From 9bf512b52716435337aba29b07a42af28d71c8fe Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Wed, 14 Nov 2018 10:39:56 +0100
Subject: [PATCH] Don't insert spurious newlines by joining tex.preamble.

The rc validator already makes it a single string.

Also reject non-strings in the validator, as there isn't much use to
them anyways in this context.
---
 ...cparams-pgf.preamble-full-LaTeX-support.rst |  2 ++
 lib/matplotlib/rcsetup.py                      | 18 +++++++++---------
 lib/matplotlib/texmanager.py                   |  2 +-
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/doc/api/next_api_changes/2018-10-30-rcparams-pgf.preamble-full-LaTeX-support.rst b/doc/api/next_api_changes/2018-10-30-rcparams-pgf.preamble-full-LaTeX-support.rst
index 892130589744..9e27f67c38fd 100644
--- a/doc/api/next_api_changes/2018-10-30-rcparams-pgf.preamble-full-LaTeX-support.rst
+++ b/doc/api/next_api_changes/2018-10-30-rcparams-pgf.preamble-full-LaTeX-support.rst
@@ -9,3 +9,5 @@ The parsing has been modified to pass the complete line to the LaTeX system,
 keeping all commas.
 
 Passing a list of strings from within a Python script still works as it used to.
+
+Passing a list containing non-strings now fails, instead of coercing the results to strings.
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 488d4304edd1..f054fa9e694f 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -175,17 +175,17 @@ def validate_string_or_None(s):
         raise ValueError('Could not convert "%s" to string' % s)
 
 
-def _validate_stringlist_or_string(s):
-    """convert s to string or raise"""
+def _validate_tex_preamble(s):
     if s is None or s == 'None':
         return ""
     try:
         if isinstance(s, str):
             return s
-        if isinstance(s, Iterable):
-            return '\n'.join([str(i) for i in s])
-        raise ValueError()
-    except ValueError:
+        elif isinstance(s, Iterable):
+            return '\n'.join(s)
+        else:
+            raise TypeError
+    except TypeError:
         raise ValueError('Could not convert "%s" to string' % s)
 
 
@@ -412,7 +412,7 @@ def validate_color(s):
 
 
 def validate_string(s):
-    if isinstance(s, (str, str)):
+    if isinstance(s, str):
         # Always leave str as str and unicode as unicode
         return s
     else:
@@ -1129,7 +1129,7 @@ def _validate_linestyle(ls):
     'text.color':          ['black', validate_color],
     'text.usetex':         [False, validate_bool],
     'text.latex.unicode':  [True, validate_bool],
-    'text.latex.preamble': ['', _validate_stringlist_or_string],
+    'text.latex.preamble': ['', _validate_tex_preamble],
     'text.latex.preview':  [False, validate_bool],
     'text.dvipnghack':     [None, validate_bool_maybe_none],
     'text.hinting':        ['auto', validate_hinting],
@@ -1405,7 +1405,7 @@ def _validate_linestyle(ls):
     # use matplotlib rc settings for font configuration
     'pgf.rcfonts':   [True, validate_bool],
     # provide a custom preamble for the latex process
-    'pgf.preamble':  ['', _validate_stringlist_or_string],
+    'pgf.preamble':  ['', _validate_tex_preamble],
 
     # write raster image data directly into the svg file
     'svg.image_inline':     [True, validate_bool],
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
index 0f61dbdca441..3841be4ecad4 100644
--- a/lib/matplotlib/texmanager.py
+++ b/lib/matplotlib/texmanager.py
@@ -181,7 +181,7 @@ def get_font_preamble(self):
 
     def get_custom_preamble(self):
         """Return a string containing user additions to the tex preamble."""
-        return '\n'.join(rcParams['text.latex.preamble'])
+        return rcParams['text.latex.preamble']
 
     def make_tex(self, tex, fontsize):
         """