Require a space after hash marks for ATX headers

This was required by the original ATX specification, although
Markdown.pl didn't enforce it.  It prevents false positives for
#hashtags and things like "Engine #1" when lines wrap.  It also
reinforces good style.

Author: jrblevin

markdown-mode.el

@@ -1215,7 +1215,7 @@ Group 2 matches only the label, without the surrounding markup.
 Group 3 matches the closing square bracket.")
 
 (defconst markdown-regex-header
-  "^\\(?:\\(.+?\\)\n\\(?:\\(=+\\)\\|\\(-+\\)\\)\\|\\(#+\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)\\)$"
+  "^\\(?:\\(.+?\\)\n\\(?:\\(=+\\)\\|\\(-+\\)\\)\\|\\(#+\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)\\)$"
   "Regexp identifying Markdown headings.
 Group 1 matches the text of a setext heading.
 Group 2 matches the underline of a level-1 setext heading.
@@ -1225,27 +1225,27 @@ Group 5 matches the text, without surrounding whitespace, of an atx heading.
 Group 6 matches the closing hash marks of an atx heading.")
 
 (defconst markdown-regex-header-1-atx
-  "^\\(#\\)[ \t]*\\([^\\.].*?\\)[ \t]*\\(#*\\)$"
+  "^\\(#\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 1 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-2-atx
-  "^\\(##\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)$"
+  "^\\(##\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 2 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-3-atx
-  "^\\(###\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)$"
+  "^\\(###\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 3 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-4-atx
-  "^\\(####\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)$"
+  "^\\(####\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 4 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-5-atx
-  "^\\(#####\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)$"
+  "^\\(#####\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 5 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-6-atx
-  "^\\(######\\)[ \t]*\\(.+?\\)[ \t]*\\(#*\\)$"
+  "^\\(######\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for level 6 atx-style (hash mark) headers.")
 
 (defconst markdown-regex-header-1-setext
@@ -1261,7 +1261,7 @@ Group 6 matches the closing hash marks of an atx heading.")
   "Regular expression for generic setext-style (underline) headers.")
 
 (defconst markdown-regex-header-atx
-  "^\\(#+\\)[ \t]*\\(.*?\\)[ \t]*\\(#*\\)$"
+  "^\\(#+\\)[ \t]+\\(.*?\\)[ \t]*\\(#*\\)$"
   "Regular expression for generic atx-style (hash mark) headers.")
 
 (defconst markdown-regex-hr

tests/markdown-test.el

@@ -1430,8 +1430,7 @@ the opening bracket of [^2], and then subsequent functions would kill [^2])."
                         (should (looking-at markdown-regex-header-atx))
                         (should-not (markdown-incomplete-atx-p)))
   (markdown-test-string "###abc###"
-                        (should (looking-at markdown-regex-header-atx))
-                        (should (markdown-incomplete-atx-p)))
+                        (should-not (looking-at markdown-regex-header-atx)))
   (markdown-test-string "###   ###"
                         (should (looking-at markdown-regex-header-atx))
                         (should (markdown-incomplete-atx-p))))
@@ -2205,15 +2204,11 @@ for (var i = 0; i < 10; i++) {
 (ert-deftest test-markdown-font-lock/atx-no-spaces ()
   "Test font-lock for atx headers with no spaces."
   (markdown-test-string "##abc##"
-   (markdown-test-range-has-face 1 2 markdown-header-delimiter-face)
-   (markdown-test-range-has-face 3 5 markdown-header-face-2)
-   (markdown-test-range-has-face 6 7 markdown-header-delimiter-face))
+   (markdown-test-range-has-face 1 7 nil))
   (markdown-test-string "##"
-   (markdown-test-range-has-face 1 1 markdown-header-delimiter-face)
-   (markdown-test-range-has-face 2 2 markdown-header-face-1))
+   (markdown-test-range-has-face 1 2 nil))
   (markdown-test-string "###"
-   (markdown-test-range-has-face 1 2 markdown-header-delimiter-face)
-   (markdown-test-range-has-face 3 3 markdown-header-face-2)))
+   (markdown-test-range-has-face 1 3 nil)))
 
 (ert-deftest test-markdown-font-lock/setext-1-letter ()
   "An edge case for level-one setext headers."