build: reuse parse.ContainerIgnoreFile from buildah

podman's logic to parse excludes from `--ignorefile` is not consistent
with buildah, use code directly from imagebuilder.

Closes: https://github.com/containers/podman/issues/25746

Signed-off-by: flouthoc <flouthoc.git@gmail.com>

cmd/podman/common/build.go

@@ -25,6 +25,7 @@ import (
 	"github.com/containers/podman/v5/cmd/podman/utils"
 	"github.com/containers/podman/v5/pkg/domain/entities"
 	"github.com/containers/podman/v5/pkg/env"
+	"github.com/openshift/imagebuilder"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 )
@@ -585,9 +586,9 @@ func buildFlagsWrapperToOptions(c *cobra.Command, contextDir string, flags *Buil
 	}
 
 	if flags.IgnoreFile != "" {
-		excludes, err := parseDockerignore(flags.IgnoreFile)
+		excludes, err := imagebuilder.ParseIgnore(flags.IgnoreFile)
 		if err != nil {
-			return nil, fmt.Errorf("unable to obtain decrypt config: %w", err)
+			return nil, fmt.Errorf("unable to parse ignore file: %w", err)
 		}
 		opts.Excludes = excludes
 	}
@@ -628,21 +629,6 @@ func getDecryptConfig(decryptionKeys []string) (*encconfig.DecryptConfig, error)
 	return decConfig, nil
 }
 
-func parseDockerignore(ignoreFile string) ([]string, error) {
-	excludes := []string{}
-	ignore, err := os.ReadFile(ignoreFile)
-	if err != nil {
-		return excludes, err
-	}
-	for _, e := range strings.Split(string(ignore), "\n") {
-		if len(e) == 0 || e[0] == '#' {
-			continue
-		}
-		excludes = append(excludes, e)
-	}
-	return excludes, nil
-}
-
 func areContainerfilesValid(contextDir string, containerFiles []string) error {
 	for _, f := range containerFiles {
 		if isURL(f) || f == "/dev/stdin" {

test/system/070-build.bats

@@ -584,6 +584,7 @@ Labels.\"io.buildah.version\" | $buildah_version
          -subdir2/sub2 -subdir2/sub2.txt
          -subdir2/sub3 -subdir2/sub3.txt
          this-file-does-not-match-anything-in-ignore-file
+         -foo
          comment
     )
     for f in "${files[@]}"; do
@@ -613,6 +614,7 @@ subdir1
 subdir2
 !*/sub1*
 !subdir1/sub3*
+/foo
 EOF
 
         # Build an image. For .dockerignore