build: allow using cache explicitly with --squash-all using --layers

Buildah already supports using `--layers` with `--squash` after containers/buildah#3674
if user wants to do so hence podman must honor similar configuration
in `--squash-all` behaviour if user wants to using cache.

PS: We cannot alter behaviour of `podman build --squash` for
docker-compat reasons hence this feature can be easily supported by
`--squash-all`.

Closes: containers/buildah#4011

Signed-off-by: Aditya R <arajan@redhat.com>

cmd/podman/images/build.go

@@ -197,9 +197,8 @@ func buildFlags(cmd *cobra.Command) {
 // build executes the build command.
 func build(cmd *cobra.Command, args []string) error {
 	if (cmd.Flags().Changed("squash") && cmd.Flags().Changed("layers")) ||
-		(cmd.Flags().Changed("squash-all") && cmd.Flags().Changed("layers")) ||
 		(cmd.Flags().Changed("squash-all") && cmd.Flags().Changed("squash")) {
-		return errors.New("cannot specify --squash, --squash-all and --layers options together")
+		return errors.New("cannot specify --squash with --layers and --squash-all with --squash")
 	}
 
 	if cmd.Flag("output").Changed && registry.IsRemote() {
@@ -418,7 +417,13 @@ func buildFlagsWrapperToOptions(c *cobra.Command, contextDir string, flags *buil
 	// Squash-all invoked, squash both new and old layers into one.
 	if c.Flags().Changed("squash-all") {
 		flags.Squash = true
-		flags.Layers = false
+		if !c.Flags().Changed("layers") {
+			// Buildah  supports using layers and --squash togather
+			// after https://github.com/containers/buildah/pull/3674
+			// so podman must honor if user wants to still use layers
+			//  with --squash-all.
+			flags.Layers = false
+		}
 	}
 
 	var stdin io.Reader

test/e2e/build_test.go

@@ -178,6 +178,32 @@ var _ = Describe("Podman build", func() {
 		Expect(session).Should(Exit(0))
 	})
 
+	It("podman build verify explicit cache use with squash-all and --layers", func() {
+		session := podmanTest.Podman([]string{"build", "--pull-never", "-f", "build/squash/Dockerfile.squash-c", "--squash-all", "--layers", "-t", "test-squash-d:latest", "build/squash"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+
+		session = podmanTest.Podman([]string{"inspect", "--format", "{{.RootFS.Layers}}", "test-squash-d"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		// Check for one layers
+		Expect(strings.Fields(session.OutputToString())).To(HaveLen(1))
+
+		// Second build must use last squashed build from cache
+		session = podmanTest.Podman([]string{"build", "--pull-never", "-f", "build/squash/Dockerfile.squash-c", "--squash-all", "--layers", "-t", "test", "build/squash"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		// Test if entire build is used from cache
+		Expect(session.OutputToString()).To(ContainSubstring("Using cache"))
+
+		session = podmanTest.Podman([]string{"inspect", "--format", "{{.RootFS.Layers}}", "test-squash-d"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		// Check for one layers
+		Expect(strings.Fields(session.OutputToString())).To(HaveLen(1))
+
+	})
+
 	It("podman build Containerfile locations", func() {
 		// Given
 		// Switch to temp dir and restore it afterwards