go-jsonnet/ast/ast.go

/*
Copyright 2016 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package ast provides AST nodes and ancillary structures and algorithms.
package ast

import (
	"fmt"
)

// Identifier represents a variable / parameter / field name.
//+gen set
type Identifier string

// Identifiers represents an Identifier slice.
type Identifiers []Identifier

// TODO(jbeda) implement interning of identifiers if necessary.  The C++
// version does so.

// ---------------------------------------------------------------------------

// Context represents the surrounding context of a node (e.g. a function it's in)
type Context *string

// Node represents a node in the AST.
type Node interface {
	Context() Context
	Loc() *LocationRange
	FreeVariables() Identifiers
	SetFreeVariables(Identifiers)
	SetContext(Context)
}

// Nodes represents a Node slice.
type Nodes []Node

// ---------------------------------------------------------------------------

// NodeBase holds fields common to all node types.
type NodeBase struct {
	LocRange LocationRange
	// This is the fodder that precedes the first token of the node.
	// If the node is left-recursive, i.e. the first token is actually
	// a token of a sub-expression, then Fodder is nil.
	Fodder   Fodder
	Ctx      Context
	FreeVars Identifiers
}

// NewNodeBase creates a new NodeBase from initial LocationRange and
// Identifiers.
func NewNodeBase(loc LocationRange, fodder Fodder, freeVariables Identifiers) NodeBase {
	return NodeBase{
		LocRange: loc,
		Fodder:   fodder,
		FreeVars: freeVariables,
	}
}

// NewNodeBaseLoc creates a new NodeBase from an initial LocationRange.
func NewNodeBaseLoc(loc LocationRange, fodder Fodder) NodeBase {
	return NewNodeBase(loc, fodder, []Identifier{})
}

// Loc returns a NodeBase's loc.
func (n *NodeBase) Loc() *LocationRange {
	return &n.LocRange
}

// OpenFodder returns a NodeBase's opening fodder.
func (n *NodeBase) OpenFodder() Fodder {
	return n.Fodder
}

// FreeVariables returns a NodeBase's freeVariables.
func (n *NodeBase) FreeVariables() Identifiers {
	return n.FreeVars
}

// SetFreeVariables sets a NodeBase's freeVariables.
func (n *NodeBase) SetFreeVariables(idents Identifiers) {
	n.FreeVars = idents
}

// Context returns a NodeBase's context.
func (n *NodeBase) Context() Context {
	return n.Ctx
}

// SetContext sets a NodeBase's context.
func (n *NodeBase) SetContext(context Context) {
	n.Ctx = context
}

// ---------------------------------------------------------------------------

// IfSpec represents an if-specification in a comprehension.
type IfSpec struct {
	IfFodder Fodder
	Expr     Node
}

// ForSpec represents a for-specification in a comprehension.
// Example:
// expr for x in arr1 for y in arr2 for z in arr3
// The order is the same as in python, i.e. the leftmost is the outermost.
//
// Our internal representation reflects how they are semantically nested:
// ForSpec(z, outer=ForSpec(y, outer=ForSpec(x, outer=nil)))
// Any ifspecs are attached to the relevant ForSpec.
//
// Ifs are attached to the one on the left, for example:
// expr for x in arr1 for y in arr2 if x % 2 == 0 for z in arr3
// The if is attached to the y forspec.
//
// It desugares to:
// flatMap(\x ->
//         flatMap(\y ->
//                 flatMap(\z -> [expr], arr3)
//                 arr2)
//         arr3)
type ForSpec struct {
	ForFodder  Fodder
	VarFodder  Fodder
	VarName    Identifier
	InFodder   Fodder
	Expr       Node
	Conditions []IfSpec
	Outer      *ForSpec
}

// ---------------------------------------------------------------------------

// Apply represents a function call
type Apply struct {
	NodeBase
	Target     Node
	FodderLeft Fodder
	Arguments  Arguments
	// Always false if there were no arguments.
	TrailingComma    bool
	TailStrict       bool
	FodderRight      Fodder
	TailStrictFodder Fodder
}

// NamedArgument represents a named argument to function call x=1.
type NamedArgument struct {
	NameFodder  Fodder
	Name        Identifier
	EqFodder    Fodder
	Arg         Node
	CommaFodder Fodder
}

// CommaSeparatedExpr represents an expression that is an element of a
// comma-separated list of expressions (e.g. in an array or the arguments of a
// call)
type CommaSeparatedExpr struct {
	Expr        Node
	CommaFodder Fodder
}

// Arguments represents positional and named arguments to a function call
// f(x, y, z=1).
type Arguments struct {
	Positional []CommaSeparatedExpr
	Named      []NamedArgument
}

// ---------------------------------------------------------------------------

// ApplyBrace represents e { }.  Desugared to e + { }.
type ApplyBrace struct {
	NodeBase
	Left  Node
	Right Node
}

// ---------------------------------------------------------------------------

// Array represents array constructors [1, 2, 3].
type Array struct {
	NodeBase
	Elements []CommaSeparatedExpr
	// Always false if there were no elements.
	TrailingComma bool
	CloseFodder   Fodder
}

