Add checklinks tox env and shell script. (#955)

Also clean up dead links.

11 files changed, 51 insertions, 11 deletions

diff --git a/.travis.yml b/.travis.yml
index 28b8a5d..6eec973 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,6 +21,8 @@ matrix:
           - aspell
           - aspell-en
     - env: TOXENV=pep517check
+    - env: TOXENV=checklinks
+      before_install: npm install -g markdown-link-check
 
 addons:
   apt:
diff --git a/checklinks.sh b/checklinks.sh
new file mode 100755
index 0000000..dd9262b
--- /dev/null
+++ b/checklinks.sh
@@ -0,0 +1,31 @@
+#!/bin/bash
+
+echo "Checking links in documentation..."
+
+# List of files in docs dir
+docs=$(find . -path './docs/*.md')
+# List of files in project root (README, etc)
+extras=$(find . -maxdepth 1 -name '*.md')
+# Combined list of files to check
+files=("${docs[@]}" "${extras[@]}")
+
+let "fails=0"
+let "count=0"
+
+for file in ${files[@]}; do
+    let "count++"
+    markdown-link-check -q "$file"
+    if [ $? -ne 0 ]; then
+        let "fails++"
+    fi
+done
+
+echo -e "\n\033[0;33m$count files checked."
+
+if [ $fails -gt 0 ]; then
+    echo -e "\033[0;31mERROR: $fails files with dead links found!"
+    exit 1
+else
+    echo -e "\033[0;32mCongratulations! No dead links found."
+    exit 0
+fi
diff --git a/docs/authors.md b/docs/authors.md
index ba674c3..6b164fd 100644
--- a/docs/authors.md
+++ b/docs/authors.md
@@ -28,7 +28,7 @@ Primary Authors
     Ph.D. Various pieces of his code still exist, most notably the basic
     structure.
 
-* __[Manfed Stienstra](http://www.dwerg.net/)__
+* __Manfed Stienstra__
 
     Manfed wrote the original version of the script and is responsible for
     various parts of the existing code base.
diff --git a/docs/change_log/index.md b/docs/change_log/index.md
index c070295..8975de6 100644
--- a/docs/change_log/index.md
+++ b/docs/change_log/index.md
@@ -5,6 +5,7 @@ Python-Markdown Change Log
 
 Under development: version 3.2.2 (a bug-fix release).
 
+* Add `checklinks` tox environment to ensure all links in documentation are good.
 * Refactor extension API documentation (#729).
 * Load entry_points (for extensions) only once using `importlib.metadata`.
 * Do not double escape entities in TOC.
@@ -262,4 +263,4 @@ escape, emphasis in the beginning of the paragraph.
 Nov. 2004: Added links, blockquotes, HTML blocks to Manfred
 Stienstra's code
 
-Apr. 2004: Manfred's version at <http://www.dwerg.net/projects/markdown/>
+Apr. 2004: Manfred's version at `http://www.dwerg.net/projects/markdown/`
diff --git a/docs/change_log/release-2.2.md b/docs/change_log/release-2.2.md
index 379a43e..75f47fa 100644
--- a/docs/change_log/release-2.2.md
+++ b/docs/change_log/release-2.2.md
@@ -40,7 +40,7 @@ What's New in Python-Markdown 2.2
 ---------------------------------
 
 The docs were refactored and can now be found at
-<http://packages.python.org/Markdown/>. The docs are now maintained in the
+`http://packages.python.org/Markdown/`. The docs are now maintained in the
 Repository and are generated by the `setup.py build_docs` command.
 
 The [Sane_Lists](../extensions/sane_lists.md)
diff --git a/docs/change_log/release-2.3.md b/docs/change_log/release-2.3.md
index fc1809e..f60e426 100644
--- a/docs/change_log/release-2.3.md
+++ b/docs/change_log/release-2.3.md
@@ -58,7 +58,7 @@ Backwards-incompatible Changes
   PyTidyLib rather than using an extension (for example:
   `tidylib.tidy_fragment(markdown.markdown(source), options={...})`).
 
-[PyTidyLib]: http://countergram.com/open-source/pytidylib
+[PyTidyLib]: http://countergram.github.io/pytidylib/
 
 What's New in Python-Markdown 2.3
 ---------------------------------
diff --git a/docs/contributing.md b/docs/contributing.md
index ca95042..974d380 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -9,7 +9,7 @@ propose changes to this document in a pull request.
 
