From b677ad9ca5bbcb7cd7c0e1e6c91fceb62f6b125b Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Sat, 10 Oct 2020 14:42:40 +0100
Subject: [PATCH] checker: fix panic on match expression without results
 (#6597)

---
 vlib/v/checker/checker.v                 |  4 ++-
 vlib/v/checker/tests/if_match_result.out | 34 ++++++++++++++++++++++++
 vlib/v/checker/tests/if_match_result.vv  | 19 +++++++++++++
 3 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/if_match_result.out
 create mode 100644 vlib/v/checker/tests/if_match_result.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index f0c0dc8426..116038f63d 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3062,12 +3062,13 @@ pub fn (mut c Checker) match_expr(mut node ast.MatchExpr) table.Type {
 	mut branch_without_return := false
 	for branch in node.branches {
 		c.stmts(branch.stmts)
-		if node.is_expr {
+		if node.is_expr && branch.stmts.len > 0 {
 			// ignore last statement - workaround
 			// currently the last statement in a match branch does not have an
 			// expected value set, so e.g. IfExpr.is_expr is not set.
 			// probably any mismatch will be caught by not producing a value instead
 			for st in branch.stmts[0..branch.stmts.len - 1] {
+				// must not contain C statements
 				st.check_c_expr() or {
 					c.error('`match` expression branch has $err', st.position())
 				}
@@ -3476,6 +3477,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 					branch.pos)
 			}
 			for st in branch.stmts {
+				// must not contain C statements
 				st.check_c_expr() or {
 					c.error('`if` expression branch has $err', st.position())
 				}
diff --git a/vlib/v/checker/tests/if_match_result.out b/vlib/v/checker/tests/if_match_result.out
new file mode 100644
index 0000000000..53a154ea2f
--- /dev/null
+++ b/vlib/v/checker/tests/if_match_result.out
@@ -0,0 +1,34 @@
+vlib/v/checker/tests/if_match_result.vv:2:3: error: assignment mismatch: 1 variable(s) 0 value(s)
+    1 | // missing results
+    2 | _ = match 4 {
+      |   ^
+    3 |     1 {}
+    4 |     else {}
+vlib/v/checker/tests/if_match_result.vv:6:5: error: `if` expression requires an expression as the last statement of every branch
+    4 |     else {}
+    5 | }
+    6 | _ = if true {
+      |     ~~~~~~~
+    7 | } else {
+    8 | }
+vlib/v/checker/tests/if_match_result.vv:7:3: error: `if` expression requires an expression as the last statement of every branch
+    5 | }
+    6 | _ = if true {
+    7 | } else {
+      |   ~~~~
+    8 | }
+    9 |
+vlib/v/checker/tests/if_match_result.vv:11:3: error: assignment mismatch: 1 variable(s) 0 value(s)
+    9 |
+   10 | // void results
+   11 | _ = match 4 {
+      |   ^
+   12 |     1 {println('')}
+   13 |     else {exit(0)}
+vlib/v/checker/tests/if_match_result.vv:15:3: error: assignment mismatch: 1 variable(s) 0 value(s)
+   13 |     else {exit(0)}
+   14 | }
+   15 | _ = if true {
+      |   ^
+   16 |     println('')
+   17 | } else {
diff --git a/vlib/v/checker/tests/if_match_result.vv b/vlib/v/checker/tests/if_match_result.vv
new file mode 100644
index 0000000000..ad85b13bcc
--- /dev/null
+++ b/vlib/v/checker/tests/if_match_result.vv
@@ -0,0 +1,19 @@
+// missing results
+_ = match 4 {
+	1 {}
+	else {}
+}
+_ = if true {
+} else {
+}
+
+// void results
+_ = match 4 {
+	1 {println('')}
+	else {exit(0)}
+}
+_ = if true {
+	println('')
+} else {
+	exit(0)
+}