frontend/dockerfile/dockerignore: remove hard-coded filename from error

While this function would usually be used for read a `.dockerignore` file,
it accepts a Reader and can also be used to handle ignore patterns from
other files (e.g. `Dockerfile.dockerignore`) or other sources. The error
was also wrapped multiple times in some code-paths, which could lead to
an error being formatted as:

    failed to parse dockerignore: error reading .dockerignore: <some error>

Let's remove mention of the `.dockerignore` filename from the error, and
leave it to the caller to include the filename.

This patch also brings the  MainContext dockerignore error inline with the
NamedContext dockerignore error, now printing the exact name of the file.

Co-authored-by: Justin Chadwell <me@jedevc.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

frontend/dockerfile/dockerignore/dockerignore.go

@@ -6,8 +6,6 @@ import (
 	"io"
 	"path/filepath"
 	"strings"
-
-	"github.com/pkg/errors"
 )
 
 // ReadAll reads an ignore file from a reader and returns the list of file
@@ -69,7 +67,7 @@ func ReadAll(reader io.Reader) ([]string, error) {
 		excludes = append(excludes, pattern)
 	}
 	if err := scanner.Err(); err != nil {
-		return nil, errors.Wrap(err, "error reading .dockerignore")
+		return nil, err
 	}
 	return excludes, nil
 }

frontend/dockerui/config.go

@@ -80,7 +80,8 @@ type Client struct {
 	g           flightcontrol.Group[*buildContext]
 	bopts       client.BuildOpts
 
-	dockerignore []byte
+	dockerignore     []byte
+	dockerignoreName string
 }
 
 type SBOM struct {
@@ -375,6 +376,7 @@ func (bc *Client) ReadEntrypoint(ctx context.Context, lang string, opts ...llb.L
 	})
 	if err == nil {
 		bc.dockerignore = dt
+		bc.dockerignoreName = bctx.filename + ".dockerignore"
 	}
 
 	return &Source{
@@ -435,13 +437,14 @@ func (bc *Client) MainContext(ctx context.Context, opts ...llb.LocalOption) (*ll
 			dt = []byte{}
 		}
 		bc.dockerignore = dt
+		bc.dockerignoreName = DefaultDockerignoreName
 	}
 
 	var excludes []string
 	if len(bc.dockerignore) != 0 {
 		excludes, err = dockerignore.ReadAll(bytes.NewBuffer(bc.dockerignore))
 		if err != nil {
-			return nil, errors.Wrap(err, "failed to parse dockerignore")
+			return nil, errors.Wrapf(err, "failed parsing %s", bc.dockerignoreName)
 		}
 	}
 

frontend/dockerui/namedcontext.go

@@ -208,7 +208,7 @@ func (bc *Client) namedContextRecursive(ctx context.Context, name string, nameWi
 			if len(dt) != 0 {
 				excludes, err = dockerignore.ReadAll(bytes.NewBuffer(dt))
 				if err != nil {
-					return nil, nil, err
+					return nil, nil, errors.Wrapf(err, "failed parsing %s", DefaultDockerignoreName)
 				}
 			}
 		}