Skip base image inspection when a named build context provides it

src/spec-node/dockerCompose.ts

@@ -145,10 +145,22 @@ export function getBuildInfoForService(composeService: any, cliHostPath: typeof
 			context: (composeBuild.context as string | undefined) ?? cliHostPath.dirname(localComposeFiles[0]),
 			target: composeBuild.target as string | undefined,
 			args: composeBuild.args as Record<string, string> | undefined,
+			additionalContexts: toAdditionalContextsMap(composeBuild.additional_contexts),
 		}
 	};
 }
 
+// Compose accepts both a mapping and a list of 'name=value' entries.
+function toAdditionalContextsMap(additionalContexts: Record<string, string> | string[] | undefined) {
+	if (!Array.isArray(additionalContexts)) {
+		return additionalContexts;
+	}
+	return Object.fromEntries(additionalContexts.map(entry => {
+		const i = entry.indexOf('=');
+		return i === -1 ? [entry, ''] : [entry.slice(0, i), entry.slice(i + 1)];
+	}));
+}
+
 export async function buildAndExtendDockerCompose(configWithRaw: SubstitutedConfig<DevContainerFromDockerComposeConfig>, projectName: string, params: DockerResolverParameters, localComposeFiles: string[], envFile: string | undefined, composeGlobalArgs: string[], runServices: string[], noCache: boolean, overrideFilePath: string, overrideFilePrefix: string, versionPrefix: string, additionalFeatures: Record<string, string | boolean | Record<string, string | boolean>>, canAddLabelsToContainer: boolean, additionalCacheFroms?: string[], noBuild?: boolean) {
 
 	const { common, dockerCLI, dockerComposeCLI: dockerComposeCLIFunc } = params;
@@ -181,7 +193,7 @@ export async function buildAndExtendDockerCompose(configWithRaw: SubstitutedConf
 				dockerfile = modifiedDockerfile;
 			}
 		}
-		imageBuildInfo = await getImageBuildInfoFromDockerfile(params, originalDockerfile, serviceInfo.build?.args || {}, serviceInfo.build?.target, configWithRaw.substitute);
+		imageBuildInfo = await getImageBuildInfoFromDockerfile(params, originalDockerfile, serviceInfo.build?.args || {}, serviceInfo.build?.target, configWithRaw.substitute, Object.keys(serviceInfo.build.additionalContexts || {}));
 	} else {
 		imageBuildInfo = await getImageBuildInfoFromImage(params, composeService.image, configWithRaw.substitute);
 	}

src/spec-node/dockerfileUtils.ts

@@ -119,6 +119,15 @@ export function findBaseImage(dockerfile: Dockerfile, buildArgs: Record<string,
 	return undefined;
 }
 
+// BuildKit looks up named build contexts by the familiar image reference without ':latest'.
+export function isNamedBuildContext(image: string, buildContextNames: string[]) {
+	const familiar = image
+		.replace(/^(?:index\.)?docker\.io\//, '')
+		.replace(/^library\/(?=[^/]+$)/, '')
+		.replace(/:latest$/, '');
+	return buildContextNames.includes(familiar);
+}
+
 function extractDirectives(preambleStr: string) {
 	const map: Record<string, string> = {};
 	for (const line of preambleStr.split(/\r?\n/)) {

src/spec-node/imageMetadata.ts

@@ -11,7 +11,7 @@ import { Feature, FeaturesConfig, Mount, parseMount, SchemaFeatureLifecycleHooks
 import { ContainerDetails, DockerCLIParameters, ImageDetails } from '../spec-shutdown/dockerUtils';
 import { Log, LogLevel } from '../spec-utils/log';
 import { getBuildInfoForService, readDockerComposeConfig } from './dockerCompose';
-import { Dockerfile, extractDockerfile, findBaseImage, findUserStatement } from './dockerfileUtils';
+import { Dockerfile, extractDockerfile, findBaseImage, findUserStatement, isNamedBuildContext } from './dockerfileUtils';
 import { SubstituteConfig, SubstitutedConfig, DockerResolverParameters, inspectDockerImage, uriToWSLFsPath, envListToObj } from './utils';
 
 const pickConfigProperties: (keyof DevContainerConfig & keyof ImageMetadataEntry)[] = [
@@ -365,7 +365,7 @@ export async function getImageBuildInfo(params: DockerResolverParameters | Docke
 			const { context, dockerfilePath } = serviceInfo.build;
 			const resolvedDockerfilePath = cliHost.path.isAbsolute(dockerfilePath) ? dockerfilePath : cliHost.path.resolve(context, dockerfilePath);
 			const dockerfile = (await cliHost.readFile(resolvedDockerfilePath)).toString();
-			return getImageBuildInfoFromDockerfile(params, dockerfile, serviceInfo.build.args || {}, serviceInfo.build.target, configWithRaw.substitute);
+			return getImageBuildInfoFromDockerfile(params, dockerfile, serviceInfo.build.args || {}, serviceInfo.build.target, configWithRaw.substitute, Object.keys(serviceInfo.build.additionalContexts || {}));
 		} else {
 			return getImageBuildInfoFromImage(params, composeService.image, configWithRaw.substitute);
 		}
@@ -393,13 +393,13 @@ export async function getImageBuildInfoFromImage(params: DockerResolverParameter
 	};
 }
 
