Split `format_traceback() from save_traceback()`

sphinx/_cli/util/errors.py

@@ -51,6 +51,7 @@ def strip_escape_sequences(text: str, /) -> str:
 
 
 def error_info(messages: str, extensions: str, traceback: str) -> str:
+    """Format the traceback and extensions list with environment information."""
     import platform
 
     import docutils
@@ -87,8 +88,8 @@ Traceback
 """
 
 
-def save_traceback(app: Sphinx | None, exc: BaseException) -> str:
-    """Save the given exception's traceback in a temporary file."""
+def format_traceback(app: Sphinx | None, exc: BaseException) -> str:
+    """Format the given exception's traceback with environment information."""
     if isinstance(exc, SphinxParallelError):
         exc_format = '(Error in parallel process)\n' + exc.traceback
     else:
@@ -106,6 +107,12 @@ def save_traceback(app: Sphinx | None, exc: BaseException) -> str:
             if ext.version != 'builtin'
         )
 
+    return error_info(last_msgs, exts_list, exc_format)
+
+
+def save_traceback(app: Sphinx | None, exc: BaseException) -> str:
+    """Save the given exception's traceback in a temporary file."""
+    output = format_traceback(app=app, exc=exc)
     with tempfile.NamedTemporaryFile(
         suffix='.log', prefix='sphinx-err-', delete=False
     ) as f:

sphinx/util/exceptions.py

@@ -5,8 +5,7 @@ import traceback
 from tempfile import NamedTemporaryFile
 from typing import TYPE_CHECKING
 
-from sphinx.errors import SphinxParallelError
-from sphinx.util.console import strip_escape_sequences
+from sphinx._cli.util.errors import format_traceback
 
 if TYPE_CHECKING:
     from sphinx.application import Sphinx
@@ -14,52 +13,10 @@ if TYPE_CHECKING:
 
 def save_traceback(app: Sphinx | None, exc: BaseException) -> str:
     """Save the given exception's traceback in a temporary file."""
-    import platform
-
-    import docutils
-    import jinja2
-    import pygments
-
-    import sphinx
-
-    if isinstance(exc, SphinxParallelError):
-        exc_format = '(Error in parallel process)\n' + exc.traceback
-    else:
-        exc_format = traceback.format_exc()
-
-    if app is None:
-        last_msgs = exts_list = ''
-    else:
-        extensions = app.extensions.values()
-        last_msgs = '\n'.join(
-            f'#   {strip_escape_sequences(s).strip()}' for s in app.messagelog
-        )
-        exts_list = '\n'.join(
-            f'#   {ext.name} ({ext.version})'
-            for ext in extensions
-            if ext.version != 'builtin'
-        )
-
     with NamedTemporaryFile(
         'w', encoding='utf-8', suffix='.log', prefix='sphinx-err-', delete=False
     ) as f:
-        f.write(f"""\
-# Platform:         {sys.platform}; ({platform.platform()})
-# Sphinx version:   {sphinx.__display_version__}
-# Python version:   {platform.python_version()} ({platform.python_implementation()})
-# Docutils version: {docutils.__version__}
-# Jinja2 version:   {jinja2.__version__}
-# Pygments version: {pygments.__version__}
-
-# Last messages:
-{last_msgs}
-
-# Loaded extensions:
-{exts_list}
-
-# Traceback:
-{exc_format}
-""")
+        f.write(format_traceback(app, exc))
     return f.name