krb5 commit: Add doc build to Github Actions config

https://github.com/krb5/krb5/commit/414d67b321e79b2f33d578a1e7fdf7dee726cdde
commit 414d67b321e79b2f33d578a1e7fdf7dee726cdde
Author: Greg Hudson <[email protected]>
Date:   Sun Sep 20 16:41:08 2020 -0400

    Add doc build to Github Actions config
    
    Add a second workflow to build documentation, with the HTML output as
    a generated artifact.  Skip the doc workflow if no documentation files
    were changed.  Skip the existing build workflow if no source files
    were changed.

 .github/workflows/build.yml |    4 +++-
 .github/workflows/doc.yml   |   27 +++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 2af7da2..8d1042b 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -1,6 +1,8 @@
 name: Build
 
-on: [push, pull_request]
+on:
+    push: {paths: [src/**, .github/workflows/build.yml]}
+    pull_request: {paths: [src/**, .github/workflows/build.yml]}
 
 jobs:
 
diff --git a/.github/workflows/doc.yml b/.github/workflows/doc.yml
new file mode 100644
index 0000000..292df4c
--- /dev/null
+++ b/.github/workflows/doc.yml
@@ -0,0 +1,27 @@
+name: Doc
+
+on:
+    push: {paths: [doc/**, src/doc/*, src/include/krb5/krb5.hin, .github/workflows/doc.yml]}
+    pull_request: {paths: [doc/**, src/doc/*, src/include/krb5/krb5.hin, .github/workflows/doc.yml]}
+
+jobs:
+    doc:
+        runs-on: ubuntu-18.04
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@v1
+            - name: Linux setup
+              run: |
+                sudo apt-get update -qq
+                sudo apt-get install -y doxygen python3-lxml python3-pip python-sphinx
+                pip3 install Cheetah3
+            - name: Build documentation
+              run: |
+                cd src/doc
+                make -f Makefile.in SPHINX_ARGS=-W htmlsrc
+            - name: Upload HTML
+              uses: actions/upload-artifact@v2
+              with:
+                  name: html
+                  path: doc/html
+                  retention-days: 7