Sets CNB_BUILDPACK_DIR in bp execution env during detect and build

* Resolves #320

Signed-off-by: Emily Casey <ecasey@vmware.com>

builder.go

@@ -111,6 +111,7 @@ func (b *Builder) Build() (*BuildMetadata, error) {
 				return nil, err
 			}
 		}
+		cmd.Env = append(cmd.Env, EnvBuildpackDir+"="+bpInfo.Path)
 
 		if err := cmd.Run(); err != nil {
 			return nil, err

builder_test.go

@@ -215,6 +215,26 @@ func testBuilder(t *testing.T, when spec.G, it spec.S) {
 				}
 			})
 
+			it("should set CNB_BUILDPACK_DIR", func() {
+				if _, err := builder.Build(); err != nil {
+					t.Fatalf("Unexpected error:\n%s\n", err)
+				}
+				bpsDir, err := filepath.Abs(builder.BuildpacksDir)
+				if err != nil {
+					t.Fatalf("Unexpected error:\n%s\n", err)
+				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-env-cnb-buildpack-dir-A-v1")),
+					filepath.Join(bpsDir, "A/v1"),
+				); s != "" {
+					t.Fatalf("Unexpected CNB_BUILDPACK_DIR:\n%s\n", s)
+				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-env-cnb-buildpack-dir-B-v2")),
+					filepath.Join(bpsDir, "B/v2"),
+				); s != "" {
+					t.Fatalf("Unexpected CNB_BUILDPACK_DIR:\n%s\n", s)
+				}
+			})
+
 			it("should connect stdout and stdin to the terminal", func() {
 				if _, err := builder.Build(); err != nil {
 					t.Fatalf("Unexpected error:\n%s\n", err)
@@ -363,13 +383,46 @@ func testBuilder(t *testing.T, when spec.G, it spec.S) {
 		})
 
 		when("building succeeds with a clear env", func() {
-			it("should not apply user-provided env vars", func() {
-				env.EXPECT().List().Return(append(os.Environ(), "TEST_ENV=Av1.clear"))
-				env.EXPECT().WithPlatform(platformDir).Return(append(os.Environ(), "TEST_ENV=Bv1"), nil)
+			it.Before(func() {
+				env.EXPECT().List().Return(append(os.Environ(), "TEST_ENV=cleared"))
+				env.EXPECT().WithPlatform(platformDir).Return(append(os.Environ(), "TEST_ENV=with-platform"), nil)
 				builder.Group.Group[0].Version = "v1.clear"
+			})
+
+			it("should not apply user-provided env vars", func() {
 				if _, err := builder.Build(); err != nil {
 					t.Fatalf("Error: %s\n", err)
 				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-info-A-v1.clear")),
+					"TEST_ENV: cleared\n",
+				); s != "" {
+					t.Fatalf("Unexpected info:\n%s\n", s)
+				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-info-B-v2")),
+					"TEST_ENV: with-platform\n",
+				); s != "" {
+					t.Fatalf("Unexpected info:\n%s\n", s)
+				}
+			})
+
+			it("should set CNB_BUILDPACK_DIR", func() {
+				if _, err := builder.Build(); err != nil {
+					t.Fatalf("Unexpected error:\n%s\n", err)
+				}
+				bpsDir, err := filepath.Abs(builder.BuildpacksDir)
+				if err != nil {
+					t.Fatalf("Unexpected error:\n%s\n", err)
+				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-env-cnb-buildpack-dir-A-v1.clear")),
+					filepath.Join(bpsDir, "A/v1.clear"),
+				); s != "" {
+					t.Fatalf("Unexpected CNB_BUILDPACK_DIR:\n%s\n", s)
+				}
+				if s := cmp.Diff(rdfile(t, filepath.Join(appDir, "build-env-cnb-buildpack-dir-B-v2")),
+					filepath.Join(bpsDir, "B/v2"),
+				); s != "" {
+					t.Fatalf("Unexpected CNB_BUILDPACK_DIR:\n%s\n", s)
+				}
 			})
 		})
 

