From 07a0a61875f4f5c7ac74acfd0c7dd4e4eb333dce Mon Sep 17 00:00:00 2001
From: Araq <rumpf_a@web.de>
Date: Tue, 29 Jan 2019 14:31:43 +0100
Subject: [PATCH] fixes #9149 [backport]

---
 lib/system.nim                          | 10 ++++++----
 tests/overload/tconverter_to_string.nim | 22 ++++++++++++++++++++++
 2 files changed, 28 insertions(+), 4 deletions(-)
 create mode 100644 tests/overload/tconverter_to_string.nim

diff --git a/lib/system.nim b/lib/system.nim
index 0241b92e08..4951961cac 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -4307,15 +4307,17 @@ proc `==`*(x, y: cstring): bool {.magic: "EqCString", noSideEffect,
 when defined(nimNoNilSeqs2):
   when not compileOption("nilseqs"):
     when defined(nimHasUserErrors):
-      proc `==`*(x: string; y: type(nil)): bool {.
+      # bug #9149; ensure that 'type(nil)' does not match *too* well by using 'type(nil) | type(nil)'.
+      # Eventually (in 0.20?) we will be able to remove this hack completely.
+      proc `==`*(x: string; y: type(nil) | type(nil)): bool {.
           error: "'nil' is now invalid for 'string'; compile with --nilseqs:on for a migration period".} =
         discard
-      proc `==`*(x: type(nil); y: string): bool {.
+      proc `==`*(x: type(nil) | type(nil); y: string): bool {.
           error: "'nil' is now invalid for 'string'; compile with --nilseqs:on for a migration period".} =
         discard
     else:
-      proc `==`*(x: string; y: type(nil)): bool {.error.} = discard
-      proc `==`*(x: type(nil); y: string): bool {.error.} = discard
+      proc `==`*(x: string; y: type(nil) | type(nil)): bool {.error.} = discard
+      proc `==`*(x: type(nil) | type(nil); y: string): bool {.error.} = discard
 
 template closureScope*(body: untyped): untyped =
   ## Useful when creating a closure in a loop to capture local loop variables by
diff --git a/tests/overload/tconverter_to_string.nim b/tests/overload/tconverter_to_string.nim
new file mode 100644
index 0000000000..1960372d8a
--- /dev/null
+++ b/tests/overload/tconverter_to_string.nim
@@ -0,0 +1,22 @@
+discard """
+  output: '''123
+c is not nil'''
+"""
+
+# bug #9149
+
+type
+  Container = ref object
+    data: int
+
+converter containerToString*(x: Container): string = $x.data
+
+var c = Container(data: 123)
+var str = string c
+echo str
+
+if c == nil: # this line can compile on v0.18, but not on 0.19
+  echo "c is nil"
+
+if not c.isNil:
+  echo "c is not nil"