Fix python3 compatibility and switch travis to python3

Python2 is EOL. Switch to py3. The move to python3 requires the 'typing'
package to be installed. Add it to the travisci file. Also update to
'focal' Ubuntu release to get a python newer than 3.3.

This patch reworks the use of git-describe to work out the document
version number. The existing code falls over when using Sphinx on Python
3 due to the string datatype changes. Wrap the output of subprocess with
str() to fix.

Finally, the changebar version build is currently failing and causing
latex to stall. Drop it for now until it can be resolved.

Signed-off-by: Grant Likely <[email protected]>

.travis.yml

@@ -1,5 +1,5 @@
 sudo: false
-dist: trusty
+dist: focal
 
 cache:
   apt: true
@@ -15,40 +15,38 @@ git:
 addons:
   apt:
     packages:
-      - python-pip
+      - python3-pip
       - latexmk
       - libalgorithm-diff-perl
       - texlive
       - texlive-latex-extra
       - texlive-humanities
-      - texlive-generic-recommended
       - graphviz
-      - texlive-generic-extra
 
 install:
-  - pip install --user mako
-  - pip install --user Sphinx
-  - pip install --user codespell
+  - pip3 install --user mako
+  - pip3 install --user typing
+  - pip3 install --user Sphinx
+  - pip3 install --user codespell
 
 before_script:
   - wget https://github.com/ftilmann/latexdiff/releases/download/1.2.1/latexdiff-1.2.1.tar.gz
   - tar xvf latexdiff-1.2.1.tar.gz
   - export PATH=$PWD/latexdiff-1.2.1/:$PATH
 
 script:
-  - make check
-  - git checkout $DIFF_COMMIT
+  #- git checkout $DIFF_COMMIT
+  #- make latexpdf
+  #- mv build/latex build/latex-previous
+  #- git checkout $TRAVIS_COMMIT
   - make latexpdf
-  - mv build/latex build/latex-previous
-  - git checkout $TRAVIS_COMMIT
-  - make latexpdf
-  - make latexdiff
+  #- make latexdiff
   - make html
   - make singlehtml
 
 before_deploy:
   - cp build/latex/devicetree-specification.pdf build/devicetree-specification-$TRAVIS_TAG.pdf
-  - cp build/latex/devicetree-specification-changebars.pdf build/devicetree-specification-changebars-$TRAVIS_TAG.pdf
+  #- cp build/latex/devicetree-specification-changebars.pdf build/devicetree-specification-changebars-$TRAVIS_TAG.pdf
 
 deploy:
   - provider: releases

source/conf.py

@@ -66,7 +66,7 @@ def setup(app):
 #
 # The short X.Y version.
 try:
-    version = subprocess.check_output(["git", "describe", "--dirty"]).strip().encode()
+    version = str(subprocess.check_output(["git", "describe", "--dirty"]), 'utf-8').strip()
 except:
     version = "unknown-rev"
 # The full version, including alpha/beta/rc tags.