// ---------------------------------------------------------------------------

// ArrayComp represents array comprehensions (which are like Python list
// comprehensions)
type ArrayComp struct {
	NodeBase
	Body                Node
	TrailingComma       bool
	TrailingCommaFodder Fodder
	Spec                ForSpec
	CloseFodder         Fodder
}

// ---------------------------------------------------------------------------

// Assert represents an assert expression (not an object-level assert).
//
// After parsing, message can be nil indicating that no message was
// specified. This AST is elimiated by desugaring.
type Assert struct {
	NodeBase
	Cond            Node
	ColonFodder     Fodder
	Message         Node
	SemicolonFodder Fodder
	Rest            Node
}

// ---------------------------------------------------------------------------

// BinaryOp represents a binary operator.
type BinaryOp int

// Binary operators
const (
	BopMult BinaryOp = iota
	BopDiv
	BopPercent

	BopPlus
	BopMinus

	BopShiftL
	BopShiftR

	BopGreater
	BopGreaterEq
	BopLess
	BopLessEq
	BopIn

	BopManifestEqual
	BopManifestUnequal

	BopBitwiseAnd
	BopBitwiseXor
	BopBitwiseOr

	BopAnd
	BopOr
)

var bopStrings = []string{
	BopMult:    "*",
	BopDiv:     "/",
	BopPercent: "%",

	BopPlus:  "+",
	BopMinus: "-",

	BopShiftL: "<<",
	BopShiftR: ">>",

	BopGreater:   ">",
	BopGreaterEq: ">=",
	BopLess:      "<",
	BopLessEq:    "<=",
	BopIn:        "in",

	BopManifestEqual:   "==",
	BopManifestUnequal: "!=",

	BopBitwiseAnd: "&",
	BopBitwiseXor: "^",
	BopBitwiseOr:  "|",

	BopAnd: "&&",
	BopOr:  "||",
}

// BopMap is a map from binary operator token strings to BinaryOp values.
var BopMap = map[string]BinaryOp{
	"*": BopMult,
	"/": BopDiv,
	"%": BopPercent,

	"+": BopPlus,
	"-": BopMinus,

	"<<": BopShiftL,
	">>": BopShiftR,

	">":  BopGreater,
	">=": BopGreaterEq,
	"<":  BopLess,
	"<=": BopLessEq,
	"in": BopIn,

	"==": BopManifestEqual,
	"!=": BopManifestUnequal,

	"&": BopBitwiseAnd,
	"^": BopBitwiseXor,
	"|": BopBitwiseOr,

	"&&": BopAnd,
	"||": BopOr,
}

func (b BinaryOp) String() string {
	if b < 0 || int(b) >= len(bopStrings) {
		panic(fmt.Sprintf("INTERNAL ERROR: Unrecognised binary operator: %d", b))
	}
	return bopStrings[b]
}

// Binary represents binary operators.
type Binary struct {
	NodeBase
	Left     Node
	OpFodder Fodder
	Op       BinaryOp
	Right    Node
}

// ---------------------------------------------------------------------------

// Conditional represents if/then/else.
//
// After parsing, branchFalse can be nil indicating that no else branch
// was specified.  The desugarer fills this in with a LiteralNull
type Conditional struct {
	NodeBase
	Cond        Node
	ThenFodder  Fodder
	BranchTrue  Node
	ElseFodder  Fodder
	BranchFalse Node
}

// ---------------------------------------------------------------------------

// Dollar represents the $ keyword
type Dollar struct{ NodeBase }

// ---------------------------------------------------------------------------

// Error represents the error e.
type Error struct {
	NodeBase
	Expr Node
}

// ---------------------------------------------------------------------------

// Function represents a function definition
type Function struct {
	NodeBase
	ParenLeftFodder Fodder
	Parameters      []Parameter
	// Always false if there were no parameters.
	TrailingComma    bool
	ParenRightFodder Fodder
	Body             Node
}

// Parameter represents a parameter of function.
// If DefaultArg is set, it's an optional named parameter.
// Otherwise, it's a positional parameter and EqFodder is not used.
type Parameter struct {
	NameFodder  Fodder
	Name        Identifier
	EqFodder    Fodder
	DefaultArg  Node
	CommaFodder Fodder
}

// CommaSeparatedID represents an expression that is an element of a
// comma-separated list of identifiers (e.g. an array of parameters)
type CommaSeparatedID struct {
	NameFodder  Fodder
	Name        Identifier
	CommaFodder Fodder
}

// ---------------------------------------------------------------------------

// Import represents import "file".
type Import struct {
	NodeBase
	File *LiteralString
}

// ---------------------------------------------------------------------------

// ImportStr represents importstr "file".
type ImportStr struct {
	NodeBase
	File *LiteralString
}

