parser, checker: move more match validation from the parser into the …

…checker, add error for match without branches (#21181)

vlib/v/checker/match.v

@@ -535,17 +535,28 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 			}
 		}
 	}
+	if node.branches.len == 0 {
+		c.error('`match` must have at least two branches including `else`, or an exhaustive set of branches',
+			node.pos)
+		return
+	}
 	mut else_branch := node.branches.last()
-	mut has_else := else_branch.is_else
-	if !has_else {
-		for i, branch in node.branches {
-			if branch.is_else && i != node.branches.len - 1 {
-				c.error('`else` must be the last branch of `match`', branch.pos)
-				else_branch = branch
-				has_else = true
+	mut has_else, mut has_non_else := else_branch.is_else, !else_branch.is_else
+	for branch in node.branches[..node.branches.len - 1] {
+		if branch.is_else {
+			if has_else {
+				c.error('`match` can have only one `else` branch', branch.pos)
 			}
+			c.error('`else` must be the last branch of `match`', branch.pos)
+			else_branch = branch
+			has_else = true
+		} else {
+			has_non_else = true
 		}
 	}
+	if !has_non_else {
+		c.error('`match` must have at least one non `else` branch', else_branch.pos)
+	}
 	if is_exhaustive {
 		if has_else && !c.pref.translated && !c.file.is_translated {
 			c.error('match expression is exhaustive, `else` is unnecessary', else_branch.pos)

vlib/v/checker/tests/match_missing.out

@@ -0,0 +1,33 @@
+vlib/v/checker/tests/match_missing.vv:1:1: error: `match` must have at least two branches including `else`, or an exhaustive set of branches
+    1 | match true {
+      | ~~~~~
+    2 | }
+    3 |
+vlib/v/checker/tests/match_missing.vv:5:2: error: `match` can have only one `else` branch
+    3 | 
+    4 | match true {
+    5 |     else {}
+      |     ~~~~
+    6 |     else {}
+    7 | }
+vlib/v/checker/tests/match_missing.vv:5:2: error: `else` must be the last branch of `match`
+    3 | 
+    4 | match true {
+    5 |     else {}
+      |     ~~~~
+    6 |     else {}
+    7 | }
+vlib/v/checker/tests/match_missing.vv:5:2: error: `match` must have at least one non `else` branch
+    3 | 
+    4 | match true {
+    5 |     else {}
+      |     ~~~~
+    6 |     else {}
+    7 | }
+vlib/v/checker/tests/match_missing.vv:9:1: error: match must be exhaustive (add match branches for: `true`, `false` or `else {}` at the end)
+    7 | }
+    8 | 
+    9 | match true {
+      | ~~~~~~~~~~~~
+   10 |     'foo' == 'bar' {}
+   11 | }

vlib/v/checker/tests/match_missing.vv

@@ -0,0 +1,11 @@
+match true {
+}
+
+match true {
+	else {}
+	else {}
+}
+
+match true {
+	'foo' == 'bar' {}
+}

vlib/v/parser/if_match.v

@@ -237,7 +237,6 @@ fn (mut p Parser) is_match_sumtype_type() bool {
 
 fn (mut p Parser) match_expr() ast.MatchExpr {
 	match_first_pos := p.tok.pos()
-	mut else_count := 0
 	p.inside_match = true
 	p.check(.key_match)
 	mut is_sum_type := false
@@ -258,7 +257,6 @@ fn (mut p Parser) match_expr() ast.MatchExpr {
 		mut is_else := false
 		if p.tok.kind == .key_else {
 			is_else = true
-			else_count += 1
 			p.next()
 		} else if p.is_match_sumtype_type() || p.is_only_array_type()
 			|| p.tok.kind == .key_fn
@@ -289,6 +287,12 @@ fn (mut p Parser) match_expr() ast.MatchExpr {
 			}
 			is_sum_type = true
 		} else {
+			if p.tok.kind == .rcbr {
+				p.next()
+				return ast.MatchExpr{
+					pos: match_first_pos
+				}
+			}
 			// Expression match
 			for {
 				p.inside_match_case = true
@@ -351,12 +355,6 @@ fn (mut p Parser) match_expr() ast.MatchExpr {
 			post_comments: post_comments
 			scope: branch_scope
 		}
-		if is_else && branches.len == 1 {
-			p.error_with_pos('`match` must have at least one non `else` branch', pos)
-		}
-		if else_count > 1 {
-			p.error_with_pos('`match` can have only one `else` branch', pos)
-		}
 		if p.tok.kind == .rcbr || (is_else && no_lcbr) {
 			break
 		}