From 4d50bc3f8dd2b9fd5b7dde6f63f104aaba6dbf5a Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sat, 23 Mar 2019 18:46:20 -0400
Subject: [PATCH] add peer type resolution for `*const T` and `?*T`

closes #1298
---
 doc/langref.html.in               |  7 +++++++
 src/ir.cpp                        | 17 +++++++++++++++++
 test/stage1/behavior/pointers.zig |  7 +++++++
 3 files changed, 31 insertions(+)

diff --git a/doc/langref.html.in b/doc/langref.html.in
index 0de6650c56..a9281b4918 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -4695,6 +4695,13 @@ fn peerTypeEmptyArrayAndSliceAndError(a: bool, slice: []u8) anyerror![]u8 {
 
     return slice[0..1];
 }
+
+test "peer type resolution: *const T and ?*T" {
+    const a = @intToPtr(*const usize, 0x123456789);
+    const b = @intToPtr(?*usize, 0x123456789);
+    assert(a == b);
+    assert(b == a);
+}
       {#code_end#}
       {#header_close#}
       {#header_close#}
diff --git a/src/ir.cpp b/src/ir.cpp
index f8301f0116..54b567efe5 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -9658,6 +9658,23 @@ static ZigType *ir_resolve_peer_types(IrAnalyze *ira, AstNode *source_node, ZigT
             continue;
         }
 
+        if (prev_type->id == ZigTypeIdOptional &&
+            types_match_const_cast_only(ira, cur_type, prev_type->data.maybe.child_type,
+                source_node, false).id == ConstCastResultIdOk)
+        {
+            prev_inst = cur_inst;
+            any_are_null = true;
+            continue;
+        }
+
+        if (cur_type->id == ZigTypeIdOptional &&
+            types_match_const_cast_only(ira, prev_type, cur_type->data.maybe.child_type,
+                source_node, false).id == ConstCastResultIdOk)
+        {
+            any_are_null = true;
+            continue;
+        }
+
         if (cur_type->id == ZigTypeIdUndefined) {
             continue;
         }
diff --git a/test/stage1/behavior/pointers.zig b/test/stage1/behavior/pointers.zig
index 1bb23866b4..5b73cd98df 100644
--- a/test/stage1/behavior/pointers.zig
+++ b/test/stage1/behavior/pointers.zig
@@ -130,3 +130,10 @@ test "initialize const optional C pointer to null" {
     expect(a == null);
     comptime expect(a == null);
 }
+
+test "compare equality of optional and non-optional pointer" {
+    const a = @intToPtr(*const usize, 0x123456789);
+    const b = @intToPtr(?*usize, 0x123456789);
+    expect(a == b);
+    expect(b == a);
+}