vscode: Ensure extension.js is rebuilt when deleted

Right now, the vscode-extension:continue-ui:build task
deletes extension.js as part of its prepackage.js script.

This wouldn't normally be a problem, because extension.js
is generated by the vscode-extension:esbuild, and
vscode-extension:continue-ui:build is a dependency of
vscode-extension:esbuild, implying it should always get run
first.

But, vscode-extension:esbuild is a background task, that stays
running after it's been started once. Future calls to run that
task become no-ops, because it's already active. This means running

vscode-extension:esbuild ->
  vscode-extension:continue-ui:build ->
    vscode-extension:esbuild

will lead to the last vscode-extension:esbuild not regenerating
extension.js.

In order to resolve that problem, this commit adds a new foreground
task into the build pipeline:

  vscode-extension:esbuild-notify

that tickles the watching background task to wake up and regenerate
extension.js

.vscode/tasks.json

@@ -28,6 +28,9 @@
         "vscode-extension:continue-ui:build",
         // // To bundle the code the same way we do for publishing
         "vscode-extension:esbuild",
+        // To ensure extension.js is regenerated even if
+        // vscode-extension:esbuild was already running in background
+        "vscode-extension:esbuild-notify",
         // Start the React app that is used in the extension
         "gui:dev"
       ],
@@ -36,6 +39,13 @@
         "isDefault": true
       }
     },
+    {
+      "label": "vscode-extension:esbuild-notify",
+      "dependsOn": ["vscode-extension:esbuild"],
+      "type": "npm",
+      "script": "esbuild-notify",
+      "path": "extensions/vscode"
+    },
     {
       "label": "vscode-extension:esbuild",
       "dependsOn": ["vscode-extension:continue-ui:build"],

extensions/vscode/package.json

@@ -602,6 +602,7 @@
     "vscode:prepublish": "npm run esbuild-base -- --minify",
     "esbuild": "npm run esbuild-base -- --sourcemap",
     "esbuild-watch": "npm run esbuild-base -- --sourcemap --watch",
+    "esbuild-notify": "npm run esbuild-base -- --sourcemap --notify",
     "esbuild:visualize": "esbuild-visualizer --metadata ./build/meta.json --filename ./build/stats.html --open",
     "tsc": "tsc -p ./",
     "tsc:check": "tsc -p ./ --noEmit",

extensions/vscode/scripts/esbuild.js

@@ -1,4 +1,5 @@
 const esbuild = require("esbuild");
+const fs = require("fs");
 
 const flags = process.argv.slice(2);
 
@@ -31,7 +32,6 @@ const esbuildConfig = {
             throw new Error(result.errors);
           } else {
             try {
-              const fs = require("fs");
               fs.writeFileSync(
                 "./build/meta.json",
                 JSON.stringify(result.metafile, null, 2),
@@ -52,6 +52,28 @@ const esbuildConfig = {
   if (flags.includes("--watch")) {
     const ctx = await esbuild.context(esbuildConfig);
     await ctx.watch();
+  } else if (flags.includes("--notify")) {
+    const inFile = esbuildConfig.entryPoints[0];
+    const outFile = esbuildConfig.outfile;
+
+    // The watcher automatically notices changes to source files
+    // so the only thing it needs to be notified about is if the
+    // output file gets removed.
+    if (fs.existsSync (outFile)) {
+        console.log("VS Code Extension esbuild up to date");
+        return;
+    }
+
+    fs.watchFile(outFile, (current, previous) => {
+      if (current.size > 0) {
+        console.log("VS Code Extension esbuild rebuild complete");
+        fs.unwatchFile(outFile);
+        process.exit(0);
+      }
+    });
+
+    console.log("Triggering VS Code Extension esbuild rebuild...");
+    fs.utimesSync(inFile, new Date(), new Date());
   } else {
     await esbuild.build(esbuildConfig);
   }