Error when building a library target in serve mode

Author: devongovett

packages/core/core/src/requests/TargetRequest.js

@@ -372,6 +372,40 @@ export class TargetResolver {
           this.options.serveOptions.distDir,
         );
         let mainTarget = targets.length === 1 ? targets[0] : null;
+
+        if (mainTarget?.env.isLibrary) {
+          let loc = mainTarget.loc;
+          throw new ThrowableDiagnostic({
+            diagnostic: {
+              origin: '@parcel/core',
+              message: md`
+Library targets are not supported in serve mode.
+              `,
+              codeFrames: loc
+                ? [
+                    {
+                      filePath: fromProjectPath(
+                        this.options.projectRoot,
+                        loc.filePath,
+                      ),
+                      codeHighlights: [
+                        convertSourceLocationToHighlight(
+                          loc,
+                          'Target declared here',
+                        ),
+                      ],
+                    },
+                  ]
+                : [],
+              hints: [
+                `The "${mainTarget.name}" field is meant for libraries, not applications. Either remove the "${mainTarget.name}" field or choose a different target name.`,
+              ],
+              documentationURL:
+                'https://parceljs.org/features/targets/#library-targets',
+            },
+          });
+        }
+
         let context = mainTarget?.env.context ?? 'browser';
         let engines = BROWSER_ENVS.has(context)
           ? {browsers: DEFAULT_ENGINES.browsers}

packages/core/integration-tests/test/integration/sourcemap/package.json

@@ -3,9 +3,10 @@
   "version": "1.0.0",
   "license": "MIT",
   "private": true,
-  "browser": "dist/index.js",
+  "default": "dist/index.js",
   "targets": {
-    "browser": {
+    "default": {
+      "context": "browser",
       "engines": {
         "browsers": [
           "> 0.25%"

packages/core/integration-tests/test/sourcemaps.js

@@ -154,7 +154,11 @@ describe('sourcemaps', function () {
       __dirname,
       '/integration/sourcemap/index.js',
     );
-    await bundle(sourceFilename);
+    await bundle(sourceFilename, {
+      defaultTargetOptions: {
+        shouldScopeHoist: true,
+      },
+    });
 
     let distDir = path.join(__dirname, '/integration/sourcemap/dist/');
 
@@ -175,6 +179,7 @@ describe('sourcemaps', function () {
     let sourcePath = 'index.js';
 
     let name = raw.match(/function (\$.*\$var\$helloWorld)/)[1];
+    let exports = raw.match(/var (\$.*\$exports)/)[1];
 
     checkSourceMapping({
       map: sourceMap,
@@ -190,7 +195,7 @@ describe('sourcemaps', function () {
       source: input,
       generated: raw,
       str: 'module.exports = helloWorld;',
-      generatedStr: 'module.exports = ' + name + ';',
+      generatedStr: exports + ' = ' + name + ';',
       sourcePath,
     });