For Podman, invoke host cpp when available and fail clearly otherwise,

Author: Mathiyarasy

src/spec-node/dockerCompose.ts

@@ -18,7 +18,7 @@ import { getExtendImageBuildInfo, updateRemoteUserUID } from './containerFeature
 import { Mount, parseMount } from '../spec-configuration/containerFeaturesConfiguration';
 import path from 'path';
 import { getDevcontainerMetadata, getImageBuildInfoFromDockerfile, getImageBuildInfoFromImage, getImageMetadataFromContainer, ImageBuildInfo, lifecycleCommandOriginMapFromMetadata, mergeConfiguration, MergedDevContainerConfig } from './imageMetadata';
-import { ensureDockerfileHasFinalStageName } from './dockerfileUtils';
+import { ensureDockerfileHasFinalStageName, preprocessDockerfileIn } from './dockerfileUtils';
 import { randomUUID } from 'crypto';
 
 const projectLabel = 'com.docker.compose.project';
@@ -167,7 +167,10 @@ export async function buildAndExtendDockerCompose(configWithRaw: SubstitutedConf
 	if (serviceInfo.build) {
 		const { context, dockerfilePath, target } = serviceInfo.build;
 		const resolvedDockerfilePath = cliHost.path.isAbsolute(dockerfilePath) ? dockerfilePath : path.resolve(context, dockerfilePath);
-		const originalDockerfile = (await cliHost.readFile(resolvedDockerfilePath)).toString();
+		let originalDockerfile = (await cliHost.readFile(resolvedDockerfilePath)).toString();
+		if (params.isPodman && resolvedDockerfilePath.endsWith('.in')) {
+			originalDockerfile = await preprocessDockerfileIn(resolvedDockerfilePath, cliHost.exec, output);
+		}
 		dockerfile = originalDockerfile;
 		if (target) {
 			// Explictly set build target for the dev container build features on that

src/spec-node/dockerfileUtils.ts

@@ -4,6 +4,8 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as semver from 'semver';
+import { ExecFunction, runCommandNoPty } from '../spec-common/commonUtils';
+import { Log } from '../spec-utils/log';
 import { Mount } from '../spec-configuration/containerFeaturesConfiguration';
 
 
@@ -260,6 +262,37 @@ export function ensureDockerfileHasFinalStageName(dockerfile: string, defaultLas
 	return { lastStageName: defaultLastStageName, modifiedDockerfile: modifiedDockerfile };
 }
 
+/**
+ * Preprocess a Dockerfile.in file using the host cpp tool.
+ * This is needed when using Podman, which supports cpp preprocessing of .in files natively.
+ * Throws a clear error if cpp is not available on the host.
+ */
+export async function preprocessDockerfileIn(dockerfilePath: string, exec: ExecFunction, output: Log): Promise<string> {
+	let result: { stdout: Buffer; stderr: Buffer };
+	try {
+		result = await runCommandNoPty({
+			exec,
+			cmd: 'cpp',
+			// -undef:               do not predefine platform/compiler macros
+			// -fdirectives-only:    only process directives, do not expand macros
+			// -w:                   suppress warnings
+			// -P:                   suppress linemarker output lines
+			args: ['-undef', '-fdirectives-only', '-w', '-P', dockerfilePath],
+			output,
+		});
+	} catch (err: any) {
+		if (err?.code === 'ENOENT' || err?.message?.includes('ENOENT')) {
+			throw new Error(
+				`Preprocessing '${dockerfilePath}' requires 'cpp', but it was not found on the host. ` +
+				`Please install cpp (e.g. "sudo apt-get install cpp") to use Dockerfile.in files with Podman.`
+			);
+		}
+		const stderrText = err?.stderr ? `\n${(err.stderr as Buffer).toString()}` : '';
+		throw new Error(`Failed to preprocess '${dockerfilePath}' using cpp: ${err?.message || String(err)}${stderrText}`);
+	}
+	return result.stdout.toString();
+}
+
 export function supportsBuildContexts(dockerfile: Dockerfile) {
 	const version = dockerfile.preamble.version;
 	if (!version) {

src/spec-node/singleContainer.ts

@@ -12,7 +12,7 @@ import { DevContainerConfig, DevContainerFromDockerfileConfig, DevContainerFromI
 import { LogLevel, Log, makeLog } from '../spec-utils/log';
 import { extendImage, getExtendImageBuildInfo, updateRemoteUserUID } from './containerFeatures';
 import { getDevcontainerMetadata, getImageBuildInfoFromDockerfile, getImageMetadataFromContainer, ImageMetadataEntry, lifecycleCommandOriginMapFromMetadata, mergeConfiguration, MergedDevContainerConfig } from './imageMetadata';
-import { ensureDockerfileHasFinalStageName, generateMountCommand } from './dockerfileUtils';
+import { ensureDockerfileHasFinalStageName, generateMountCommand, preprocessDockerfileIn } from './dockerfileUtils';
 
 export const hostFolderLabel = 'devcontainer.local_folder'; // used to label containers created from a workspace/folder
 export const configFileLabel = 'devcontainer.config_file';
@@ -131,6 +131,9 @@ async function buildAndExtendImage(buildParams: DockerResolverParameters, config
 	}
 
 	let dockerfile = (await cliHost.readFile(dockerfilePath)).toString();
+	if (buildParams.isPodman && dockerfilePath.endsWith('.in')) {
+		dockerfile = await preprocessDockerfileIn(dockerfilePath, cliHost.exec, output);
+	}
 	const originalDockerfile = dockerfile;
 	let baseName = 'dev_container_auto_added_stage_label';
 	if (config.build?.target) {

src/test/configs/podman-with-cpp/.devcontainer.json

@@ -0,0 +1,10 @@
+{
+	"build": {
+		"dockerfile": "Dockerfile.in"
+	},
+	"features": {
+		"ghcr.io/devcontainers/features/github-cli:1": {
+			"version": "latest"
+		}
+	}
+}

src/test/configs/podman-with-cpp/Dockerfile.in

@@ -0,0 +1,16 @@
+#define BASE_IMAGE ubuntu:20.04
+#define INSTALL_NODE
+#define INSTALL_PYTHON
+
+FROM BASE_IMAGE
+
+#ifdef INSTALL_NODE
+RUN apt-get update && apt-get install -y nodejs
+#endif
+
+#ifdef INSTALL_PYTHON
+RUN apt-get update && apt-get install -y python3
+#endif
+
+#include "common.Dockerfile"
+#include "tools.Dockerfile"

src/test/configs/podman-with-cpp/common.Dockerfile

@@ -0,0 +1,4 @@
+RUN apt-get update && apt-get install -y curl wget
+
+ENV APP_ENV=development
+ENV APP_DEBUG=true

src/test/configs/podman-with-cpp/test.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+echo "hello! podman with cpp test"

src/test/configs/podman-with-cpp/tools.Dockerfile

@@ -0,0 +1,2 @@
+RUN apt-get update && apt-get install -y vim
+COPY ./test.sh /usr/local/bin/test.sh