From 0b843b801f030f8727c73c4d7b318525c3383f95 Mon Sep 17 00:00:00 2001
From: ChAoS_UnItY <minecraft.kyle.train@gmail.com>
Date: Sat, 27 Aug 2022 14:00:14 +0800
Subject: [PATCH] checker: fix returning expression with void type (fix #15543)
 (#15554)

---
 vlib/builtin/cfns.c.v                    |  2 +-
 vlib/v/checker/if.v                      |  8 ++++++++
 vlib/v/checker/tests/if_match_result.out | 15 +++++++++++----
 vlib/v/checker/tests/if_match_result.vv  |  4 ++--
 4 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/vlib/builtin/cfns.c.v b/vlib/builtin/cfns.c.v
index 50b37f08a..f287f4d71 100644
--- a/vlib/builtin/cfns.c.v
+++ b/vlib/builtin/cfns.c.v
@@ -321,7 +321,7 @@ fn C.WriteConsole() voidptr
 
 fn C.WriteFile() voidptr
 
-fn C._wchdir(dirname &u16)
+fn C._wchdir(dirname &u16) int
 
 fn C._wgetcwd(buffer &u16, maxlen int) int
 
diff --git a/vlib/v/checker/if.v b/vlib/v/checker/if.v
index f3287636b..af9a11da5 100644
--- a/vlib/v/checker/if.v
+++ b/vlib/v/checker/if.v
@@ -194,6 +194,14 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 						node.typ = c.expected_type
 					}
 				}
+				if last_expr.typ == ast.void_type && !is_noreturn_callexpr(last_expr.expr)
+					&& !c.skip_flags {
+					// cannot return void type and use it as expr in any circumstances
+					// (e.g. argument expression, variable declaration / assignment)
+					c.error('the final expression in `if` or `match`, must have a value of a non-void type',
+						last_expr.pos)
+					continue
+				}
 				if !c.check_types(last_expr.typ, node.typ) {
 					if node.typ == ast.void_type {
 						// first branch of if expression
diff --git a/vlib/v/checker/tests/if_match_result.out b/vlib/v/checker/tests/if_match_result.out
index 53a154ea2..00c41ad1e 100644
--- a/vlib/v/checker/tests/if_match_result.out
+++ b/vlib/v/checker/tests/if_match_result.out
@@ -19,14 +19,21 @@ vlib/v/checker/tests/if_match_result.vv:7:3: error: `if` expression requires an
     8 | }
     9 |
 vlib/v/checker/tests/if_match_result.vv:11:3: error: assignment mismatch: 1 variable(s) 0 value(s)
-    9 |
+    9 | 
    10 | // void results
    11 | _ = match 4 {
       |   ^
-   12 |     1 {println('')}
-   13 |     else {exit(0)}
+   12 |     1 { println('') }
+   13 |     else { exit(0) }
+vlib/v/checker/tests/if_match_result.vv:16:2: error: the final expression in `if` or `match`, must have a value of a non-void type
+   14 | }
+   15 | _ = if true {
+   16 |     println('')
+      |     ~~~~~~~~~~~
+   17 | } else {
+   18 |     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)}
+   13 |     else { exit(0) }
    14 | }
    15 | _ = if true {
       |   ^
diff --git a/vlib/v/checker/tests/if_match_result.vv b/vlib/v/checker/tests/if_match_result.vv
index ad85b13bc..58cbda59c 100644
--- a/vlib/v/checker/tests/if_match_result.vv
+++ b/vlib/v/checker/tests/if_match_result.vv
@@ -9,8 +9,8 @@ _ = if true {
 
 // void results
 _ = match 4 {
-	1 {println('')}
-	else {exit(0)}
+	1 { println('') }
+	else { exit(0) }
 }
 _ = if true {
 	println('')
-- 
2.30.2