Fix whitespace formatting in CLI help. (#917)

traitlets/config/configurable.py

@@ -300,7 +300,7 @@ def class_get_trait_help(
         if helptext is None:
             helptext = trait.help
         if helptext != "":
-            helptext = "\n".join(wrap_paragraphs(helptext, 76))
+            helptext = "\n\n".join(wrap_paragraphs(helptext, 76))
             lines.append(indent(helptext))
 
         if "Enum" in trait.__class__.__name__:

traitlets/utils/text.py

@@ -5,7 +5,6 @@
 
 import re
 import textwrap
-from textwrap import dedent
 from textwrap import indent as _indent
 from typing import List
 
@@ -14,6 +13,25 @@ def indent(val: str) -> str:
     return _indent(val, "    ")
 
 
+def _dedent(text: str) -> str:
+    """Equivalent of textwrap.dedent that ignores unindented first line."""
+
+    if text.startswith("\n"):
+        # text starts with blank line, don't ignore the first line
+        return textwrap.dedent(text)
+
+    # split first line
+    splits = text.split("\n", 1)
+    if len(splits) == 1:
+        # only one line
+        return textwrap.dedent(text)
+
+    first, rest = splits
+    # dedent everything but the first line
+    rest = textwrap.dedent(rest)
+    return "\n".join([first, rest])
+
+
 def wrap_paragraphs(text: str, ncols: int = 80) -> List[str]:
     """Wrap multiple paragraphs to fit a specified width.
 
@@ -26,7 +44,7 @@ def wrap_paragraphs(text: str, ncols: int = 80) -> List[str]:
     list of complete paragraphs, wrapped to fill `ncols` columns.
     """
     paragraph_re = re.compile(r"\n(\s*\n)+", re.MULTILINE)
-    text = dedent(text).strip()
+    text = _dedent(text).strip()
     paragraphs = paragraph_re.split(text)[::2]  # every other entry is space
     out_ps = []
     indent_re = re.compile(r"\n\s+", re.MULTILINE)