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-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-/* Package datafmt implements syntax-directed, type-driven formatting
- of arbitrary data structures. Formatting a data structure consists of
- two phases: first, a parser reads a format specification and builds a
- "compiled" format. Then, the format can be applied repeatedly to
- arbitrary values. Applying a format to a value evaluates to a []byte
- containing the formatted value bytes, or nil.
-
- A format specification is a set of package declarations and format rules:
-
- Format = [ Entry { ";" Entry } [ ";" ] ] .
- Entry = PackageDecl | FormatRule .
-
- (The syntax of a format specification is presented in the same EBNF
- notation as used in the Go language specification. The syntax of white
- space, comments, identifiers, and string literals is the same as in Go.)
-
- A package declaration binds a package name (such as 'ast') to a
- package import path (such as '"go/ast"'). Each package used (in
- a type name, see below) must be declared once before use.
-
- PackageDecl = PackageName ImportPath .
- PackageName = identifier .
- ImportPath = string .
-
- A format rule binds a rule name to a format expression. A rule name
- may be a type name or one of the special names 'default' or '/'.
- A type name may be the name of a predeclared type (for example, 'int',
- 'float32', etc.), the package-qualified name of a user-defined type
- (for example, 'ast.MapType'), or an identifier indicating the structure
- of unnamed composite types ('array', 'chan', 'func', 'interface', 'map',
- or 'ptr'). Each rule must have a unique name; rules can be declared in
- any order.
-
- FormatRule = RuleName "=" Expression .
- RuleName = TypeName | "default" | "/" .
- TypeName = [ PackageName "." ] identifier .
-
- To format a value, the value's type name is used to select the format rule
- (there is an override mechanism, see below). The format expression of the
- selected rule specifies how the value is formatted. Each format expression,
- when applied to a value, evaluates to a byte sequence or nil.
-
- In its most general form, a format expression is a list of alternatives,
- each of which is a sequence of operands:
-
- Expression = [ Sequence ] { "|" [ Sequence ] } .
- Sequence = Operand { Operand } .
-
- The formatted result produced by an expression is the result of the first
- alternative sequence that evaluates to a non-nil result; if there is no
- such alternative, the expression evaluates to nil. The result produced by
- an operand sequence is the concatenation of the results of its operands.
- If any operand in the sequence evaluates to nil, the entire sequence
- evaluates to nil.
-
- There are five kinds of operands:
-
- Operand = Literal | Field | Group | Option | Repetition .
-
- Literals evaluate to themselves, with two substitutions. First,
- %-formats expand in the manner of fmt.Printf, with the current value
- passed as the parameter. Second, the current indentation (see below)
- is inserted after every newline or form feed character.
-
- Literal = string .
-
- This table shows string literals applied to the value 42 and the
- corresponding formatted result:
-
- "foo" foo
- "%x" 2a
- "x = %d" x = 42
- "%#x = %d" 0x2a = 42
-
- A field operand is a field name optionally followed by an alternate
- rule name. The field name may be an identifier or one of the special
- names @ or *.
-
- Field = FieldName [ ":" RuleName ] .
- FieldName = identifier | "@" | "*" .
-
- If the field name is an identifier, the current value must be a struct,
- and there must be a field with that name in the struct. The same lookup
- rules apply as in the Go language (for instance, the name of an anonymous
- field is the unqualified type name). The field name denotes the field
- value in the struct. If the field is not found, formatting is aborted
- and an error message is returned. (TODO consider changing the semantics
- such that if a field is not found, it evaluates to nil).
-
- The special name '@' denotes the current value.
-
- The meaning of the special name '*' depends on the type of the current
- value:
-
- array, slice types array, slice element (inside {} only, see below)
- interfaces value stored in interface
- pointers value pointed to by pointer
-
- (Implementation restriction: channel, function and map types are not
- supported due to missing reflection support).
-
- Fields are evaluated as follows: If the field value is nil, or an array
- or slice element does not exist, the result is nil (see below for details
- on array/slice elements). If the value is not nil the field value is
- formatted (recursively) using the rule corresponding to its type name,
- or the alternate rule name, if given.