detector.go

@@ -15,8 +15,9 @@ import (
 )
 
 const (
-	CodeDetectPass = 0
-	CodeDetectFail = 100
+	CodeDetectPass  = 0
+	CodeDetectFail  = 100
+	EnvBuildpackDir = "CNB_BUILDPACK_DIR"
 )
 
 var ErrFail = errors.New("no buildpacks participating")
@@ -221,6 +222,7 @@ func (bp *buildpackTOML) Detect(c *DetectConfig) detectRun {
 	if bp.Buildpack.ClearEnv {
 		cmd.Env = c.ClearEnv
 	}
+	cmd.Env = append(cmd.Env, EnvBuildpackDir+"="+bp.Path)
 
 	if err := cmd.Run(); err != nil {
 		if err, ok := err.(*exec.ExitError); ok {

detector_test.go

@@ -185,6 +185,34 @@ func testDetector(t *testing.T, when spec.G, it spec.S) {
 			}
 		})
 
+		it("should set CNB_BUILDPACK_DIR in the environment", func() {
+			mkappfile("0", "detect-status-A-v1.clear", "detect-status-B-v1")
+
+			_, _, err := lifecycle.BuildpackOrder{{
+				Group: []lifecycle.Buildpack{
+					{ID: "A", Version: "v1.clear"},
+					{ID: "B", Version: "v2"},
+				},
+			}}.Detect(config)
+			if err != nil {
+				t.Fatalf("Unexpected error:\n%s\n", err)
+			}
+
+			bpsDir, err := filepath.Abs(config.BuildpacksDir)
+			if err != nil {
+				t.Fatalf("Unexpected error:\n%s\n", err)
+			}
+			expectedBpDir := filepath.Join(bpsDir, "A/v1.clear")
+			if bpDir := rdappfile("detect-env-cnb-buildpack-dir-A-v1.clear"); bpDir != expectedBpDir {
+				t.Fatalf("Unexpected buildpack dir:\n\twanted: %s\n\tgot: %s\n", expectedBpDir, bpDir)
+			}
+
+			expectedBpDir = filepath.Join(bpsDir, "B/v2")
+			if bpDir := rdappfile("detect-env-cnb-buildpack-dir-B-v2"); bpDir != expectedBpDir {
+				t.Fatalf("Unexpected buildpack dir:\n\twanted: %s\n\tgot: %s\n", expectedBpDir, bpDir)
+			}
+		})
+
 		when("a build plan is employed", func() {
 			it("should return a build plan with matched dependencies", func() {
 				mkappfile("100", "detect-status-C-v1")

testdata/buildpack/bin/build

@@ -14,6 +14,7 @@ echo "build out: ${bp_id}@${bp_version}"
 >&2 echo "build err: ${bp_id}@${bp_version}"
 
 echo "TEST_ENV: ${TEST_ENV}" > "build-info-${bp_id}-${bp_version}"
+echo -n "${CNB_BUILDPACK_DIR:-unset}" > "build-env-cnb-buildpack-dir-${bp_id}-${bp_version}"
 
 cp -a "$platform_dir/env" "build-env-${bp_id}-${bp_version}"
 
@@ -38,4 +39,4 @@ if [[ -f build-status ]]; then
   exit "$(cat build-status)"
 fi
 
-exit 0
+exit 0

testdata/buildpack/bin/detect

@@ -14,6 +14,7 @@ echo "detect out: ${bp_id}@${bp_version}"
 
 ls -1 "$platform_dir/env" > "detect-env-${bp_id}-${bp_version}"
 echo -n "$ENV_TYPE" > "detect-env-type-${bp_id}-${bp_version}"
+echo -n "${CNB_BUILDPACK_DIR:-unset}" > "detect-env-cnb-buildpack-dir-${bp_id}-${bp_version}"
 
 if [[ -f detect-plan-${bp_id}-${bp_version}.toml ]]; then
   cat "detect-plan-${bp_id}-${bp_version}.toml" > "$plan_path"