fix: validate buildx and imageName early for mergeTag, guard empty imageName

- Move isDockerBuildXInstalled() before the mergeTag early return so
  missing buildx fails immediately with a clear error instead of at
  runtime in the post step.
- Validate imageName is set when mergeTag is used.
- Guard buildImageNames calls so empty imageName produces [] instead
  of invalid image refs like ':latest'.

Author: tgenov

azdo-task/DevcontainersCi/src/main.ts

@@ -36,7 +36,24 @@ export async function runMain(): Promise<void> {
 			return;
 		}
 
+		const buildXInstalled = await isDockerBuildXInstalled();
+
 		if (mergeTag) {
+			const imageName = task.getInput('imageName');
+			if (!imageName) {
+				task.setResult(
+					task.TaskResult.Failed,
+					'imageName is required when using mergeTag',
+				);
+				return;
+			}
+			if (!buildXInstalled) {
+				task.setResult(
+					task.TaskResult.Failed,
+					'docker buildx is required for mergeTag - add a step to set up docker buildx',
+				);
+				return;
+			}
 			const pushOption = task.getInput('push');
 			if (pushOption !== 'always') {
 				task.setResult(
@@ -51,8 +68,6 @@ export async function runMain(): Promise<void> {
 			task.setTaskVariable('mergeTag', mergeTag);
 			return;
 		}
-
-		const buildXInstalled = await isDockerBuildXInstalled();
 		if (!buildXInstalled) {
 			console.log(
 				'### WARNING: docker buildx not available: add a step to set up with docker/setup-buildx-action - see https://github.com/devcontainers/ci/blob/main/docs/azure-devops-task.md',
@@ -113,11 +128,9 @@ export async function runMain(): Promise<void> {
 
 		const resolvedImageTag = imageTag ?? 'latest';
 		const imageTagArray = resolvedImageTag.split(/\s*,\s*/);
-		const fullImageNameArray = buildImageNames(
-			imageName ?? '',
-			imageTagArray,
-			platformTag,
-		);
+		const fullImageNameArray = imageName
+			? buildImageNames(imageName, imageTagArray, platformTag)
+			: [];
 		if (imageName) {
 			if (fullImageNameArray.length === 1) {
 				if (!noCache && !cacheFrom.includes(fullImageNameArray[0])) {

github-action/dist/index.js

@@ -2171,7 +2171,17 @@ function runMain() {
                 core.setFailed('mergeTag and platformTag cannot be used together - mergeTag is for the manifest merge job, platformTag is for per-platform build jobs');
                 return;
             }
+            const buildXInstalled = yield (0, docker_1.isDockerBuildXInstalled)();
             if (mergeTag) {
+                const imageName = emptyStringAsUndefined(core.getInput('imageName'));
+                if (!imageName) {
+                    core.setFailed('imageName is required when using mergeTag');
+                    return;
+                }
+                if (!buildXInstalled) {
+                    core.setFailed('docker buildx is required for mergeTag - add a step to set up with docker/setup-buildx-action');
+                    return;
+                }
                 const pushOption = emptyStringAsUndefined(core.getInput('push'));
                 if (pushOption !== 'always') {
                     core.setFailed("push must be set to 'always' when using mergeTag - the manifest merge job must push the resulting multi-arch image");
@@ -2181,7 +2191,6 @@ function runMain() {
                 core.saveState('mergeTag', mergeTag);
                 return;
             }
-            const buildXInstalled = yield (0, docker_1.isDockerBuildXInstalled)();
             if (!buildXInstalled) {
                 core.warning('docker buildx not available: add a step to set up with docker/setup-buildx-action - see https://github.com/devcontainers/ci/blob/main/docs/github-action.md');
                 return;
@@ -2230,7 +2239,9 @@ function runMain() {
             const configFile = relativeConfigFile && path_1.default.resolve(checkoutPath, relativeConfigFile);
             const resolvedImageTag = imageTag !== null && imageTag !== void 0 ? imageTag : 'latest';
             const imageTagArray = resolvedImageTag.split(/\s*,\s*/);
-            const fullImageNameArray = (0, platform_1.buildImageNames)(imageName !== null && imageName !== void 0 ? imageName : '', imageTagArray, platformTag);
+            const fullImageNameArray = imageName
+                ? (0, platform_1.buildImageNames)(imageName, imageTagArray, platformTag)
+                : [];
             if (imageName) {
                 if (fullImageNameArray.length === 1) {
                     if (!noCache && !cacheFrom.includes(fullImageNameArray[0])) {

github-action/dist/index.js.map

@@ -45,7 +45,20 @@ export async function runMain(): Promise<void> {
 			return;
 		}
 
+		const buildXInstalled = await isDockerBuildXInstalled();
+
 		if (mergeTag) {
+			const imageName = emptyStringAsUndefined(core.getInput('imageName'));
+			if (!imageName) {
+				core.setFailed('imageName is required when using mergeTag');
+				return;
+			}
+			if (!buildXInstalled) {
+				core.setFailed(
+					'docker buildx is required for mergeTag - add a step to set up with docker/setup-buildx-action',
+				);
+				return;
+			}
 			const pushOption = emptyStringAsUndefined(core.getInput('push'));
 			if (pushOption !== 'always') {
 				core.setFailed(
@@ -59,8 +72,6 @@ export async function runMain(): Promise<void> {
 			core.saveState('mergeTag', mergeTag);
 			return;
 		}
-
-		const buildXInstalled = await isDockerBuildXInstalled();
 		if (!buildXInstalled) {
 			core.warning(
 				'docker buildx not available: add a step to set up with docker/setup-buildx-action - see https://github.com/devcontainers/ci/blob/main/docs/github-action.md',
@@ -123,11 +134,9 @@ export async function runMain(): Promise<void> {
 
 		const resolvedImageTag = imageTag ?? 'latest';
 		const imageTagArray = resolvedImageTag.split(/\s*,\s*/);
-		const fullImageNameArray = buildImageNames(
-			imageName ?? '',
-			imageTagArray,
-			platformTag,
-		);
+		const fullImageNameArray = imageName
+			? buildImageNames(imageName, imageTagArray, platformTag)
+			: [];
 		if (imageName) {
 			if (fullImageNameArray.length === 1) {
 				if (!noCache && !cacheFrom.includes(fullImageNameArray[0])) {