fix Publisher Workflow to successfully create new branches (#3117)

The publisher tool was unable to create new branches because it
attempted to determine if the current commit was on main. However, this
didn't work! Since main was never checked out (ever) in the repo, there
was no ref to look for. This fixes the issue in (perhaps not the best)
way by simply checking out main first.

The logic was also refactored to have dry run and non-dry run behave in
a way that is closer to identical.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

.github/scripts/get-or-create-release-branch.sh

@@ -14,15 +14,15 @@ set -eux
 # is the beginning of a new release series.
 
 if [ -z "$SEMANTIC_VERSION" ]; then
-    echo "'SEMANTIC_VERSION' must be populated."
-    exit 1
+  echo "'SEMANTIC_VERSION' must be populated."
+  exit 1
 fi
 
 if [ -z "$1" ]; then
-    echo "You need to specify the path of the file where you want to collect the output"
-    exit 1
+  echo "You need to specify the path of the file where you want to collect the output"
+  exit 1
 else
-    output_file="$1"
+  output_file="$1"
 fi
 
 # Split on the dots
@@ -31,41 +31,50 @@ major=${version_array[0]}
 minor=${version_array[1]}
 patch=${version_array[2]}
 if [[ "${major}" == "" || "${minor}" == "" || "${patch}" == "" ]]; then
-    echo "'${SEMANTIC_VERSION}' is not a valid semver tag"
-    exit 1
+  echo "'${SEMANTIC_VERSION}' is not a valid semver tag"
+  exit 1
 fi
 if [[ $major == 0 ]]; then
-    branch_name="smithy-rs-release-${major}.${minor}.x"
-    if [[ $patch == 0 ]]; then
-        echo "new_release_series=true" >"${output_file}"
-    fi
+  branch_name="smithy-rs-release-${major}.${minor}.x"
+  if [[ $patch == 0 ]]; then
+    echo "new_release_series=true" >"${output_file}"
+  fi
 else
-    branch_name="smithy-rs-release-${major}.x.y"
-    if [[ $minor == 0 && $patch == 0 ]]; then
-        echo "new_release_series=true" >"${output_file}"
-    fi
+  branch_name="smithy-rs-release-${major}.x.y"
+  if [[ $minor == 0 && $patch == 0 ]]; then
+    echo "new_release_series=true" >"${output_file}"
+  fi
 fi
 
 if [[ "${DRY_RUN}" == "true" ]]; then
-    branch_name="${branch_name}-preview"
+  branch_name="${branch_name}-preview"
 fi
 echo "release_branch=${branch_name}" >"${output_file}"
 
-if [[ "${DRY_RUN}" == "true" ]]; then
-    git push --force origin "HEAD:refs/heads/${branch_name}"
-else
-    commit_sha=$(git rev-parse --short HEAD)
-    if ! git ls-remote --exit-code --heads origin "${branch_name}"; then
-        # The release branch does not exist.
-        # We need to make sure that the commit SHA that we are releasing is on `main`.
-        git fetch origin main
-        if git branch --contains "${commit_sha}" | grep main; then
-            # We can then create the release branch and set the current commit as its tip
-            git checkout -b "${branch_name}"
-            git push origin "${branch_name}"
-        else
-            echo "You must choose a commit from main to create a new release branch!"
-            exit 1
-        fi
+commit_sha=$(git rev-parse --short HEAD)
+# the git repo is in a weird state because **main has never been checked out**!
+# This prevents the `git branch --contains` from working because there is no _local_ ref for main
+git checkout main
+git checkout "${commit_sha}"
+if ! git ls-remote --exit-code --heads origin "${branch_name}"; then
+  # The release branch does not exist.
+  # We need to make sure that the commit SHA that we are releasing is on `main`.
+  git fetch origin main
+  echo "Branches: "
+  git branch --contains "${commit_sha}"
+  git show origin/main | head -n 1
+  if git branch --contains "${commit_sha}" | grep main; then
+    # We can then create the release branch and set the current commit as its tip
+    if [[ "${DRY_RUN}" == "true" ]]; then
+      git push --force origin "HEAD:refs/heads/${branch_name}"
+    else
+      git checkout -b "${branch_name}"
+      git push origin "${branch_name}"
     fi
+  else
+    echo "You must choose a commit from main to create a new release branch!"
+    exit 1
+  fi
+else
+  echo "Patch release ${branch_name} already exists"
 fi