reflection: WIP

Signed-off-by: Alejandro Mery <amery@jpi.io>

README.md

@@ -1 +1,78 @@
 # asciigoat's core library
+
+[![Go Reference][godoc-badge]][godoc]
+[![Go Report Card][goreport-badge]][goreport]
+
+This package contains the basics for writing simple parsers of
+text languages heavily inspired by
+[Rob Pike](https://en.wikipedia.org/wiki/Rob_Pike)'s talk on
+[Lexical Scanning in Go](https://go.dev/talks/2011/lex.slide#1) in 2011 which
+you can [watch online](https://www.youtube.com/watch?v=HxaD_trXwRE) to get
+better understanding of the ideas behind **asciigoat**.
+
+**asciigoat** is [MIT](https://opensource.org/license/mit/) licensed.
+
+[godoc]: https://pkg.go.dev/asciigoat.org/core
+[godoc-badge]: https://pkg.go.dev/badge/asciigoat.org/core.svg
+[goreport]: https://goreportcard.com/report/asciigoat.org/core
+[goreport-badge]: https://goreportcard.com/badge/asciigoat.org/core
+
+[godoc-lexer-reader]: https://pkg.go.dev/asciigoat.org/core/lexer#Reader
+[godoc-readcloser]: https://pkg.go.dev/asciigoat.org/core#ReadCloser
+
+## Lexer
+
+### lexer.Reader
+
+The lexer package provides [`lexer.Reader`][godoc-lexer-reader] which is
+actually an [`io.RuneScanner`](https://pkg.go.dev/io#RuneScanner)
+that buffers accepted runes until you are ready to
+[emit](https://pkg.go.dev/asciigoat.org/core/lexer#Reader.Emit) or
+[discard](https://pkg.go.dev/asciigoat.org/core/lexer#Reader.Discard).
+
+### lexer.Position
+
+[`lexer.Position`](https://pkg.go.dev/asciigoat.org/core/lexer#Position)
+is a `(Line, Column)` pair with methods to facilitate tracking
+your position on the source [Reader](https://pkg.go.dev/io#Reader).
+
+### lexer.Error
+
+[`lexer.Error`](https://pkg.go.dev/asciigoat.org/core/lexer#Error)
+is an [unwrappable](https://pkg.go.dev/errors#Unwrap) error with a
+token position and hint attached.
+
+### lexer.StateFn
+
+At the heart of **asciigoat** we have _state functions_ as proposed on [Rob Pike's famous talk](https://www.youtube.com/watch?v=HxaD_trXwRE) which return the next _state function_ parsing is done.
+Additionally there is a [`Run()`](https://pkg.go.dev/asciigoat.org/lexer#Run) helper that implements the loop.
+
+### rune checkers
+
+_Rune checkers_ are simple functions that tell if a rune is of a class or it's not.
+Fundamental checkers are provided by the [`unicode` package](https://pkg.go.dev/unicode).
+
+Our [`lexer.Reader`][godoc-lexer-reader] uses them on its `Accept()` and `AcceptAll()` methods to
+make it easier to consume the _source_ document.
+
+To facilitate the declaration of _rune classes_ in the context of **asciigoat** powered parsers we include
+a series of rune checker factories.
+
+* `NewIsIn(string)`
+* `NewIsInRunes(...rune)`
+* `NewIsNot(checker)`
+* `NewIsOneOf(...checker)`
+
+## Others
+
+### ReadCloser
+
+[ReadCloser][godoc-readcloser] assists in providing a
+[io.Closer](https://pkg.go.dev/io#Closer) to Readers or buffers without on,
+or unearthing one if available so
+[io.ReadCloser](https://pkg.go.dev/io#ReadCloser) can be fulfilled.
+
+## See also
+
+* [asciigoat.org/ini](https://asciigoat.org/ini)
+* [oss.jpi.io](https://oss.jpi.io)

go.mod

@@ -2,20 +2,22 @@ module asciigoat.org/core
 
 go 1.19
 
-require github.com/mgechev/revive v1.3.3
+require (
+	github.com/fatih/structtag v1.2.0
+	github.com/mgechev/revive v1.3.3
+	github.com/pkg/errors v0.9.1
+)
 
