From 3919afcad26d2359efe52f98cd4f2f0573527369 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <superjoe30@gmail.com>
Date: Fri, 9 Feb 2018 11:16:04 -0500
Subject: [PATCH] fix crash with error peer type resolution

closes #765
---
 src/ir.cpp           |  2 +-
 test/cases/error.zig | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/ir.cpp b/src/ir.cpp
index 5f7e02848ad96115c8ee9cca07563a1bd98e6911..61c26cb5ae2579d5fab6bbce187d7c3acec22ffd 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -7279,7 +7279,7 @@ static TypeTableEntry *ir_resolve_peer_types(IrAnalyze *ira, AstNode *source_nod
                     prev_inst = cur_inst;
                 }
 
-                TypeTableEntry *prev_err_set_type = prev_type->data.error_union.err_set_type;
+                TypeTableEntry *prev_err_set_type = (err_set_type == nullptr) ? prev_type->data.error_union.err_set_type : err_set_type;
                 TypeTableEntry *cur_err_set_type = cur_type->data.error_union.err_set_type;
 
                 if (!resolve_inferred_error_set(ira, prev_err_set_type, cur_inst->source_node)) {
diff --git a/test/cases/error.zig b/test/cases/error.zig
index bb1366429bebaa309a494929aede206d07ffe5f2..e64bf02c9147d750c1d01697490edb493c48ea9d 100644
--- a/test/cases/error.zig
+++ b/test/cases/error.zig
@@ -150,3 +150,28 @@ fn testErrToIntWithOnePossibleValue(x: error{A}, comptime value: u32) void {
         @compileError("bad");
     }
 }
+
+test "error union peer type resolution" {
+    testErrorUnionPeerTypeResolution(1);
+    comptime testErrorUnionPeerTypeResolution(1);
+}
+
+fn testErrorUnionPeerTypeResolution(x: i32) void {
+    const y = switch (x) {
+        1 => bar_1(),
+        2 => baz_1(),
+        else => quux_1(),
+    };
+}
+
+fn bar_1() error {
+    return error.A;
+}
+
+fn baz_1() !i32 {
+    return error.B;
+}
+
+fn quux_1() !i32 {
+    return error.C;
+}
-- 
2.54.0