-export async function getImageBuildInfoFromDockerfile(params: DockerResolverParameters | DockerCLIParameters, dockerfile: string, dockerBuildArgs: Record<string, string>, targetStage: string | undefined, substitute: SubstituteConfig) {
+export async function getImageBuildInfoFromDockerfile(params: DockerResolverParameters | DockerCLIParameters, dockerfile: string, dockerBuildArgs: Record<string, string>, targetStage: string | undefined, substitute: SubstituteConfig, buildContextNames: string[] = []) {
 	const { output } = 'output' in params ? params : params.common;
 	const omitSyntaxDirective = 'common' in params ? !!params.common.omitSyntaxDirective : false;
-	return internalGetImageBuildInfoFromDockerfile(imageName => inspectDockerImage(params, imageName, true), dockerfile, dockerBuildArgs, targetStage, substitute, output, omitSyntaxDirective, params.buildPlatformInfo, params.targetPlatformInfo);
+	return internalGetImageBuildInfoFromDockerfile(imageName => inspectDockerImage(params, imageName, true), dockerfile, dockerBuildArgs, targetStage, substitute, output, omitSyntaxDirective, params.buildPlatformInfo, params.targetPlatformInfo, buildContextNames);
 }
 
-export async function internalGetImageBuildInfoFromDockerfile(inspectDockerImage: (imageName: string) => Promise<ImageDetails>, dockerfileText: string, dockerBuildArgs: Record<string, string>, targetStage: string | undefined, substitute: SubstituteConfig, output: Log, omitSyntaxDirective: boolean, buildPlatform: PlatformInfo, targetPlatform: PlatformInfo): Promise<ImageBuildInfo> {
+export async function internalGetImageBuildInfoFromDockerfile(inspectDockerImage: (imageName: string) => Promise<ImageDetails>, dockerfileText: string, dockerBuildArgs: Record<string, string>, targetStage: string | undefined, substitute: SubstituteConfig, output: Log, omitSyntaxDirective: boolean, buildPlatform: PlatformInfo, targetPlatform: PlatformInfo, buildContextNames: string[] = []): Promise<ImageBuildInfo> {
 	const dockerfile = extractDockerfile(dockerfileText);
 	if (dockerfile.preamble.directives.syntax && omitSyntaxDirective) {
 		output.write(`Omitting syntax directive '${dockerfile.preamble.directives.syntax}' from Dockerfile.`, LogLevel.Trace);
@@ -425,7 +425,12 @@ export async function internalGetImageBuildInfoFromDockerfile(inspectDockerImage
 		TARGETVARIANT: targetPlatform.variant ?? "",
 	};
 	const baseImage = findBaseImage(dockerfile, dockerBuildArgs, targetStage, globalBuildxPlatformArgs);
-	const imageDetails = baseImage && await inspectDockerImage(baseImage) || undefined;
+	// A named build context replaces the image at build time, so the reference may not exist locally or in any registry.
+	const fromBuildContext = !!baseImage && isNamedBuildContext(baseImage, buildContextNames);
+	if (fromBuildContext) {
+		output.write(`Not inspecting base image '${baseImage}' because a named build context provides it.`);
+	}
+	const imageDetails = baseImage && !fromBuildContext && await inspectDockerImage(baseImage) || undefined;
 	const dockerfileUser = findUserStatement(dockerfile, dockerBuildArgs, envListToObj(imageDetails?.Config.Env), globalBuildxPlatformArgs, targetStage);
 	const user = dockerfileUser || imageDetails?.Config.User || 'root';
 	const metadata = imageDetails ? getImageMetadata(imageDetails, substitute, output) : { config: [], raw: [], substitute };

src/test/dockerComposeUtils.test.ts

@@ -21,6 +21,8 @@ build:
   target: a-target
   args:
     arg1: value1
+  additional_contexts:
+    base: service:base
 `;
         const info = loadYamlAndGetBuildInfoForService(input);
         assert.deepEqual(info, {
@@ -32,10 +34,26 @@ build:
                 args: {
                     arg1: 'value1',
                 },
+                additionalContexts: {
+                    base: 'service:base',
+                },
             }
         });
     });
 
