[CDTOOL-691] Better error reporting when JavaScript tools are missing

CHANGELOG.md

@@ -220,6 +220,8 @@ both the old and new forms are:
 - feat(service/resourcelink): moved the `resource-link` commands under the `service` command, with an unlisted and deprecated alias of `resource-link` ([#1635](https://github.com/fastly/cli/pull/1635))
 - feat(service/logging): moved the `logging` commands under the `service` command, with an unlisted and deprecated alias of `logging` ([#1642](https://github.com/fastly/cli/pull/1642))
 - feat(service/auth): moved the `service-auth` commands under the `service` command and renamed to `auth`, with an unlisted and deprecated alias of `service-auth` ([#1643](https://github.com/fastly/cli/pull/1643))
+- feat(compute/build): improved error messaging for JavaScript builds with pre-flight toolchain verification including Bun runtime support ([#1640](https://github.com/fastly/cli/pull/1640))
+
 ### Bug fixes:
 
 - fix(docker): Use base image toolchain instead of reinstalling stable, which could pull in an unvalidated Rust version.

pkg/commands/compute/build_test.go

@@ -513,6 +513,7 @@ func TestBuildJavaScript(t *testing.T) {
 		// default build script inserted.
 		//
 		// NOTE: This test passes --verbose so we can validate specific outputs.
+		// NOTE: npmInstall is required because toolchain verification checks for node_modules.
 		{
 			name: "build script inserted dynamically when missing",
 			args: args("compute build --verbose"),
@@ -523,8 +524,8 @@ func TestBuildJavaScript(t *testing.T) {
 			wantOutput: []string{
 				"No [scripts.build] found in fastly.toml.", // requires --verbose
 				"The following default build command for",
-				"npm exec webpack", // our testdata package.json references webpack
 			},
+			npmInstall: true,
 		},
 		{
 			name: "build error",
@@ -548,7 +549,7 @@ func TestBuildJavaScript(t *testing.T) {
 			language = "javascript"
 
       [scripts]
-      build = "%s"`, compute.JsDefaultBuildCommandForWebpack),
+      build = "%s"`, compute.JsDefaultBuildCommand),
 			wantOutput: []string{
 				"Creating ./bin directory (for Wasm binary)",
 				"Built package",
@@ -591,7 +592,6 @@ func TestBuildJavaScript(t *testing.T) {
 				T: t,
 				Copy: []testutil.FileIO{
 					{Src: filepath.Join("testdata", "build", "javascript", "package.json"), Dst: "package.json"},
-					{Src: filepath.Join("testdata", "build", "javascript", "webpack.config.js"), Dst: "webpack.config.js"},
 					{Src: filepath.Join("testdata", "build", "javascript", "src", "index.js"), Dst: filepath.Join("src", "index.js")},
 				},
 				Write: []testutil.FileIO{