fix: raise the android versionCode with every release

`versionCode` was hard-coded to 1, so every release looked like the
same version to Android. It is now derived from `VERSION` as
`major * 10000000 + minor * 10000 + patch` (0.1.62 gives 10062), which
is above the 1 existing installs have and keeps growing, so Android
never mistakes an update for a downgrade.

The formula only increases while patch stays below 10000 and minor
below 1000. `build.gradle` refuses a `VERSION` outside that range or
outside Android's 2100000000 ceiling, and `scripts/bump-version.mjs`,
which only ever bumps patch, refuses to create such a version before
anything is committed or tagged.

android/app/build.gradle

@@ -7,6 +7,31 @@ def projectRoot = rootDir.getAbsoluteFile().getParentFile().getAbsolutePath()
 
 def appVersionName = file("${projectRoot}/VERSION").text.trim()
 
+/**
+ * versionCode has to grow with every release, or Android refuses the update as
+ * a downgrade. It is derived from VERSION as
+ *
+ *     major * 10000000 + minor * 10000 + patch      (0.1.62 -> 10062)
+ *
+ * which keeps increasing as long as patch stays below 10000 and minor below
+ * 1000 (scripts/bump-version.mjs, which only ever bumps patch, enforces both),
+ * and stays under Android's 2100000000 ceiling up to major 209.
+ */
+def versionParts = (appVersionName =~ /^(\d+)\.(\d+)\.(\d+)$/)
+if (!versionParts.matches()) {
+    throw new GradleException("VERSION must be MAJOR.MINOR.PATCH, got '${appVersionName}'")
+}
+def (versionMajor, versionMinor, versionPatch) = (1..3).collect { versionParts.group(it) as long }
+if (versionMinor > 999 || versionPatch > 9999) {
+    throw new GradleException("VERSION ${appVersionName}: minor must stay below 1000 and patch below 10000, " +
+            "or versionCode stops increasing. Move to the next minor or major version instead.")
+}
+def appVersionCode = versionMajor * 10000000L + versionMinor * 10000L + versionPatch
+if (appVersionCode < 1 || appVersionCode > 2100000000L) {
+    throw new GradleException("VERSION ${appVersionName} gives versionCode ${appVersionCode}, " +
+            "outside the 1..2100000000 range Android accepts.")
+}
+
 /**
  * Release signing. The key never lives in the repo: CI passes it as
  * ORG_GRADLE_PROJECT_BULWARK_RELEASE_* environment variables, and a local
@@ -126,7 +151,7 @@ android {
         applicationId 'com.anonymous.bulwarkmobile'
         minSdkVersion rootProject.ext.minSdkVersion
         targetSdkVersion rootProject.ext.targetSdkVersion
-        versionCode 1
+        versionCode appVersionCode.toInteger()
         versionName appVersionName
 
         buildConfigField "String", "REACT_NATIVE_RELEASE_LEVEL", "\"${findProperty('reactNativeReleaseLevel') ?: 'stable'}\""

scripts/bump-version.mjs

@@ -42,6 +42,15 @@ if (parts.length !== 3 || parts.some(Number.isNaN)) {
 parts[2] += 1;
 const next = parts.join('.');
 
+// android/app/build.gradle derives versionCode as
+// major * 10000000 + minor * 10000 + patch. Past these limits it would stop
+// increasing, and Android refuses an update with a lower versionCode.
+if (parts[1] > 999 || parts[2] > 9999) {
+  console.error(`${next} would break the Android versionCode: minor must stay below 1000 and patch below 10000.`);
+  console.error('Raise the minor or major version in VERSION by hand and commit it, then bump again.');
+  process.exit(1);
+}
+
 const existingTags = new Set(git('tag', '--list').split(/\r?\n/).filter(Boolean));
 if (existingTags.has(next)) {
   console.error(`Tag ${next} already exists.`);