+    it('Parses additional_contexts in list form', () => {
+        const input = `
+build:
+  context: ./a-path
+  additional_contexts:
+    - base=docker-image://alpine:3.20
+`;
+        const info = loadYamlAndGetBuildInfoForService(input);
+        assert.deepEqual(info.build?.additionalContexts, {
+            base: 'docker-image://alpine:3.20',
+        });
+    });
+
     it('Parses image-only info', () => {
         const input = `
 image: my-image
@@ -74,6 +92,7 @@ build:
                 dockerfilePath: 'Dockerfile',
                 target: undefined,
                 args: undefined,
+                additionalContexts: undefined,
             }
         });
     });
@@ -91,6 +110,7 @@ build:
                 dockerfilePath: 'my-dockerfile',
                 target: undefined,
                 args: undefined,
+                additionalContexts: undefined,
             }
         });
     });

src/test/dockerfileUtils.test.ts

@@ -1,6 +1,6 @@
 import { assert, expect } from 'chai';
 import { imageMetadataLabel, internalGetImageBuildInfoFromDockerfile } from '../spec-node/imageMetadata';
-import { ensureDockerfileHasFinalStageName, extractDockerfile, findBaseImage, findUserStatement, supportsBuildContexts } from '../spec-node/dockerfileUtils';
+import { ensureDockerfileHasFinalStageName, extractDockerfile, findBaseImage, findUserStatement, isNamedBuildContext, supportsBuildContexts } from '../spec-node/dockerfileUtils';
 import { ImageDetails } from '../spec-shutdown/dockerUtils';
 import { nullLog } from '../spec-utils/log';
 import { testSubstitute } from './testUtils';
@@ -242,6 +242,59 @@ FROM base-\${TARGETARCH}
         assert.strictEqual(info.metadata.config.length, 0);
         assert.strictEqual(info.metadata.raw.length, 0);
     });
+
+    it('for a base image provided by a named build context', async () => {
+        const dockerfile = `FROM local-base
+USER dockerfileUser
+`;
+        const info = await internalGetImageBuildInfoFromDockerfile(async (imageName) => {
+            assert.fail(`Unexpected inspection of ${imageName}`);
+        }, dockerfile, {}, undefined, testSubstitute, nullLog, false, { os: 'linux', arch: 'amd64' }, { os: 'linux', arch: 'amd64' }, ['local-base']);
+        assert.strictEqual(info.user, 'dockerfileUser');
+        assert.strictEqual(info.metadata.config.length, 0);
+        assert.strictEqual(info.metadata.raw.length, 0);
+    });
+
+    it('for a base image not provided by the named build contexts', async () => {
+        const dockerfile = `FROM ubuntu:latest
+`;
+        const details: ImageDetails = {
+            Id: '123',
+            Config: {
+                User: 'imageUser',
+                Env: null,
+                Labels: null,
+                Entrypoint: null,
+                Cmd: null
+            },
+            Os: 'linux',
+            Architecture: 'amd64'
+        };
+        const info = await internalGetImageBuildInfoFromDockerfile(async (imageName) => {
+            assert.strictEqual(imageName, 'ubuntu:latest');
+            return details;
+        }, dockerfile, {}, undefined, testSubstitute, nullLog, false, { os: 'linux', arch: 'amd64' }, { os: 'linux', arch: 'amd64' }, ['local-base']);
+        assert.strictEqual(info.user, 'imageUser');
+    });
+});
+
+describe('isNamedBuildContext', () => {
+
+    it('matches the familiar reference form BuildKit uses', () => {
+        assert.isTrue(isNamedBuildContext('local-base', ['local-base']));
+        assert.isTrue(isNamedBuildContext('local-base:latest', ['local-base']));
+        assert.isTrue(isNamedBuildContext('docker.io/library/alpine', ['alpine']));
+        assert.isTrue(isNamedBuildContext('library/alpine:latest', ['alpine']));
+        assert.isTrue(isNamedBuildContext('docker.io/org/image:1.0', ['org/image:1.0']));
+        assert.isTrue(isNamedBuildContext('ghcr.io/org/image', ['ghcr.io/org/image']));
+    });
+
+    it('does not match other references', () => {
+        assert.isFalse(isNamedBuildContext('local-base:1.0', ['local-base']));
+        assert.isFalse(isNamedBuildContext('ghcr.io/org/image', ['org/image']));
+        assert.isFalse(isNamedBuildContext('library/org/image', ['org/image']));
+        assert.isFalse(isNamedBuildContext('local-base', []));
+    });
 });
 
 describe('findBaseImage', () => {