-
- The following example shows a complete format specification for a
- struct 'myPackage.Point'. Assume the package
-
- package myPackage // in directory myDir/myPackage
- type Point struct {
- name string;
- x, y int;
- }
-
- Applying the format specification
-
- myPackage "myDir/myPackage";
- int = "%d";
- hexInt = "0x%x";
- string = "---%s---";
- myPackage.Point = name "{" x ", " y:hexInt "}";
-
- to the value myPackage.Point{"foo", 3, 15} results in
-
- ---foo---{3, 0xf}
-
- Finally, an operand may be a grouped, optional, or repeated expression.
- A grouped expression ("group") groups a more complex expression (body)
- so that it can be used in place of a single operand:
-
- Group = "(" [ Indentation ">>" ] Body ")" .
- Indentation = Expression .
- Body = Expression .
-
- A group body may be prefixed by an indentation expression followed by '>>'.
- The indentation expression is applied to the current value like any other
- expression and the result, if not nil, is appended to the current indentation
- during the evaluation of the body (see also formatting state, below).
-
- An optional expression ("option") is enclosed in '[]' brackets.
-
- Option = "[" Body "]" .
-
- An option evaluates to its body, except that if the body evaluates to nil,
- the option expression evaluates to an empty []byte. Thus an option's purpose
- is to protect the expression containing the option from a nil operand.
-
- A repeated expression ("repetition") is enclosed in '{}' braces.
-
- Repetition = "{" Body [ "/" Separator ] "}" .
- Separator = Expression .
-
- A repeated expression is evaluated as follows: The body is evaluated
- repeatedly and its results are concatenated until the body evaluates
- to nil. The result of the repetition is the (possibly empty) concatenation,
- but it is never nil. An implicit index is supplied for the evaluation of
- the body: that index is used to address elements of arrays or slices. If
- the corresponding elements do not exist, the field denoting the element
- evaluates to nil (which in turn may terminate the repetition).
-
- The body of a repetition may be followed by a '/' and a "separator"
- expression. If the separator is present, it is invoked between repetitions
- of the body.
-
- The following example shows a complete format specification for formatting
- a slice of unnamed type. Applying the specification
-
- int = "%b";
- array = { * / ", " }; // array is the type name for an unnamed slice
-
- to the value '[]int{2, 3, 5, 7}' results in
-
- 10, 11, 101, 111
-
- Default rule: If a format rule named 'default' is present, it is used for
- formatting a value if no other rule was found. A common default rule is
-
- default = "%v"
-
- to provide default formatting for basic types without having to specify
- a specific rule for each basic type.
-
- Global separator rule: If a format rule named '/' is present, it is
- invoked with the current value between literals. If the separator
- expression evaluates to nil, it is ignored.
-
- For instance, a global separator rule may be used to punctuate a sequence
- of values with commas. The rules:
-
- default = "%v";
- / = ", ";
-
- will format an argument list by printing each one in its default format,
- separated by a comma and a space.
-*/
-package datafmt
-
-import (
- "bytes"
- "fmt"
- "go/token"
- "io"
- "os"
- "reflect"
- "runtime"
-)
-
-
-// ----------------------------------------------------------------------------
-// Format representation
-
-// Custom formatters implement the Formatter function type.
-// A formatter is invoked with the current formatting state, the
-// value to format, and the rule name under which the formatter
-// was installed (the same formatter function may be installed
-// under different names). The formatter may access the current state
-// to guide formatting and use State.Write to append to the state's
-// output.
-//
-// A formatter must return a boolean value indicating if it evaluated
-// to a non-nil value (true), or a nil value (false).
-//
-type Formatter func(state *State, value interface{}, ruleName string) bool
-
-
-// A FormatterMap is a set of custom formatters.
-// It maps a rule name to a formatter function.
-//
-type FormatterMap map[string]Formatter
-
-
-// A parsed format expression is built from the following nodes.
