style(pkg/common): improve code readability and maintainability

fix(makefile): Remove.DEFAULT_GOAL and.PHONY

fix(makefile): Refine the Makefile file so that it can do the basic work

Signed-off-by: Xinwei Xiong(cubxxw) <3293172751nss@gmail.com>

Makefile

@@ -1,8 +1,8 @@
 ifeq ($(OS),Windows_NT)
 SHELL:=cmd.exe
 
-# Need BLANK due to makefile parsing of `\\`
-# (see: <https://stackoverflow.com/questions/54733231/how-to-escape-a-backslash-in-the-end-to-mean-literal-backslash-in-makefile/54733416#54733416>)
+# Need BLANK due to makefile parsing of `\`
+# (see: https://stackoverflow.com/questions/54733231/how-to-escape-a-backslash-in-the-end-to-mean-literal-backslash-in-makefile/54733416#54733416)
 BLANK:=
 
 # Define variable named `/` to represent OS path separator (usable as `$/` in this file)
@@ -37,6 +37,14 @@ NO_DOCKER?=
 clean_build := $(strip ${PACK_BUILD})
 clean_sha := $(strip ${PACK_GITSHA1})
 
+# append coverage arguments
+ifeq ($(TEST_COVERAGE), 1)
+unit: GOTESTFLAGS:=$(GOTESTFLAGS) -coverprofile=./out/tests/coverage-unit.txt -covermode=atomic
+endif
+ifeq ($(NO_DOCKER),)
+unit: GOTESTFLAGS:=$(GOTESTFLAGS) --tags=example
+endif
+
 # Append build number and git sha to version, if not-empty
 ifneq ($(and $(clean_build),$(clean_sha)),)
 PACK_VERSION:=${PACK_VERSION}+git-${clean_sha}.build-${clean_build}
@@ -54,7 +62,9 @@ BINDIR:=/usr/bin/
 .DEFAULT_GOAL := build
 .PHONY: clean build format imports lint test unit acceptance prepare-for-pr verify verify-format benchmark 
 
-## bUild: Build the program
+# this target must be listed first in order for it to be a default target,
+# so that ubuntu_ppa's may be constructed using default build tools.
+## build: Build the program
 build: out
 	@echo "=====> Building..."
 	$(GOCMD) build -ldflags "-s -w -X 'github.com/buildpacks/pack.Version=${PACK_VERSION}' -extldflags ${LDFLAGS}" -trimpath -o ./out/$(PACK_BIN) -a ./cmd/pack
@@ -126,15 +136,19 @@ verify-format: install-goimports
 benchmark: out
 	@echo "=====> Running benchmarks"
 	$(GOCMD) test -run=^$  -bench=. -benchtime=1s -benchmem -memprofile=./out/bench_mem.out -cpuprofile=./out/bench_cpu.out -tags=benchmarks ./benchmarks/ -v
+# NOTE: You can analyze the results, using go tool pprof. For instance, you can start a server to see a graph of the cpu usage by running
+# go tool pprof -http=":8082" out/bench_cpu.out. Alternatively, you can run go tool pprof, and in the ensuing cli, run
+# commands like top10 or web to dig down into the cpu and memory usage
+# For more, see https://blog.golang.org/pprof
 
 ## package: Package the program
 package: out
 	tar czf .$/out$/$(ARCHIVE_NAME).tgz -C .$/out$/ $(PACK_BIN)
 
 ## install: Install the program to the system
 install:
-	mkdir -p ${DESTDIR}${BINDIR}
-	cp ./out/$(PACK_BIN) ${DESTDIR}${BINDIR}/
+	@mkdir -p ${DESTDIR}${BINDIR}
+	@cp ./out/$(PACK_BIN) ${DESTDIR}${BINDIR}/
 
 ## install-mockgen: Used only by apt-get install when installing ubuntu ppa
 install-mockgen:

pkg/client/common.go

@@ -18,7 +18,7 @@ func (c *Client) parseTagReference(imageName string) (name.Reference, error) {
 		return nil, errors.New("image is a required parameter")
 	}
 	if _, err := name.ParseReference(imageName, name.WeakValidation); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("'%s' is not a valid tag reference: %s", imageName, err)
 	}
 	ref, err := name.NewTag(imageName, name.WeakValidation)
 	if err != nil {
@@ -108,17 +108,14 @@ func contains(slc []string, v string) bool {
 }
 
 func getBestRunMirror(registry string, runImage string, mirrors []string, preferredMirrors []string) string {
-	var runImageList []string
-	runImageList = append(runImageList, preferredMirrors...)
-	runImageList = append(runImageList, runImage)
-	runImageList = append(runImageList, mirrors...)
+	runImageList := append(append(append([]string{}, preferredMirrors...), runImage), mirrors...)
 
 	for _, img := range runImageList {
 		ref, err := name.ParseReference(img, name.WeakValidation)
 		if err != nil {
 			continue
 		}
-		if ref.Context().RegistryStr() == registry {
+		if reg := ref.Context().RegistryStr(); reg == registry {
 			return img
 		}
 	}