From 12e48c6fe25dfb293706a2b9fc344813458b5ece Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20D=C3=A4schle?= <daniel.daeschle@gmail.com>
Date: Tue, 14 Apr 2020 01:03:31 +0200
Subject: [PATCH] checker: check match for exhaustion

---
 vlib/v/ast/ast.v                              |  1 +
 vlib/v/checker/checker.v                      | 12 ++++++++++
 .../v/checker/tests/inout/match_expr_else.out |  7 ++++++
 vlib/v/checker/tests/inout/match_expr_else.vv | 13 ++++++++++
 vlib/v/fmt/fmt.v                              |  2 +-
 vlib/v/gen/cgen.v                             |  6 ++---
 vlib/v/parser/parser.v                        | 24 +++++++++++++------
 vlib/v/util/errors.v                          |  4 +++-
 8 files changed, 57 insertions(+), 12 deletions(-)
 create mode 100644 vlib/v/checker/tests/inout/match_expr_else.out
 create mode 100644 vlib/v/checker/tests/inout/match_expr_else.vv

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 904170faaf..454e9a36a4 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -399,6 +399,7 @@ pub:
 	stmts   []Stmt
 	pos     token.Position
 	comment Comment // comment above `xxx {`
+	is_else bool
 }
 
 pub struct CompIf {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 94aa8941d7..642300b190 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1323,6 +1323,18 @@ pub fn (c mut Checker) match_expr(node mut ast.MatchExpr) table.Type {
 	if cond_type == 0 {
 		c.error('match 0 cond type', node.pos)
 	}
+	// check for exhaustion when match is expr
+	if node.is_sum_type && node.is_expr && !node.branches[node.branches.len - 1].is_else {
+		type_sym := c.table.get_type_symbol(cond_type)
+		info := type_sym.info as table.SumType
+		mut used_sum_types_count := 0
+		for branch in node.branches {
+			used_sum_types_count += branch.exprs.len
+		}
+		if used_sum_types_count < info.variants.len {
+			c.error('match must be exhaustive', node.pos)
+		}
+	}
 	c.expected_type = cond_type
 	mut ret_type := table.void_type
 	for branch in node.branches {
diff --git a/vlib/v/checker/tests/inout/match_expr_else.out b/vlib/v/checker/tests/inout/match_expr_else.out
new file mode 100644
index 0000000000..3ac1bbf9cc
--- /dev/null
+++ b/vlib/v/checker/tests/inout/match_expr_else.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/inout/match_expr_else.v:5:9: error: match must be exhaustive
+    3| fn main() {
+    4|     x := A('test')
+    5|     res := match x {
+                  ~~~~~~~~~
+    6|         int {
+    7|             'int'
\ No newline at end of file
diff --git a/vlib/v/checker/tests/inout/match_expr_else.vv b/vlib/v/checker/tests/inout/match_expr_else.vv
new file mode 100644
index 0000000000..d32dabd9f2
--- /dev/null
+++ b/vlib/v/checker/tests/inout/match_expr_else.vv
@@ -0,0 +1,13 @@
+type A = int | string | f64
+
+fn main() {
+	x := A('test')
+	res := match x {
+		int {
+			'int'
+		}
+		string {
+			'string'
+		}
+	}
+}
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index b4469c5c93..44e144b603 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -577,7 +577,7 @@ fn (f mut Fmt) expr(node ast.Expr) {
 				if branch.comment.text != '' {
 					f.comment(branch.comment)
 				}
-				if i < it.branches.len - 1 {
+				if !branch.is_else {
 					// normal branch
 					for j, expr in branch.exprs {
 						f.expr(expr)
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 1a93f72128..24a1cfd25e 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -1373,8 +1373,8 @@ fn (g mut Gen) match_expr(node ast.MatchExpr) {
 	// g.writeln(';') // $it.blocks.len')
 	// mut sum_type_str = ''
 	for j, branch in node.branches {
-		if j == node.branches.len - 1 {
-			// last block is an `else{}`
+		is_last := j == node.branches.len - 1
+		if branch.is_else || node.is_expr && is_last {
 			if node.branches.len > 1 {
 				if is_expr {
 					// TODO too many branches. maybe separate ?: matches
@@ -1447,7 +1447,7 @@ fn (g mut Gen) match_expr(node ast.MatchExpr) {
 		}
 		g.stmts(branch.stmts)
 		if !g.inside_ternary && node.branches.len > 1 {
-			g.writeln('}')
+			g.write('}')
 		}
 	}
 	g.inside_ternary = was_inside_ternary
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 7aaeff0876..b16ee45a7d 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1834,8 +1834,8 @@ fn (p mut Parser) global_decl() ast.GlobalDecl {
 }
 
 fn (p mut Parser) match_expr() ast.MatchExpr {
+	match_first_pos := p.tok.position()
 	p.check(.key_match)
-	pos := p.tok.position()
 	is_mut := p.tok.kind == .key_mut
 	mut is_sum_type := false
 	if is_mut {
@@ -1844,15 +1844,15 @@ fn (p mut Parser) match_expr() ast.MatchExpr {
 	cond := p.expr(0)
 	p.check(.lcbr)
 	mut branches := []ast.MatchBranch
-	mut have_final_else := false
 	for {
+		branch_first_pos := p.tok.position()
 		comment := p.check_comment()		// comment before {}
 		mut exprs := []ast.Expr
-		branch_pos := p.tok.position()
 		p.open_scope()
 		// final else
+		mut is_else := false
 		if p.tok.kind == .key_else {
-			have_final_else = true
+			is_else = true
 			p.next()
 		} else if p.tok.kind == .name && (p.tok.lit in table.builtin_type_names ||
 				(p.tok.lit[0].is_capital() && !p.tok.lit.is_upper()) || p.peek_tok.kind == .dot) {
@@ -1890,21 +1890,31 @@ fn (p mut Parser) match_expr() ast.MatchExpr {
 				p.check(.comma)
 			}
 		}
+		branch_last_pos := p.tok.position()
 		// p.warn('match block')
 		stmts := p.parse_block()
+		pos := token.Position{
+			line_nr: match_first_pos.line_nr
+			pos: match_first_pos.pos
+			len: branch_last_pos.pos - branch_first_pos.pos + branch_last_pos.len
+		}
 		branches << ast.MatchBranch{
 			exprs: exprs
 			stmts: stmts
-			pos: branch_pos
+			pos: pos
 			comment: comment
+			is_else: is_else
 		}
 		p.close_scope()
 		if p.tok.kind == .rcbr {
 			break
 		}
 	}
-	if !have_final_else {
-		p.error('match must be exhaustive')
+	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
 	}
 	p.check(.rcbr)
 	return ast.MatchExpr{
diff --git a/vlib/v/util/errors.v b/vlib/v/util/errors.v
index 32c90b4adb..623043dce9 100644
--- a/vlib/v/util/errors.v
+++ b/vlib/v/util/errors.v
@@ -96,7 +96,9 @@ pub fn formatted_error(kind string /*error or warn*/, emsg string, filepath stri
 					continue
 				}
 				if pos.len > 1 {
-					underline := '~'.repeat(pos.len)
+					max_len := sline.len - pointerline.len // rest of the line
+					len := if pos.len > max_len { max_len } else { pos.len }
+					underline := '~'.repeat(len)
 					pointerline << if emanager.support_color { term.bold(term.blue(underline)) } else { underline }
 				}else{
 					pointerline << if emanager.support_color { term.bold(term.blue('^')) } else { '^' }