-//
-type (
- expr interface{}
-
- alternatives []expr // x | y | z
-
- sequence []expr // x y z
-
- literal [][]byte // a list of string segments, possibly starting with '%'
-
- field struct {
- fieldName string // including "@", "*"
- ruleName string // "" if no rule name specified
- }
-
- group struct {
- indent, body expr // (indent >> body)
- }
-
- option struct {
- body expr // [body]
- }
-
- repetition struct {
- body, separator expr // {body / separator}
- }
-
- custom struct {
- ruleName string
- fun Formatter
- }
-)
-
-
-// A Format is the result of parsing a format specification.
-// The format may be applied repeatedly to format values.
-//
-type Format map[string]expr
-
-
-// ----------------------------------------------------------------------------
-// Formatting
-
-// An application-specific environment may be provided to Format.Apply;
-// the environment is available inside custom formatters via State.Env().
-// Environments must implement copying; the Copy method must return an
-// complete copy of the receiver. This is necessary so that the formatter
-// can save and restore an environment (in case of an absent expression).
-//
-// If the Environment doesn't change during formatting (this is under
-// control of the custom formatters), the Copy function can simply return
-// the receiver, and thus can be very light-weight.
-//
-type Environment interface {
- Copy() Environment
-}
-
-
-// State represents the current formatting state.
-// It is provided as argument to custom formatters.
-//
-type State struct {
- fmt Format // format in use
- env Environment // user-supplied environment
- errors chan os.Error // not chan *Error (errors <- nil would be wrong!)
- hasOutput bool // true after the first literal has been written
- indent bytes.Buffer // current indentation
- output bytes.Buffer // format output
- linePos token.Position // position of line beginning (Column == 0)
- default_ expr // possibly nil
- separator expr // possibly nil
-}
-
-
-func newState(fmt Format, env Environment, errors chan os.Error) *State {
- s := new(State)
- s.fmt = fmt
- s.env = env
- s.errors = errors
- s.linePos = token.Position{Line: 1}
-
- // if we have a default rule, cache it's expression for fast access
- if x, found := fmt["default"]; found {
- s.default_ = x
- }
-
- // if we have a global separator rule, cache it's expression for fast access
- if x, found := fmt["/"]; found {
- s.separator = x
- }
-
- return s
-}
-
-
-// Env returns the environment passed to Format.Apply.
-func (s *State) Env() interface{} { return s.env }
-
-
-// LinePos returns the position of the current line beginning
-// in the state's output buffer. Line numbers start at 1.
-//
-func (s *State) LinePos() token.Position { return s.linePos }
-
-
-// Pos returns the position of the next byte to be written to the
-// output buffer. Line numbers start at 1.
-//
-func (s *State) Pos() token.Position {
- offs := s.output.Len()
- return token.Position{Line: s.linePos.Line, Column: offs - s.linePos.Offset, Offset: offs}
-}
-
-
-// Write writes data to the output buffer, inserting the indentation
-// string after each newline or form feed character. It cannot return an error.
-//
-func (s *State) Write(data []byte) (int, os.Error) {
- n := 0
- i0 := 0
- for i, ch := range data {
- if ch == '\n' || ch == '\f' {
- // write text segment and indentation
- n1, _ := s.output.Write(data[i0 : i+1])
- n2, _ := s.output.Write(s.indent.Bytes())
- n += n1 + n2
- i0 = i + 1
- s.linePos.Offset = s.output.Len()
- s.linePos.Line++
- }
- }
- n3, _ := s.output.Write(data[i0:])
- return n + n3, nil
-}
-
-
-type checkpoint struct {
- env Environment
- hasOutput bool
- outputLen int
- linePos token.Position
-}
-
-
-func (s *State) save() checkpoint {
- saved := checkpoint{nil, s.hasOutput, s.output.Len(), s.linePos}
- if s.env != nil {
- saved.env = s.env.Copy()
- }
- return saved
-}
-
-
-func (s *State) restore(m checkpoint) {
- s.env = m.env
- s.output.Truncate(m.outputLen)
-}
-
-
-func (s *State) error(msg string) {
- s.errors <- os.NewError(msg)
- runtime.Goexit()
-}
-
-
-// TODO At the moment, unnamed types are simply mapped to the default
-// names below. For instance, all unnamed arrays are mapped to
-// 'array' which is not really sufficient. Eventually one may want
-// to be able to specify rules for say an unnamed slice of T.
