Use single file upgrades where possible.

extensions/ql-vscode/src/pure/messages.ts

@@ -406,6 +406,11 @@ export interface CompileUpgradeParams {
    * A directory to store parts of the compiled upgrade
    */
   upgradeTempDir: string;
+  /** 
+   * Enable single file upgrades, set to true to allow
+   * using single file upgrades.
+   */
+  singleFileUpgrades?: boolean;
 }
 
 /**
@@ -492,10 +497,42 @@ export interface UpgradeDescription {
   newSha: string;
 }
 
+
+export type CompiledUpgrades = MultiFileCompiledUpgrades | SingleFileCompiledUpgrade
+
 /**
  * A compiled upgrade. 
+ * The upgrade is spread among multiple files.
  */
-export interface CompiledUpgrades {
+export interface MultiFileCompiledUpgrades {
+  /**
+  * The initial sha of the dbscheme to upgrade from
+  */
+  initialSha: string;
+  /**
+   * The path to the new dataset statistics
+   */
+  newStatsPath: string;
+  /**
+   * The path to the new dataset dbscheme
+   */
+  newDbscheme: string;
+  /**
+   * The steps in the upgrade path
+   */
+  scripts: CompiledUpgradeScript[];
+  /**
+   * Will never exist in an old result
+   */
+  compiledUpgradeFile?: never;
+  /**
+   * The sha of the target dataset.
+   */
+  targetSha: string;
+}
+
+
+export interface SingleFileCompiledUpgrade {
   /**
   * The initial sha of the dbscheme to upgrade from
   */
@@ -507,7 +544,11 @@ export interface CompiledUpgrades {
   /**
    * The steps in the upgrade path
    */
-  scripts: CompiledUpgradeScript[];
+  descriptions: UpgradeDescription[];
+  /**
+   * The file containing the upgrade
+   */
+  compiledUpgradeFile: string;
   /**
    * The sha of the target dataset.
    */

extensions/ql-vscode/src/upgrades.ts

@@ -157,7 +157,11 @@ export async function upgradeDatabase(
 
   try {
     qs.logger.log('Running the following database upgrade:');
-    qs.logger.log(compileUpgradeResult.compiledUpgrades.scripts.map(s => s.description.description).join('\n'));
+    if (compileUpgradeResult.compiledUpgrades.compiledUpgradeFile === undefined) {
+      qs.logger.log(compileUpgradeResult.compiledUpgrades.scripts.map(s => s.description.description).join('\n'));
+    } else {
+      qs.logger.log(compileUpgradeResult.compiledUpgrades.descriptions.map(s => s.description).join('\n'));
+    }
     return await runDatabaseUpgrade(qs, db, compileUpgradeResult.compiledUpgrades, progress, token);
   }
   catch (e) {
@@ -192,7 +196,8 @@ async function compileDatabaseUpgrade(
 ): Promise<messages.CompileUpgradeResult> {
   const params: messages.CompileUpgradeParams = {
     upgrade: upgradeParams,
-    upgradeTempDir: upgradesTmpDir.name
+    upgradeTempDir: upgradesTmpDir.name,
+    singleFileUpgrades: true
   };
 
   progress({