nixpkgs/pkgs/development/compilers/nim/nixbuild.patch

diff --git a/lib/pure/dynlib.nim b/lib/pure/dynlib.nim
index f31ae94dd..debed9c07 100644
--- a/lib/pure/dynlib.nim
+++ b/lib/pure/dynlib.nim
@@ -56,6 +56,9 @@
 
 import strutils
 
+when defined(nixbuild):
+  import os
+
 type
   LibHandle* = pointer ## a handle to a dynamically loaded library
 
@@ -95,6 +98,25 @@ proc libCandidates*(s: string, dest: var seq[string]) =
       libCandidates(prefix & middle & suffix, dest)
   else:
     add(dest, s)
+  when defined(nixbuild):
+    # Nix doesn't have a global library directory so
+    # load libraries using an absolute path if one
+    # can be derived from NIX_LDFLAGS.
+    #
+    # During Nix/NixOS packaging the line "define:nixbuild"
+    # should be appended to the ../../config/nim.cfg file
+    # to enable this behavior by default.
+    #
+    var libDirs = split(getEnv("LD_LIBRARY_PATH"), ':')
+    for flag in split(replace(getEnv("NIX_LDFLAGS"), "\\ ", " ")):
+      if flag.startsWith("-L"):
+        libDirs.add(flag[2..flag.high])
+    for lib in dest:
+      for dir in libDirs:
+        let abs = dir / lib
+        if existsFile(abs):
+          dest = @[abs]
+          return
 
 proc loadLibPattern*(pattern: string, globalSymbols = false): LibHandle =
   ## loads a library with name matching `pattern`, similar to what `dlimport`