-//
-
-func typename(typ reflect.Type) string {
- switch typ.Kind() {
- case reflect.Array:
- return "array"
- case reflect.Slice:
- return "array"
- case reflect.Chan:
- return "chan"
- case reflect.Func:
- return "func"
- case reflect.Interface:
- return "interface"
- case reflect.Map:
- return "map"
- case reflect.Ptr:
- return "ptr"
- }
- return typ.String()
-}
-
-func (s *State) getFormat(name string) expr {
- if fexpr, found := s.fmt[name]; found {
- return fexpr
- }
-
- if s.default_ != nil {
- return s.default_
- }
-
- s.error(fmt.Sprintf("no format rule for type: '%s'", name))
- return nil
-}
-
-
-// eval applies a format expression fexpr to a value. If the expression
-// evaluates internally to a non-nil []byte, that slice is appended to
-// the state's output buffer and eval returns true. Otherwise, eval
-// returns false and the state remains unchanged.
-//
-func (s *State) eval(fexpr expr, value reflect.Value, index int) bool {
- // an empty format expression always evaluates
- // to a non-nil (but empty) []byte
- if fexpr == nil {
- return true
- }
-
- switch t := fexpr.(type) {
- case alternatives:
- // append the result of the first alternative that evaluates to
- // a non-nil []byte to the state's output
- mark := s.save()
- for _, x := range t {
- if s.eval(x, value, index) {
- return true
- }
- s.restore(mark)
- }
- return false
-
- case sequence:
- // append the result of all operands to the state's output
- // unless a nil result is encountered
- mark := s.save()
- for _, x := range t {
- if !s.eval(x, value, index) {
- s.restore(mark)
- return false
- }
- }
- return true
-
- case literal:
- // write separator, if any
- if s.hasOutput {
- // not the first literal
- if s.separator != nil {
- sep := s.separator // save current separator
- s.separator = nil // and disable it (avoid recursion)
- mark := s.save()
- if !s.eval(sep, value, index) {
- s.restore(mark)
- }
- s.separator = sep // enable it again
- }
- }
- s.hasOutput = true
- // write literal segments
- for _, lit := range t {
- if len(lit) > 1 && lit[0] == '%' {
- // segment contains a %-format at the beginning
- if lit[1] == '%' {
- // "%%" is printed as a single "%"
- s.Write(lit[1:])
- } else {
- // use s instead of s.output to get indentation right
- fmt.Fprintf(s, string(lit), value.Interface())
- }
- } else {
- // segment contains no %-formats
- s.Write(lit)
- }
- }
- return true // a literal never evaluates to nil
-
- case *field:
- // determine field value
- switch t.fieldName {
- case "@":
- // field value is current value
-
- case "*":
- // indirection: operation is type-specific
- switch v := value; v.Kind() {
- case reflect.Array:
- if v.Len() <= index {
- return false
- }
- value = v.Index(index)
-
- case reflect.Slice:
- if v.IsNil() || v.Len() <= index {
- return false
- }
- value = v.Index(index)
-
- case reflect.Map:
- s.error("reflection support for maps incomplete")
-
- case reflect.Ptr:
- if v.IsNil() {
- return false
- }
- value = v.Elem()
-
- case reflect.Interface:
- if v.IsNil() {
- return false
- }
- value = v.Elem()
-
- case reflect.Chan:
- s.error("reflection support for chans incomplete")
-
- case reflect.Func:
- s.error("reflection support for funcs incomplete")
-
- default:
- s.error(fmt.Sprintf("error: * does not apply to `%s`", value.Type()))
- }
-
- default:
- // value is value of named field
- var field reflect.Value
- if sval := value; sval.Kind() == reflect.Struct {
- field = sval.FieldByName(t.fieldName)
- if !field.IsValid() {
- // TODO consider just returning false in this case
- s.error(fmt.Sprintf("error: no field `%s` in `%s`", t.fieldName, value.Type()))
- }
- }
- value = field
- }
-
- // determine rule
- ruleName := t.ruleName
- if ruleName == "" {
- // no alternate rule name, value type determines rule
- ruleName = typename(value.Type())
- }
- fexpr = s.getFormat(ruleName)
-
- mark := s.save()
- if !s.eval(fexpr, value, index) {
- s.restore(mark)
- return false
- }
- return true
-
- case *group:
- // remember current indentation
- indentLen := s.indent.Len()
-
- // update current indentation
- mark := s.save()
- s.eval(t.indent, value, index)
- // if the indentation evaluates to nil, the state's output buffer
- // didn't change - either way it's ok to append the difference to
- // the current indentation
- s.indent.Write(s.output.Bytes()[mark.outputLen:s.output.Len()])
- s.restore(mark)
-
- // format group body
- mark = s.save()
- b := true
- if !s.eval(t.body, value, index) {
- s.restore(mark)
- b = false
- }
-
- // reset indentation
- s.indent.Truncate(indentLen)
- return b
-
- case *option:
- // evaluate the body and append the result to the state's output
- // buffer unless the result is nil
- mark := s.save()
- if !s.eval(t.body, value, 0) { // TODO is 0 index correct?
