version.sh: remove use of `git describe --exclude`

This option isn't available on slightly older versions of git. We were
no longer using the real describe functionality anyway, so let's just do
something simpler to detect a dirty worktree.

While we're here, fix up a little bit of sh style.

Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>

version/version.sh

@@ -1,22 +1,43 @@
 #!/bin/sh
-
 set -eu
 
+# Return the commitid of the given ref in the given repo dir. If the worktree
+# or index is dirty, also appends -dirty.
+#
+# $ git_hash_dirty ../.. HEAD
+# 1be01ddc6e430ca3aa9beea3587d16750efb3241-dirty
+git_hash_dirty() {
+    (
+        cd "$1" &&
+        x=$(git rev-parse HEAD) &&
+        if ! git diff-index --quiet HEAD; then
+            x="$x-dirty"
+        fi
+        echo "$x"
+    )
+}
+
 case $# in
     0|1)
-        # extra_hash describes a git repository other than the current
-        # one. It gets embedded as an additional commit hash in built
+        # extra_hash_or_dir is either:
+        #   - a git commitid
+        # or
+        #   - the path to a git repo from which to calculate the real hash.
+        #
+        # It gets embedded as an additional commit hash in built
         # binaries, to help us locate the exact set of tools and code
         # that were used.
-        extra_hash="${1:-}"
-        if [ -z "$extra_hash" ]; then
+        extra_hash_or_dir="${1:-}"
+        if [ -z "$extra_hash_or_dir" ]; then
             # Nothing, empty extra hash is fine.
             extra_hash=""
-        elif [ -e "$extra_hash/.git" ]; then
-            extra_hash=$(cd "$extra_hash" && git describe --always --dirty --exclude '*' --abbrev=200)
+        elif [ -d "$extra_hash_or_dir/.git" ]; then
+            extra_hash=$(git_hash_dirty "$extra_hash_or_dir" HEAD)
         elif ! expr "$extra_hash" : "^[0-9a-f]*$"; then
             echo "Invalid extra hash '$extra_hash', must be a git commit hash or path to a git repo" >&2
             exit 1
+        else
+            extra_hash="$extra_hash_or_dir"
         fi
 
         # Load the base version and optional corresponding git hash
@@ -25,15 +46,12 @@ case $# in
         version_file="$(dirname $0)/../VERSION.txt"
         IFS=".$IFS" read -r major minor patch base_git_hash <"$version_file"
         if [ -z "$base_git_hash" ]; then
-            base_git_hash=$(git rev-list --max-count=1 HEAD -- $version_file)
+            base_git_hash=$(git rev-list --max-count=1 HEAD -- "$version_file")
         fi
 
-        # The full git has we're currently building at. --abbrev=200 is an
-        # arbitrary large number larger than all currently-known hashes, so
-        # that git displays the full commit hash.
-        git_hash=$(git describe --always --dirty --exclude '*' --abbrev=200)
+        git_hash=$(git_hash_dirty . HEAD)
         # The number of extra commits between the release base to git_hash.
-        change_count=$(git rev-list ${base_git_hash}..HEAD | wc -l | sed 's/ *//')
+        change_count=$(git rev-list --count HEAD "^$base_git_hash")
         ;;
     6)
         # Test mode: rather than run git commands and whatnot, take in
@@ -52,8 +70,8 @@ esac
 
 # Shortened versions of git hashes, so that they fit neatly into an
 # "elongated" but still human-readable version number.
-short_git_hash=$(echo $git_hash | cut -c-9)
-short_extra_hash=$(echo $extra_hash | cut -c-9)
+short_git_hash=$(echo "$git_hash" | cut -c1-9)
+short_extra_hash=$(echo "$extra_hash" | cut -c1-9)
 
 # Convert major/minor/patch/change_count into an adjusted
 # major/minor/patch. This block is where all our policies on
@@ -62,7 +80,7 @@ if expr "$minor" : "[0-9]*[13579]$" >/dev/null; then
     # Odd minor numbers are unstable builds.
     if [ "$patch" != "0" ]; then
         # This is a fatal error, because a non-zero patch number
-        # indicates that we created an unstable git tag in violation
+        # indicates that we created an unstable VERSION.txt in violation
         # of our versioning policy, and we want to blow up loudly to
         # get that fixed.
         echo "Unstable release $major.$minor.$patch has a non-zero patch number, which is not allowed" >&2
@@ -100,10 +118,10 @@ else
     long_version_suffix="-t${short_git_hash}-g${short_extra_hash}"
 fi
 cat <<EOF
-VERSION_SHORT="${major}.${minor}.${patch}"
-VERSION_LONG="${major}.${minor}.${patch}${long_version_suffix}"
-VERSION_GIT_HASH="${git_hash}"
-VERSION_EXTRA_HASH="${extra_hash}"
-VERSION_XCODE="$((major + 100)).${minor}.${patch}"
-VERSION_WINRES="${major},${minor},${patch},0"
+VERSION_SHORT="$major.$minor.$patch"
+VERSION_LONG="$major.$minor.$patch$long_version_suffix"
+VERSION_GIT_HASH="$git_hash"
+VERSION_EXTRA_HASH="$extra_hash"
+VERSION_XCODE="$((major + 100)).$minor.$patch"
+VERSION_WINRES="$major,$minor,$patch,0"
 EOF