 require (
 	github.com/BurntSushi/toml v1.3.2 // indirect
 	github.com/chavacava/garif v0.0.0-20230608123814-4bd63c2919ab // indirect
 	github.com/fatih/color v1.15.0 // indirect
-	github.com/fatih/structtag v1.2.0 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.17 // indirect
 	github.com/mattn/go-runewidth v0.0.9 // indirect
 	github.com/mgechev/dots v0.0.0-20210922191527-e955255bf517 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
 	github.com/olekukonko/tablewriter v0.0.5 // indirect
-	github.com/pkg/errors v0.9.1 // indirect
 	golang.org/x/sys v0.11.0 // indirect
 	golang.org/x/tools v0.12.0 // indirect
 )

lexer/error.go

@@ -25,17 +25,29 @@ type Error struct {
 	Column   int
 
 	Content string
+	Hint    string
 	Err     error
 }
 
+func (err Error) prefix() string {
+	switch {
+	case err.Line > 0 || err.Column > 0:
+		if err.Filename != "" {
+			return fmt.Sprintf("%s:%v:%v", err.Filename, err.Line, err.Column)
+		}
+
+		return fmt.Sprintf("%v:%v", err.Line, err.Column)
+	default:
+		return err.Filename
+	}
+}
+
 func (err Error) Error() string {
 	var s []string
 
-	switch {
-	case err.Line > 0 || err.Column > 0:
-		s = append(s, fmt.Sprintf("%s:%v:%v", err.Filename, err.Line, err.Column))
-	case err.Filename != "":
-		s = append(s, err.Filename)
+	prefix := err.prefix()
+	if prefix != "" {
+		s = append(s, prefix)
 	}
 
 	if err.Err != nil {
@@ -46,6 +58,10 @@ func (err Error) Error() string {
 		s = append(s, fmt.Sprintf("%q", err.Content))
 	}
 
+	if err.Hint != "" {
+		s = append(s, err.Hint)
+	}
+
 	return strings.Join(s, ": ")
 }
 

lexer/runes.go

@@ -21,6 +21,12 @@ func NewIsIn(s string) func(rune) bool {
 	}
 }
 
+// NewIsInRunes generates a rune condition checker that accepts
+// the runes specified
+func NewIsInRunes(s ...rune) func(rune) bool {
+	return NewIsIn(string(s))
+}
+
 // NewIsOneOf generates a run condition checker that accepts runes
 // accepted by any of the given checkers
 func NewIsOneOf(s ...func(rune) bool) func(rune) bool {

reflection/error.go

@@ -0,0 +1,69 @@
+package reflection
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+)
+
+// An InvalidUnmarshalError describes an invalid argument passed to New.
+// (It must be a non-nil pointer.)
+type InvalidUnmarshalError struct {
+	Method string
+	Prefix string
+
+	reflect.Type
+}
+
+func (e *InvalidUnmarshalError) Error() string {
+	var buf bytes.Buffer
+
+	if e.Prefix != "" {
+		_, _ = fmt.Fprintf(&buf, "%s: ", e.Prefix)
+	}
+
+	method := e.Method
+	if method == "" {
+		method = "New"
+	}
+
+	_, _ = fmt.Fprintf(&buf, "%s(", method)
+
+	switch {
+	case e.Type == nil:
+		_, _ = buf.WriteString("nil")
+	case e.Type.Kind() != reflect.Pointer:
+		_, _ = fmt.Fprintf(&buf, "%s %s", "non-pointer", e.Type.String())
+	default:
+		_, _ = fmt.Fprintf(&buf, "%s %s", "nil", e.Type.String())
+	}
+
+	_, _ = buf.WriteString(")")
+
+	return buf.String()
+}
+
+// An UnmarshalTypeError tells something went wrong while processing
+// a type.
+type UnmarshalTypeError struct {
+	Prefix string
+	Err    error
+
+	reflect.Type
+}
+
+func (e UnmarshalTypeError) Unwrap() error {
+	return e.Err
+}
+
+func (e UnmarshalTypeError) Error() string {
+	var buf bytes.Buffer
+
+	if e.Prefix != "" {
+		_, _ = fmt.Fprintf(&buf, "%s: ", e.Prefix)
+	}
+
+	_, _ = fmt.Fprintf(&buf, "%s: %s", e.Type.String(), e.Err)
+
+	return buf.String()
+}

reflection/reflect_help.go

@@ -0,0 +1,16 @@
+package reflection
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func structFieldName(sf reflect.StructField) string {
+	if sf.Anonymous {
+		idx := sf.Index[len(sf.Index)-1]
+
+		return fmt.Sprintf("%s-%v", "anonymous", idx)
+	}
+
+	return sf.Name
+}

