Fix #4362: latex: Don't overwrite .tex file if document not changed

CHANGES

@@ -137,6 +137,7 @@ Features added
 * html: Output ``canonical_url`` metadata if :confval:`html_baseurl` set (refs:
   #4193)
 * #5029: autosummary: expose ``inherited_members`` to template
+* #4362: latex: Don't overwrite .tex file if document not changed
 
 Bugs fixed
 ----------

sphinx/builders/latex/__init__.py

@@ -13,7 +13,6 @@ import os
 from os import path
 
 from docutils.frontend import OptionParser
-from docutils.io import FileOutput
 from six import text_type
 
 from sphinx import package_dir, addnodes, highlighting
@@ -31,7 +30,7 @@ from sphinx.locale import _, __
 from sphinx.transforms import SphinxTransformer
 from sphinx.util import texescape, logging, status_iterator
 from sphinx.util.console import bold, darkgreen  # type: ignore
-from sphinx.util.docutils import new_document
+from sphinx.util.docutils import SphinxFileOutput, new_document
 from sphinx.util.fileutil import copy_asset_file
 from sphinx.util.nodes import inline_all_toctrees
 from sphinx.util.osutil import SEP, make_filename
@@ -134,9 +133,8 @@ class LaTeXBuilder(Builder):
             toctree_only = False
             if len(entry) > 5:
                 toctree_only = entry[5]
-            destination = FileOutput(
-                destination_path=path.join(self.outdir, targetname),
-                encoding='utf-8')
+            destination = SphinxFileOutput(destination_path=path.join(self.outdir, targetname),
+                                           encoding='utf-8', overwrite_if_changed=True)
             logger.info(__("processing %s..."), targetname, nonl=1)
             toctrees = self.env.get_doctree(docname).traverse(addnodes.toctree)
             if toctrees:

sphinx/util/docutils.py

@@ -10,6 +10,7 @@
 """
 from __future__ import absolute_import
 
+import codecs
 import os
 import re
 import types
@@ -21,6 +22,7 @@ from os import path
 
 import docutils
 from docutils import nodes
+from docutils.io import FileOutput
 from docutils.parsers.rst import Directive, directives, roles, convert_directive_function
 from docutils.statemachine import StateMachine
 from docutils.utils import Reporter
@@ -300,6 +302,26 @@ def switch_source_input(state, content):
         state.memo.reporter.get_source_and_line = get_source_and_line
 
 
+class SphinxFileOutput(FileOutput):
+    """Better FileOutput class for Sphinx."""
+
+    def __init__(self, **kwargs):
+        # type: (Any) -> None
+        self.overwrite_if_changed = kwargs.pop('overwrite_if_changed', False)
+        FileOutput.__init__(self, **kwargs)
+
+    def write(self, data):
+        # type: (unicode) -> unicode
+        if (self.destination_path and self.autoclose and 'b' not in self.mode and
+                self.overwrite_if_changed and os.path.exists(self.destination_path)):
+            with codecs.open(self.destination_path, encoding=self.encoding) as f:
+                # skip writing: content not changed
+                if f.read() == data:
+                    return data
+
+        return FileOutput.write(self, data)
+
+
 class SphinxDirective(Directive):
     """A base class for Sphinx directives.
 

tests/test_util_docutils.py

@@ -9,9 +9,11 @@
     :license: BSD, see LICENSE for details.
 """
 
+import os
+
 from docutils import nodes
 
-from sphinx.util.docutils import docutils_namespace, register_node
+from sphinx.util.docutils import SphinxFileOutput, docutils_namespace, register_node
 
 
 def test_register_node():
@@ -32,3 +34,31 @@ def test_register_node():
     assert not hasattr(nodes.GenericNodeVisitor, 'depart_custom_node')
     assert not hasattr(nodes.SparseNodeVisitor, 'visit_custom_node')
     assert not hasattr(nodes.SparseNodeVisitor, 'depart_custom_node')
+
+
+def test_SphinxFileOutput(tmpdir):
+    content = 'Hello Sphinx World'
+
+    # write test.txt at first
+    filename = str(tmpdir / 'test.txt')
+    output = SphinxFileOutput(destination_path=filename)
+    output.write(content)
+    os.utime(filename, (0, 0))
+
+    # overrite it again
+    output.write(content)
+    assert os.stat(filename).st_mtime != 0  # updated
+
+    # write test2.txt at first
+    filename = str(tmpdir / 'test2.txt')
+    output = SphinxFileOutput(destination_path=filename, overwrite_if_changed=True)
+    output.write(content)
+    os.utime(filename, (0, 0))
+
+    # overrite it again
+    output.write(content)
+    assert os.stat(filename).st_mtime == 0  # not updated
+
+    # overrite it again (content changed)
+    output.write(content + "; content change")
+    assert os.stat(filename).st_mtime != 0  # updated