 This project and everyone participating in it is governed by the
 [Python-Markdown Code of Conduct]. By participating, you are expected to uphold
-this code. Please report unacceptable behavior to <markdown@freewisdom.org>.
+this code. Please report unacceptable behavior to [markdown@freewisdom.org][email].
 
 ## Project Organization
 
@@ -473,6 +473,7 @@ label from the same group.
 
 [Python-Markdown Organization]: https://github.com/Python-Markdown
 [Python-Markdown Code of Conduct]: https://github.com/Python-Markdown/markdown/blob/master/CODE_OF_CONDUCT.md
+[email]: mailto:markdown@freewisdom.org
 [Python-Markdown/markdown]: https://github.com/Python-Markdown/markdown
 [issue tracker]: https://github.com/Python-Markdown/markdown/issues
 [syntax rules]: https://daringfireball.net/projects/markdown/syntax
@@ -495,7 +496,7 @@ label from the same group.
 [configure a remote]: https://help.github.com/articles/configuring-a-remote-for-a-fork
 [sync changes]: https://help.github.com/articles/syncing-a-fork
 [virtual environment]: https://virtualenv.pypa.io/en/stable/
-[User Guide]: https://virtualenv.pypa.io/en/stable/userguide/#usage
+[User Guide]: https://virtualenv.pypa.io/en/stable/user_guide.html
 [Development Mode]: https://setuptools.readthedocs.io/en/latest/setuptools.html#development-mode
 [PyTidyLib]: https://countergram.github.io/pytidylib/
 [HTML Tidy]: https://www.html-tidy.org/
diff --git a/docs/extensions/admonition.md b/docs/extensions/admonition.md
index 886320a..24d8254 100644
--- a/docs/extensions/admonition.md
+++ b/docs/extensions/admonition.md
@@ -99,7 +99,7 @@ Styling
 There is no CSS included as part of this extension. Check out the default
 [Sphinx][sphinx] theme for inspiration.
 
-[sphinx]: http://sphinx.pocoo.org/
+[sphinx]: https://www.sphinx-doc.org/en/stable/
 
 ## Usage
 
diff --git a/docs/extensions/attr_list.md b/docs/extensions/attr_list.md
index d89eac2..4dcbc59 100644
--- a/docs/extensions/attr_list.md
+++ b/docs/extensions/attr_list.md
@@ -11,9 +11,9 @@ This extension is included in the standard Markdown library.
 
 ## Syntax
 
-The basic syntax was inspired by [Maruku][]'s Attribute Lists feature.
+The basic syntax was inspired by Maruku's Attribute Lists feature (see [web archive][Maruku]).
 
-[Maruku]: http://maruku.rubyforge.org/proposal.html#attribute_lists
+[Maruku]: https://web.archive.org/web/20170324172643/http://maruku.rubyforge.org/proposal.html
 
 ### The List
 
diff --git a/docs/test_tools.md b/docs/test_tools.md
index c252086..3a83d8e 100644
--- a/docs/test_tools.md
+++ b/docs/test_tools.md
@@ -169,6 +169,6 @@ rules apply.
 [unittest]: https://docs.python.org/3/library/unittest.html
 [Perl]: https://daringfireball.net/projects/markdown/
 [PHP]: http://michelf.com/projects/php-markdown/
-[PyTidyLib]: http://countergram.com/open-source/pytidylib/
+[PyTidyLib]: http://countergram.github.io/pytidylib/
 [Contributing Guide]: contributing.md
 [development environment]: contributing.md#development-environment
diff --git a/tox.ini b/tox.ini
index 14dcc21..ea153e4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py35, py36, py37, py38, pypy3, flake8, checkspelling, pep517check
+envlist = py35, py36, py37, py38, pypy3, flake8, checkspelling, pep517check, checklinks
 isolated_build = True
 min_verison = 1.9
 
@@ -20,6 +20,11 @@ deps =
     mkdocs_nature
 commands = {toxinidir}/checkspelling.sh
 
+[testenv:checklinks]
+whitelist_externals = markdown-link-check
+deps =
+commands = {toxinidir}/checklinks.sh
+
 [testenv:pep517check]
 deps = pep517
 commands = python -m pep517.check {toxinidir}