reflection/reflection.go

@@ -0,0 +1,40 @@
+// Package reflection helps Marshalling/Unmarshalling data to structs
+package reflection
+
+import (
+	"reflect"
+)
+
+// Reflection provides Marshalling/Unmarshalling oriented view
+// of a value
+type Reflection struct {
+	v reflect.Value
+
+	types map[reflect.Type]TypeInfo
+}
+
+// Value returns the object it reflects
+func (r *Reflection) Value() any {
+	return r.v.Interface()
+}
+
+// New creates a Reflection of the given pointer
+func New(v any) (*Reflection, error) {
+	rv := reflect.ValueOf(v)
+
+	if rv.Kind() != reflect.Pointer || rv.IsNil() {
+		err := &InvalidUnmarshalError{Type: rv.Type()}
+		return nil, err
+	}
+
+	r := &Reflection{
+		v:     rv,
+		types: make(map[reflect.Type]TypeInfo),
+	}
+
+	if err := r.scan(); err != nil {
+		return nil, err
+	}
+
+	return r, nil
+}

reflection/scan.go

@@ -0,0 +1,37 @@
+package reflection
+
+import (
+	"reflect"
+)
+
+func (r *Reflection) scanType(rt reflect.Type) error {
+	switch rt.Kind() {
+	case reflect.Pointer, reflect.Slice:
+		rt = rt.Elem()
+	}
+
+	if _, ok := r.types[rt]; ok {
+		// cached
+		return nil
+	}
+
+	ti, err := NewTypeInfo(rt)
+	if err != nil {
+		return &UnmarshalTypeError{Type: rt, Err: err}
+	}
+
+	r.types[rt] = ti
+
+	for i := range ti.fields {
+		err := r.scanType(ti.fields[i].sf.Type)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (r *Reflection) scan() error {
+	return r.scanType(r.v.Type())
+}

reflection/typeinfo.go

@@ -0,0 +1,108 @@
+package reflection
+
+import (
+	"log"
+	"reflect"
+
+	"github.com/fatih/structtag"
+	"github.com/pkg/errors"
+)
+
+// TypeInfo ...
+type TypeInfo struct {
+	rt reflect.Type
+
+	fields []TypeInfoField
+}
+
+// Type ...
+func (ti *TypeInfo) Type() reflect.Type {
+	return ti.rt
+}
+
+// Kind ...
+func (ti *TypeInfo) Kind() reflect.Kind {
+	return ti.rt.Kind()
+}
+
+// TypeInfoField ...
+type TypeInfoField struct {
+	sf   reflect.StructField
+	tags *structtag.Tags
+
+	Name string
+}
+
+// Type ...
+func (tif *TypeInfoField) Type() reflect.Type {
+	return tif.sf.Type
+}
+
+// Kind ...
+func (tif *TypeInfoField) Kind() reflect.Kind {
+	return tif.sf.Type.Kind()
+}
+
+// Tag ...
+func (tif *TypeInfoField) Tag(key string) (*structtag.Tag, bool) {
+	if tif.tags != nil {
+		tag, _ := tif.tags.Get(key)
+		if tag != nil {
+			return tag, true
+		}
+	}
+	return nil, false
+}
+
+// NewTypeInfo ...
+func NewTypeInfo(rt reflect.Type) (TypeInfo, error) {
+	log.Printf("%s.%s: %s (%s)", "reflection", "NewTypeInfo", rt, rt.Kind())
+
+	ti := TypeInfo{
+		rt: rt,
+	}
+
+	err := ti.init()
+	return ti, err
+}
+
+func (ti *TypeInfo) init() error {
+	switch ti.Kind() {
+	case reflect.Struct:
+		return ti.initStruct()
+	default:
+		return nil
+	}
+}
+
+func (ti *TypeInfo) initStruct() error {
+	// load fields
+	n := ti.rt.NumField()
+	fields := make([]TypeInfoField, 0, n)
+	for i := 0; i < n; i++ {
+		sf := ti.rt.Field(i)
+		tags, err := structtag.Parse(string(sf.Tag))
+
+		if err != nil {
+			// tag parse error
+			err = &UnmarshalTypeError{
+				Type: ti.rt,
+				Err:  errors.Wrap(err, structFieldName(sf)),
+			}
+			return err
+		}
+
+		if sf.IsExported() {
+			log.Printf("%s.%s:   [%v]: %q %s (%s)",
+				"reflection", "NewTypeInfo",
+				i, structFieldName(sf), sf.Type, sf.Type.Kind())
+
+			fields = append(fields, TypeInfoField{
+				sf:   sf,
+				tags: tags,
+			})
+		}
+	}
+	ti.fields = fields
+	return nil
+}