feat: allow custom build context to be configured when using DOCKERFILE_PATH

Makefile

@@ -11,6 +11,9 @@ build: scripts/envbuilder-$(GOARCH)
 test: test-registry test-images
 	go test -count=1 ./...
 
+test-race:
+	go test -race -count=3 ./...
+
 # Starts a local Docker registry on port 5000 with a local disk cache.
 .PHONY: test-registry
 test-registry: .registry-cache

envbuilder.go

@@ -139,6 +139,10 @@ type Options struct {
 	// to using a devcontainer that some might find simpler.
 	DockerfilePath string `env:"DOCKERFILE_PATH"`
 
+	// BuildContextPath can be specified when a DockerfilePath is specified outside the base WorkspaceFolder.
+	// This path MUST be relative to the WorkspaceFolder path into which the repo is cloned.
+	BuildContextPath string `env:"BUILD_CONTEXT_PATH"`
+
 	// CacheTTLDays is the number of days to use cached layers before
 	// expiring them. Defaults to 7 days.
 	CacheTTLDays int `env:"CACHE_TTL_DAYS"`
@@ -476,7 +480,7 @@ func Run(ctx context.Context, options Options) error {
 			buildParams = &devcontainer.Compiled{
 				DockerfilePath:    dockerfilePath,
 				DockerfileContent: string(content),
-				BuildContext:      options.WorkspaceFolder,
+				BuildContext:      filepath.Join(options.WorkspaceFolder, options.BuildContextPath),
 			}
 		}
 	}

integration/integration_test.go

@@ -719,6 +719,91 @@ func TestNoMethodFails(t *testing.T) {
 	require.ErrorContains(t, err, envbuilder.ErrNoFallbackImage.Error())
 }
 
+func TestDockerfileBuildContext(t *testing.T) {
+	t.Parallel()
+
+	inclFile := "myfile"
+	dockerfile := fmt.Sprintf(`FROM %s
+COPY %s .`, testImageAlpine, inclFile)
+
+	tests := []struct {
+		name             string
+		files            map[string]string
+		dockerfilePath   string
+		buildContextPath string
+		expectedErr      string
+	}{
+		{
+			// Dockerfile & build context are in the same dir, copying inclFile should work.
+			name: "same build context (default)",
+			files: map[string]string{
+				"Dockerfile": dockerfile,
+				inclFile:     "...",
+			},
+			dockerfilePath:   "Dockerfile",
+			buildContextPath: "", // use default
+			expectedErr:      "", // expect no errors
+		},
+		{
+			// Dockerfile & build context are not in the same dir, build context is still the default; this should fail
+			// to copy inclFile since it is not in the same dir as the Dockerfile.
+			name: "different build context (default)",
+			files: map[string]string{
+				"a/Dockerfile":  dockerfile,
+				"a/" + inclFile: "...",
+			},
+			dockerfilePath:   "a/Dockerfile",
+			buildContextPath: "", // use default
+			expectedErr:      inclFile + ": no such file or directory",
+		},
+		{
+			// Dockerfile & build context are not in the same dir, but inclFile is in the default build context dir;
+			// this should allow inclFile to be copied. This is probably not desirable though?
+			name: "different build context (default, different content roots)",
+			files: map[string]string{
+				"a/Dockerfile": dockerfile,
+				inclFile:       "...",
+			},
+			dockerfilePath:   "a/Dockerfile",
+			buildContextPath: "", // use default
+			expectedErr:      "",
+		},
+		{
+			// Dockerfile is not in the default build context dir, but the build context has been overridden; this should
+			// allow inclFile to be copied.
+			name: "different build context (custom)",
+			files: map[string]string{
+				"a/Dockerfile":  dockerfile,
+				"a/" + inclFile: "...",
+			},
+			dockerfilePath:   "a/Dockerfile",
+			buildContextPath: "a/",
+			expectedErr:      "",
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			url := createGitServer(t, gitServerOptions{
+				files: tc.files,
+			})
+			_, err := runEnvbuilder(t, options{env: []string{
+				"GIT_URL=" + url,
+				"DOCKERFILE_PATH=" + tc.dockerfilePath,
+				"BUILD_CONTEXT_PATH=" + tc.buildContextPath,
+			}})
+
+			if tc.expectedErr == "" {
+				require.NoError(t, err)
+			} else {
+				require.ErrorContains(t, err, tc.expectedErr)
+			}
+		})
+	}
+}
+
 // TestMain runs before all tests to build the envbuilder image.
 func TestMain(m *testing.M) {
 	cleanOldEnvbuilders()