
 	inside_match_case bool // to separate `match_expr { }` from `Struct{}`
 	inside_match_body bool // to fix eval not used TODO
 	inside_unsafe     bool
@@ -920,6 +921,7 @@ pub fn (mut p Parser) parse_ident(language table.Language) ast.Ident {
 }
 
 pub fn (mut p Parser) name_expr() ast.Expr {
+	prev_tok_kind := p.prev_tok.kind
 	mut node := ast.Expr{}
 	if p.expecting_type {
 		p.expecting_type = false
@@ -1073,7 +1075,8 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 		}
 	} else if (p.peek_tok.kind == .lcbr ||
 		(p.peek_tok.kind == .lt && lit0_is_capital)) &&
-		!p.inside_match && !p.inside_match_case && !p.inside_if && !p.inside_for { // && (p.tok.lit[0].is_capital() || p.builtin_mod) {
+		(!p.inside_match || (p.inside_select && prev_tok_kind == .arrow && lit0_is_capital)) && !p.inside_match_case &&
+		!p.inside_if && !p.inside_for { // && (p.tok.lit[0].is_capital() || p.builtin_mod) {
 		return p.struct_init(false) // short_syntax: false
 	} else if p.peek_tok.kind == .dot && (lit0_is_capital && !known_var && language == .v) {
 		// `Color.green`