From 7e2ec8f8a15b77c14c185c4044e99ba05e8b6a38 Mon Sep 17 00:00:00 2001
From: rnhmjoj <rnhmjoj@inventati.org>
Date: Wed, 26 May 2021 01:24:27 +0200
Subject: [PATCH] pythonPackages.matplotlib: fix headless detection

The default backend is chosen based on the content of the $DISPLAY
variable *and* a successfull call to libX11, loaded via dlopen().
The test fails because dlopen looks in /usr/lib and /lib, so matplotlib
falls back to a headless backend.

To reproduce try running:

    $ nix-shell -I nixpkgs=$PWD -p \
      'python3.withPackages (p: [ p.matplotlib ])' --run python
    >>> import matplotlib.pyplot as plt
    >>> assert plt.get_backend() == "TkAgg"
---
 .../python-modules/matplotlib/default.nix      | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/pkgs/development/python-modules/matplotlib/default.nix b/pkgs/development/python-modules/matplotlib/default.nix
index 7364920cba2..192ecf2fae0 100644
--- a/pkgs/development/python-modules/matplotlib/default.nix
+++ b/pkgs/development/python-modules/matplotlib/default.nix
@@ -5,12 +5,18 @@
 , enableGhostscript ? true, ghostscript, gtk3
 , enableGtk3 ? false, cairo
 # darwin has its own "MacOSX" backend
-, enableTk ? !stdenv.isDarwin, tcl, tk, tkinter, libX11
+, enableTk ? !stdenv.isDarwin, tcl, tk, tkinter
 , enableQt ? false, pyqt5
+# required for headless detection
+, libX11, wayland
 , Cocoa
 , pythonOlder
 }:
 
+let
+  interactive = enableTk || enableGtk3 || enableQt;
+in
+
 buildPythonPackage rec {
   version = "3.4.1";
   pname = "matplotlib";
@@ -62,8 +68,14 @@ buildPythonPackage rec {
     let
       tcl_tk_cache = ''"${tk}/lib", "${tcl}/lib", "${lib.strings.substring 0 3 tk.version}"'';
     in
-    lib.optionalString enableTk
-      "sed -i '/self.tcl_tk_cache = None/s|None|${tcl_tk_cache}|' setupext.py";
+    lib.optionalString enableTk ''
+      sed -i '/self.tcl_tk_cache = None/s|None|${tcl_tk_cache}|' setupext.py
+    '' + lib.optionalString (stdenv.isLinux && interactive) ''
+      # fix paths to libraries in dlopen calls (headless detection)
+      substituteInPlace src/_c_internal_utils.c \
+        --replace libX11.so.6 ${libX11}/lib/libX11.so.6 \
+        --replace libwayland-client.so.0 ${wayland}/lib/libwayland-client.so.0
+    '';
 
   # Matplotlib needs to be built against a specific version of freetype in
   # order for all of the tests to pass.