From ffa1669c5847cba6ab14383083af00a9d830c40d Mon Sep 17 00:00:00 2001
From: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
Date: Sun, 29 Mar 2020 04:19:02 +0200
Subject: [PATCH] Backport PR #16949: TST: Don't modify actual pyplot file for
 boilerplate test.

---
 lib/matplotlib/tests/test_pyplot.py | 43 +++++++++++++++--------------
 tools/boilerplate.py                | 11 +++++---
 2 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/lib/matplotlib/tests/test_pyplot.py b/lib/matplotlib/tests/test_pyplot.py
index e4860aa2117f..51470d2bf1b5 100644
--- a/lib/matplotlib/tests/test_pyplot.py
+++ b/lib/matplotlib/tests/test_pyplot.py
@@ -9,31 +9,32 @@
 from matplotlib import pyplot as plt
 
 
-def test_pyplot_up_to_date():
+def test_pyplot_up_to_date(tmpdir):
     gen_script = Path(mpl.__file__).parents[2] / "tools/boilerplate.py"
     if not gen_script.exists():
         pytest.skip("boilerplate.py not found")
     orig_contents = Path(plt.__file__).read_text()
-    try:
-        subprocess.run([sys.executable, str(gen_script)], check=True)
-        new_contents = Path(plt.__file__).read_text()
-
-        if orig_contents != new_contents:
-            diff_msg = '\n'.join(
-                difflib.unified_diff(
-                    orig_contents.split('\n'), new_contents.split('\n'),
-                    fromfile='found pyplot.py',
-                    tofile='expected pyplot.py',
-                    n=0, lineterm=''))
-            pytest.fail(
-                "pyplot.py is not up-to-date. Please run "
-                "'python tools/boilerplate.py' to update pyplot.py. "
-                "This needs to be done from an environment where your "
-                "current working copy is installed (e.g. 'pip install -e'd). "
-                "Here is a diff of unexpected differences:\n%s" % diff_msg
-            )
-    finally:
-        Path(plt.__file__).write_text(orig_contents)
+    plt_file = tmpdir.join('pyplot.py')
+    plt_file.write_text(orig_contents, 'utf-8')
+
+    subprocess.run([sys.executable, str(gen_script), str(plt_file)],
+                   check=True)
+    new_contents = plt_file.read_text('utf-8')
+
+    if orig_contents != new_contents:
+        diff_msg = '\n'.join(
+            difflib.unified_diff(
+                orig_contents.split('\n'), new_contents.split('\n'),
+                fromfile='found pyplot.py',
+                tofile='expected pyplot.py',
+                n=0, lineterm=''))
+        pytest.fail(
+            "pyplot.py is not up-to-date. Please run "
+            "'python tools/boilerplate.py' to update pyplot.py. "
+            "This needs to be done from an environment where your "
+            "current working copy is installed (e.g. 'pip install -e'd). "
+            "Here is a diff of unexpected differences:\n%s" % diff_msg
+        )
 
 
 def test_pyplot_box():
diff --git a/tools/boilerplate.py b/tools/boilerplate.py
index caec5247410e..faf6927da742 100644
--- a/tools/boilerplate.py
+++ b/tools/boilerplate.py
@@ -16,6 +16,7 @@
 import inspect
 from inspect import Parameter
 from pathlib import Path
+import sys
 import textwrap
 
 # This line imports the installed copy of matplotlib, and not the local copy.
@@ -327,9 +328,7 @@ def boilerplate_gen():
     yield '_setup_pyplot_info_docstrings()'
 
 
-def build_pyplot():
-    pyplot_path = Path(__file__).parent / "../lib/matplotlib/pyplot.py"
-
+def build_pyplot(pyplot_path):
     pyplot_orig = pyplot_path.read_text().splitlines(keepends=True)
     try:
         pyplot_orig = pyplot_orig[:pyplot_orig.index(PYPLOT_MAGIC_HEADER) + 1]
@@ -345,4 +344,8 @@ def build_pyplot():
 
 if __name__ == '__main__':
     # Write the matplotlib.pyplot file.
-    build_pyplot()
+    if len(sys.argv) > 1:
+        pyplot_path = Path(sys.argv[1])
+    else:
+        pyplot_path = Path(__file__).parent / "../lib/matplotlib/pyplot.py"
+    build_pyplot(pyplot_path)