⚙️ Add ability to build from Dockerfiles directly

vendor/github.com/asottile/dockerfile/parse.go

@@ -0,0 +1,95 @@
+package dockerfile
+
+import (
+	"io"
+	"os"
+	"sort"
+
+	"github.com/moby/buildkit/frontend/dockerfile/command"
+	"github.com/moby/buildkit/frontend/dockerfile/parser"
+)
+
+// Represents a single line (layer) in a Dockerfile.
+// For example `FROM ubuntu:xenial`
+type Command struct {
+	Cmd       string   // lowercased command name (ex: `from`)
+	SubCmd    string   // for ONBUILD only this holds the sub-command
+	Json      bool     // whether the value is written in json form
+	Original  string   // The original source line
+	StartLine int      // The original source line number which starts this command
+	EndLine   int      // The original source line number which ends this command
+	Flags     []string // Any flags such as `--from=...` for `COPY`.
+	Value     []string // The contents of the command (ex: `ubuntu:xenial`)
+}
+
+// A failure in opening a file for reading.
+type IOError struct {
+	Msg string
+}
+
+func (e IOError) Error() string {
+	return e.Msg
+}
+
+// A failure in parsing the file as a dockerfile.
+type ParseError struct {
+	Msg string
+}
+
+func (e ParseError) Error() string {
+	return e.Msg
+}
+
+// List all legal cmds in a dockerfile
+func AllCmds() []string {
+	var ret []string
+	for k := range command.Commands {
+		ret = append(ret, k)
+	}
+	sort.Strings(ret)
+	return ret
+}
+
+// Parse a Dockerfile from a reader.  A ParseError may occur.
+func ParseReader(file io.Reader) ([]Command, error) {
+	res, err := parser.Parse(file)
+	if err != nil {
+		return nil, ParseError{err.Error()}
+	}
+
+	var ret []Command
+	for _, child := range res.AST.Children {
+		cmd := Command{
+			Cmd:       child.Value,
+			Original:  child.Original,
+			StartLine: child.StartLine,
+			EndLine:   child.EndLine,
+			Flags:     child.Flags,
+		}
+
+		// Only happens for ONBUILD
+		if child.Next != nil && len(child.Next.Children) > 0 {
+			cmd.SubCmd = child.Next.Children[0].Value
+			child = child.Next.Children[0]
+		}
+
+		cmd.Json = child.Attributes["json"]
+		for n := child.Next; n != nil; n = n.Next {
+			cmd.Value = append(cmd.Value, n.Value)
+		}
+
+		ret = append(ret, cmd)
+	}
+	return ret, nil
+}
+
+// Parse a Dockerfile from a filename.  An IOError or ParseError may occur.
+func ParseFile(filename string) ([]Command, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, IOError{err.Error()}
+	}
+	defer file.Close()
+
+	return ParseReader(file)
+}