- s.restore(mark)
- }
- return true // an option never evaluates to nil
-
- case *repetition:
- // evaluate the body and append the result to the state's output
- // buffer until a result is nil
- for i := 0; ; i++ {
- mark := s.save()
- // write separator, if any
- if i > 0 && t.separator != nil {
- // nil result from separator is ignored
- mark := s.save()
- if !s.eval(t.separator, value, i) {
- s.restore(mark)
- }
- }
- if !s.eval(t.body, value, i) {
- s.restore(mark)
- break
- }
- }
- return true // a repetition never evaluates to nil
-
- case *custom:
- // invoke the custom formatter to obtain the result
- mark := s.save()
- if !t.fun(s, value.Interface(), t.ruleName) {
- s.restore(mark)
- return false
- }
- return true
- }
-
- panic("unreachable")
- return false
-}
-
-
-// Eval formats each argument according to the format
-// f and returns the resulting []byte and os.Error. If
-// an error occurred, the []byte contains the partially
-// formatted result. An environment env may be passed
-// in which is available in custom formatters through
-// the state parameter.
-//
-func (f Format) Eval(env Environment, args ...interface{}) ([]byte, os.Error) {
- if f == nil {
- return nil, os.NewError("format is nil")
- }
-
- errors := make(chan os.Error)
- s := newState(f, env, errors)
-
- go func() {
- for _, v := range args {
- fld := reflect.ValueOf(v)
- if !fld.IsValid() {
- errors <- os.NewError("nil argument")
- return
- }
- mark := s.save()
- if !s.eval(s.getFormat(typename(fld.Type())), fld, 0) { // TODO is 0 index correct?
- s.restore(mark)
- }
- }
- errors <- nil // no errors
- }()
-
- err := <-errors
- return s.output.Bytes(), err
-}
-
-
-// ----------------------------------------------------------------------------
-// Convenience functions
-
-// Fprint formats each argument according to the format f
-// and writes to w. The result is the total number of bytes
-// written and an os.Error, if any.
-//
-func (f Format) Fprint(w io.Writer, env Environment, args ...interface{}) (int, os.Error) {
- data, err := f.Eval(env, args...)
- if err != nil {
- // TODO should we print partial result in case of error?
- return 0, err
- }
- return w.Write(data)
-}
-
-
-// Print formats each argument according to the format f
-// and writes to standard output. The result is the total
-// number of bytes written and an os.Error, if any.
-//
-func (f Format) Print(args ...interface{}) (int, os.Error) {
- return f.Fprint(os.Stdout, nil, args...)
-}
-
-
-// Sprint formats each argument according to the format f
-// and returns the resulting string. If an error occurs
-// during formatting, the result string contains the
-// partially formatted result followed by an error message.
-//
-func (f Format) Sprint(args ...interface{}) string {
- var buf bytes.Buffer
- _, err := f.Fprint(&buf, nil, args...)
- if err != nil {
- var i interface{} = args
- fmt.Fprintf(&buf, "--- Sprint(%s) failed: %v", fmt.Sprint(i), err)
- }
- return buf.String()
-}
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