version: calculate version info without using git tags.

This makes it easier to integrate this version math into a submodule-ful
world. We'll continue to have regular git tags that parallel the information
in VERSION, so that builds out of this repository behave the same.

Signed-off-by: David Anderson <danderson@tailscale.com>

VERSION

@@ -0,0 +1 @@
+1.1.0 f81233524fddeec450940af8dc1a0dd8841bf28c

build_dist.sh

@@ -11,10 +11,8 @@
 
 set -euo pipefail
 
-describe=$(git describe --long --abbrev=9)
-# --abbrev=200 is an arbitrary large number to capture the entire git
-# hash without trying to compact it.
-commit=$(git describe --dirty --exclude "*" --always --abbrev=200)
+describe=$(./version/describe.sh)
+commit=$(git rev-parse --verify --quiet HEAD)
 
 long=$(./version/mkversion.sh long "$describe" "")
 short=$(./version/mkversion.sh short "$describe" "")

version/describe.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+#
+# Constructs a "git describe" compatible version number by using the
+# information in the VERSION file, rather than git tags.
+
+set -eu
+
+dir="$(dirname $0)"
+verfile="$dir/../VERSION"
+
+read -r version hash <"$verfile"
+
+if [ -z "$hash" ]; then
+    # If no explicit hash was given, use the last time the version
+    # file changed as the "origin" hash for this version.
+    hash="$(git rev-list --max-count=1 HEAD -- $verfile)"
+fi
+
+if [ -z "$hash" ]; then
+    echo "Couldn't find base git hash for version '$version'" >2
+    exit 1
+fi
+
+head="$(git rev-parse --short=9 HEAD)"
+changecount="$(git rev-list ${hash}..HEAD | wc -l)"
+echo "v${version}-${changecount}-g${head}"

version/describe.txt.do

@@ -1,4 +1,3 @@
-describe=$(git describe --long --abbrev=9)
-echo "$describe" >$3
+./describe.sh >$3
 redo-always
 redo-stamp <$3