Add container-storage support for Podman and Buildah (#5368)

* feat: add containers-storage support for Podman and Buildah, update tests and documentation

Signed-off-by: Bruce Clark <bruce.clark@mandg.com>

* test: update containers-storage tests to validate package.json and handle missing images

Signed-off-by: Bruce Clark <bruce.clark@mandg.com>

* test: fix rootless containers-storage test setup

Install uidmap for Podman and Buildah CI jobs.
Align temporary rootful and rootless storage paths.
Clean up rootless stores within the builder's user namespace.

Signed-off-by: Bruce Clark <bruce.clark@mandg.com>

* fix: only use containers-storage when explicitly requested

- containers-storage is no longer part of automatic image resolution; it's used only for `--from containers-storage`, the `containers-storage:` scheme, or `default-pull-source: containers-storage` (now an accepted value). Opening a store runs full graph driver init (mounts, locks, store writes), which is too invasive as a probe on every plain image reference.
- rootless stores must be read from inside the builder's user namespace (`podman unshare syft ...`), documented in the README.
- the `containers_image_openpgp` tag is now applied to unit/integration tests and lint, so dev tooling compiles the same provider that ships.
- containers-storage CI runs through `make containers-storage-test` and covers both vfs and overlay stores.

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* fix: exclude cgo btrfs driver and unmount overlay store in cleanup

- cgo-enabled linux builds (`-race` tests, lint) compile go.podman.io's btrfs graph driver, which needs libbtrfs headers. Add `exclude_graphdriver_btrfs` alongside `containers_image_openpgp` everywhere the tag is set; release builds are `CGO_ENABLED=0` and never included it.
- the overlay driver bind-mounts its graphroot inside the rootless user namespace, so the containers-storage test unmounts it before removing the store, and cleanup no longer fails the run.

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Bruce Clark <bruce.clark@mandg.com>
Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>
Co-authored-by: Bruce Clark <bruce.clark@mandg.com>
Co-authored-by: Alex Goodman <wagoodman@users.noreply.github.com>

.make/main.go

@@ -16,6 +16,12 @@ import (
 	"github.com/anchore/go-make/tasks/gotest"
 )
 
+// buildTags must match the linux build in .goreleaser.yaml so tests and lint compile the same code that ships
+// (containers_image_openpgp compiles in stereoscope's real containers-storage provider instead of its stub).
+// exclude_graphdriver_btrfs drops the cgo-only btrfs driver, which needs libbtrfs headers whenever cgo is on (e.g.
+// under -race); release builds are CGO_ENABLED=0 and never include it anyway.
+const buildTags = "containers_image_openpgp,exclude_graphdriver_btrfs"
+
 func main() {
 	Makefile(
 		// shared anchore tasks
@@ -29,6 +35,7 @@ func main() {
 			gotest.Name("unit"),
 			gotest.ExcludeGlob("**/test/**"),
 			gotest.CoverageThreshold(62),
+			gotest.Tags(buildTags),
 			race(),
 		),
 
@@ -52,7 +59,7 @@ func main() {
 					raceFlag = " -race"
 				}
 				Run(
-					"go test -count=1 -timeout=30m"+raceFlag+" ./cmd/syft/internal/test/integration/...",
+					"go test -count=1 -timeout=30m -tags="+buildTags+raceFlag+" ./cmd/syft/internal/test/integration/...",
 					run.Env("GODEBUG", "dontfreezetheworld=1"),
 				)
 			},
@@ -66,7 +73,7 @@ func main() {
 					Log("race detector disabled (RACE=false); skipping race smoke")
 					return
 				}
-				Run("go run -race cmd/syft/main.go anchore/test_images:grype-quality-dotnet-69f15d2")
+				Run("go run -race -tags="+buildTags+" cmd/syft/main.go anchore/test_images:grype-quality-dotnet-69f15d2")
 			},
 		},
 
@@ -96,6 +103,24 @@ func main() {
 			},
 		},
 
+		// containers-storage tests: build a fixture image with BUILDER (podman or buildah) into an isolated local store
+		// and scan it with the snapshot binary. Linux only, and not hooked into "test" since it needs the builder installed.
+		Task{
+			Name:        "containers-storage-test",
+			Description: "Run containers-storage tests (BUILDER=podman|buildah)",
+			Run: func() {
+				bin := snapshotBinPath()
+				if !file.Exists(bin) {
+					Log("snapshot binary not found at %s; building single-target snapshot", bin)
+					Run("make snapshot:single-target")
+				}
+				Run(
+					"bash test/containers-storage/source-test.sh "+config.Env("BUILDER", "podman"),
+					run.Env("SYFT_BINARY_LOCATION", bin),
+				)
+			},
+		},
+
 		// default validation pipeline (replaces Taskfile `default`/`pr-validations`/`validations`).
 		Task{
 			Name:         "default",