Replace place holders when publishing to readthedocs

.readthedocs.yaml

@@ -9,6 +9,9 @@ build:
   os: ubuntu-20.04
   tools:
     python: "3.9"
+  jobs:
+    pre_build:
+      - bash docs/prebuild.sh
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx:

docs/prebuild.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+#
+# Replace place holders for http_archive attrs for rules_haskell with actual values
+#
+
+function die() {
+    echo "error: $*"
+    exit 1
+} >&2
+
+set -euo pipefail || die "cannot set options"
+
+function get_sha256() {
+    curl -L "$1" | python -uc 'import hashlib, sys; print(hashlib.sha256(sys.stdin.buffer.read()).hexdigest())'
+}
+
+if [[ "${READTHEDOCS_VERSION_TYPE}" == branch && "${READTHEDOCS_VERSION_NAME}" == master ]]; then
+    # a commit was pushed to the master branch
+    url="https://github.com/tweag/rules_haskell/archive/${READTHEDOCS_GIT_COMMIT_HASH}.tar.gz"
+    hash=$( get_sha256 "$url" )
+    sed -i \
+        -e '/name = "rules_haskell"/,/url = "/{' \
+        -e '  s%x\{64\}%'"${hash}"'%; ' \
+        -e '  s%/releases/download/vM[.]NN/rules_haskell-%/archive/%' \
+        -e '  s%M[.]NN%'"${READTHEDOCS_GIT_COMMIT_HASH}"'%g ' \
+        -e '}' \
+        docs/haskell-use-cases.rst
+elif [[ "${READTHEDOCS_VERSION_TYPE}" == tag && "${READTHEDOCS_GIT_IDENTIFIER}" == v[0-9]* ]]; then
+    # a version tag was pushed
+    version="${READTHEDOCS_GIT_IDENTIFIER#v}"
+    url="https://github.com/tweag/rules_haskell/releases/download/v${version}/rules_haskell-${version}.tar.gz"
+    hash=$( get_sha256 "$url" )
+
+    sed -i \
+        -e '/name = "rules_haskell"/,/url = "/{' \
+        -e '  s%x\{64\}%'"${hash}"'%; ' \
+        -e '  s%M[.]NN%'"${version}"'%g ' \
+        -e '}' \
+        docs/haskell-use-cases.rst
+else
+    die "cannot handle version type ${READTHEDOCS_VERSION_TYPE} / ${READTHEDOCS_VERSION_NAME}"
+fi