Add rebuild tests for plot_directive

The new tests:
 - make sure that unchanged plots are not recreated upon a second
   invocation of sphinx-build
 - make sure that plots with `:context:` are recreated (matplotlib#20523)
 - make sure that plots included via `.. include:` are updated when
   modified (matplotlib#17860)

Author: yongrenjie

lib/matplotlib/tests/test_sphinxext.py

@@ -5,6 +5,7 @@
 from pathlib import Path
 from subprocess import Popen, PIPE
 import sys
+import shutil
 
 import pytest
 
@@ -13,27 +14,21 @@
 
 
 def test_tinypages(tmpdir):
-    tmp_path = Path(tmpdir)
-    html_dir = tmp_path / 'html'
-    doctree_dir = tmp_path / 'doctrees'
-    # Build the pages with warnings turned into errors
-    cmd = [sys.executable, '-msphinx', '-W', '-b', 'html',
-           '-d', str(doctree_dir),
-           str(Path(__file__).parent / 'tinypages'), str(html_dir)]
-    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
-                 env={**os.environ, "MPLBACKEND": ""})
-    out, err = proc.communicate()
+    source_dir = Path(tmpdir) / 'src'
+    shutil.copytree(str(Path(__file__).parent / 'tinypages'), str(source_dir))
+    html_dir = source_dir / '_build' / 'html'
+    doctree_dir = source_dir / 'doctrees'
 
-    assert proc.returncode == 0, \
-        f"sphinx build failed with stdout:\n{out}\nstderr:\n{err}\n"
-    if err:
-        pytest.fail(f"sphinx build emitted the following warnings:\n{err}")
-
-    assert html_dir.is_dir()
+    # Build the pages with warnings turned into errors
+    build_sphinx_html(source_dir, doctree_dir, html_dir)
 
     def plot_file(num):
         return html_dir / f'some_plots-{num}.png'
 
+    def plot_directive_file(num):
+        # This is always next to the doctree dir.
+        return doctree_dir.parent / 'plot_directive' / f'some_plots-{num}.png'
+
     range_10, range_6, range_4 = [plot_file(i) for i in range(1, 4)]
     # Plot 5 is range(6) plot
     assert filecmp.cmp(range_6, plot_file(5))
@@ -48,6 +43,7 @@ def plot_file(num):
     assert filecmp.cmp(range_4, plot_file(13))
     # Plot 14 has included source
     html_contents = (html_dir / 'some_plots.html').read_bytes()
+
     assert b'# Only a comment' in html_contents
     # check plot defined in external file.
     assert filecmp.cmp(range_4, html_dir / 'range4.png')
@@ -62,3 +58,47 @@ def plot_file(num):
     assert b'plot-directive my-class my-other-class' in html_contents
     # check that the multi-image caption is applied twice
     assert html_contents.count(b'This caption applies to both plots.') == 2
+    # Plot 21 is range(6) plot via an include directive. But because some of
+    # the previous plots are repeated, the argument to plot_file() is only 17.
+    assert filecmp.cmp(range_6, plot_file(17))
+
+    # Modify the included plot
+    with open(str(source_dir / 'included_plot_21.rst'), 'r') as file:
+        contents = file.read()
+    contents = contents.replace('plt.plot(range(6))', 'plt.plot(range(4))')
+    with open(str(source_dir / 'included_plot_21.rst'), 'w') as file:
+        file.write(contents)
+    # Build the pages again and check that the modified file was updated
+    modification_times = [plot_directive_file(i).stat().st_mtime
+                          for i in (1, 2, 3, 5)]
+    build_sphinx_html(source_dir, doctree_dir, html_dir)
+    assert filecmp.cmp(range_4, plot_file(17))
+    # Check that the plots in the plot_directive folder weren't changed.
+    # (plot_directive_file(1) won't be modified, but it will be copied to html/
+    # upon compilation, so plot_file(1) will be modified)
+    assert plot_directive_file(1).stat().st_mtime == modification_times[0]
+    assert plot_directive_file(2).stat().st_mtime == modification_times[1]
+    assert plot_directive_file(3).stat().st_mtime == modification_times[2]
+    assert filecmp.cmp(range_10, plot_file(1))
+    assert filecmp.cmp(range_6, plot_file(2))
+    assert filecmp.cmp(range_4, plot_file(3))
+    # Make sure that figures marked with context are re-created (but that the
+    # contents are the same)
+    assert plot_directive_file(5).stat().st_mtime > modification_times[3]
+    assert filecmp.cmp(range_6, plot_file(5))
+
+
+def build_sphinx_html(source_dir, doctree_dir, html_dir):
+    # Build the pages with warnings turned into errors
+    cmd = [sys.executable, '-msphinx', '-W', '-b', 'html',
+           '-d', str(doctree_dir), str(source_dir), str(html_dir)]
+    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
+                 env={**os.environ, "MPLBACKEND": ""})
+    out, err = proc.communicate()
+
+    assert proc.returncode == 0, \
+        f"sphinx build failed with stdout:\n{out}\nstderr:\n{err}\n"
+    if err:
+        pytest.fail(f"sphinx build emitted the following warnings:\n{err}")
+
+    assert html_dir.is_dir()

lib/matplotlib/tests/tinypages/included_plot_21.rst

@@ -0,0 +1,6 @@
+Plot 21 has length 6
+
+.. plot::
+
+    plt.plot(range(6))
+

lib/matplotlib/tests/tinypages/some_plots.rst

@@ -166,3 +166,8 @@ scenario:
 
    plt.figure()
    plt.plot(range(4))
+ 
+Plot 21 is generated via an include directive:
+
+.. include:: included_plot_21.rst
+