bib: propagate error messages from policy.Check()

The errors returned by policy.Check() can contain a reason for why a
path was rejected, especially when the rejection is not based on the
path policy itself.  For example, a non-absolute or non-canonical path
will be rejected.  This information is useful for the user, so let's not
discard that extra information and return all error messages we
encountered.

Co-authored-by: Michael Vogt <[email protected]>

bib/cmd/bootc-image-builder/image.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	cryptorand "crypto/rand"
+	"errors"
 	"fmt"
 	"math"
 	"math/big"
@@ -114,17 +115,19 @@ var (
 )
 
 func checkMountpoints(filesystems []blueprint.FilesystemCustomization, policy *pathpolicy.PathTrie) error {
-	invalid := make([]string, 0)
+	errs := []error{}
 	for _, fs := range filesystems {
 		if err := policy.Check(fs.Mountpoint); err != nil {
-			invalid = append(invalid, fs.Mountpoint)
+			errs = append(errs, err)
 		}
 		if fs.Mountpoint == "/var" {
-			invalid = append(invalid, "/var")
+			// this error message is consistent with the errors returned by policy.Check()
+			// TODO: remove trailing space inside the quoted path when the function is fixed in osbuild/images.
+			errs = append(errs, fmt.Errorf("path '/var ' is not allowed"))
 		}
 	}
-	if len(invalid) > 0 {
-		return fmt.Errorf("The following custom mountpoints are not supported %+q", invalid)
+	if len(errs) > 0 {
+		return fmt.Errorf("The following errors occurred while validating custom mountpoints:\n%w", errors.Join(errs...))
 	}
 	return nil
 }

bib/cmd/bootc-image-builder/image_test.go

@@ -105,23 +105,40 @@ func TestCheckFilesystemCustomizationsValidates(t *testing.T) {
 				{Mountpoint: "/ostree"},
 			},
 			ptmode:      disk.RawPartitioningMode,
-			expectedErr: `The following custom mountpoints are not supported ["/ostree"]`,
+			expectedErr: "The following errors occurred while validating custom mountpoints:\npath '/ostree ' is not allowed",
 		},
 		{
 			fsCust: []blueprint.FilesystemCustomization{
 				{Mountpoint: "/"},
 				{Mountpoint: "/var"},
 			},
 			ptmode:      disk.RawPartitioningMode,
-			expectedErr: `The following custom mountpoints are not supported ["/var"]`,
+			expectedErr: "The following errors occurred while validating custom mountpoints:\npath '/var ' is not allowed",
 		},
 		{
 			fsCust: []blueprint.FilesystemCustomization{
 				{Mountpoint: "/"},
 				{Mountpoint: "/var/data"},
 			},
 			ptmode:      disk.BtrfsPartitioningMode,
-			expectedErr: `The following custom mountpoints are not supported ["/var/data"]`,
+			expectedErr: "The following errors occurred while validating custom mountpoints:\npath '/var/data ' is not allowed",
+		},
+		{
+			fsCust: []blueprint.FilesystemCustomization{
+				{Mountpoint: "/"},
+				{Mountpoint: "/boot/"},
+			},
+			ptmode:      disk.BtrfsPartitioningMode,
+			expectedErr: "The following errors occurred while validating custom mountpoints:\npath must be canonical",
+		},
+		{
+			fsCust: []blueprint.FilesystemCustomization{
+				{Mountpoint: "/"},
+				{Mountpoint: "/boot/"},
+				{Mountpoint: "/opt"},
+			},
+			ptmode:      disk.BtrfsPartitioningMode,
+			expectedErr: "The following errors occurred while validating custom mountpoints:\npath must be canonical\npath '/opt ' is not allowed",
 		},
 	} {
 		cust := &blueprint.Customizations{