// ---------------------------------------------------------------------------

// Index represents both e[e] and the syntax sugar e.f.
//
// One of index and id will be nil before desugaring.  After desugaring id
// will be nil.
type Index struct {
	NodeBase
	Target Node
	// When Index is being used, this is the fodder before the '['.
	// When Id is being used, this is the fodder before the '.'.
	LeftBracketFodder Fodder
	Index             Node
	// When Index is being used, this is the fodder before the ']'.
	// When Id is being used, this is always empty.
	RightBracketFodder Fodder
	Id                 *Identifier
}

// Slice represents an array slice a[begin:end:step].
type Slice struct {
	NodeBase
	Target Node

	LeftBracketFodder Fodder
	// Each of these can be nil
	BeginIndex         Node
	EndColonFodder     Fodder
	EndIndex           Node
	StepColonFodder    Fodder
	Step               Node
	RightBracketFodder Fodder
}

// ---------------------------------------------------------------------------

// LocalBind is a helper struct for astLocal
type LocalBind struct {
	VarFodder Fodder
	Variable  Identifier
	EqFodder  Fodder
	// If Fun is set then its body == Body.
	Body Node
	// There is no base fodder in Fun because there was no `function` keyword.
	Fun *Function
	// The fodder before the closing ',' or ';' (whichever it is)
	CloseFodder Fodder
}

// LocalBinds represents a LocalBind slice.
type LocalBinds []LocalBind

// Local represents local x = e; e.  After desugaring, functionSugar is false.
type Local struct {
	NodeBase
	Binds LocalBinds
	Body  Node
}

// ---------------------------------------------------------------------------

// LiteralBoolean represents true and false
type LiteralBoolean struct {
	NodeBase
	Value bool
}

// ---------------------------------------------------------------------------

// LiteralNull represents the null keyword
type LiteralNull struct{ NodeBase }

// ---------------------------------------------------------------------------

// LiteralNumber represents a JSON number
type LiteralNumber struct {
	NodeBase
	OriginalString string
}

// ---------------------------------------------------------------------------

// LiteralStringKind represents the kind of a literal string.
type LiteralStringKind int

// Literal string kinds
const (
	StringSingle LiteralStringKind = iota
	StringDouble
	StringBlock
	VerbatimStringDouble
	VerbatimStringSingle
)

// FullyEscaped returns true iff the literal string kind may contain escape
// sequences that require unescaping.
func (k LiteralStringKind) FullyEscaped() bool {
	switch k {
	case StringSingle, StringDouble:
		return true
	case StringBlock, VerbatimStringDouble, VerbatimStringSingle:
		return false
	}
	panic(fmt.Sprintf("Unknown string kind: %v", k))
}

// LiteralString represents a JSON string
type LiteralString struct {
	NodeBase
	Value       string
	Kind        LiteralStringKind
	BlockIndent string
}

// ---------------------------------------------------------------------------

// ObjectFieldKind represents the kind of an object field.
type ObjectFieldKind int

// Kinds of object fields
const (
	// In the following:
	// <colon> is a short-hand for
	//     <opF> ( ':' | '::' | ':::' | '+:' | '+::' | '+:::' )
	// f1, f2, f3, opF and commaF refer to the various Fodder fields.

	// For brevity, we omit the syntax for method sugar, which applies to all
	// but ObjectAssert below.

	// <f1> 'assert' <expr2> '[' <opF> ':' <expr3> ']' <commaF>
	// where expr3 can be nil
	ObjectAssert ObjectFieldKind = iota
	// <f1> <id> <colon> <expr2> <commaF>
	ObjectFieldID
	// <f1> '[' <expr1> <f2> ']' <colon> <expr2> <commaF>
	ObjectFieldExpr
	// <expr1> <colon> <expr2> <commaF>
	ObjectFieldStr
	// <f1> 'local' <f2> <id> '=' <expr2> <commaF>
	ObjectLocal
)

// ObjectFieldHide represents the visibility of an object field.
type ObjectFieldHide int

// Object field visibilities
const (
	ObjectFieldHidden  ObjectFieldHide = iota // f:: e
	ObjectFieldInherit                        // f: e
	ObjectFieldVisible                        // f::: e
)

// ObjectField represents a field of an object or object comprehension.
// TODO(sbarzowski) consider having separate types for various kinds
type ObjectField struct {
	Kind       ObjectFieldKind
	Hide       ObjectFieldHide // (ignore if kind != astObjectFieldID/Expr/Str)
	SuperSugar bool            // +:  (ignore if kind != astObjectFieldID/Expr/Str)

	// f(x, y, z): ...  (ignore if kind  == astObjectAssert)
	// If Method is set then Expr2 == Method.Body.
	// There is no base fodder in Method because there was no `function`
	// keyword.
	Method       *Function
	Fodder1      Fodder
	Expr1        Node // Not in scope of the object
	Id           *Identifier
	Fodder2      Fodder
	OpFodder     Fodder
	Expr2, Expr3 Node // In scope of the object (can see self).
	CommaFodder  Fodder
}

// ObjectFieldLocalNoMethod creates a non-method local object field.
func ObjectFieldLocalNoMethod(id *Identifier, body Node) ObjectField {
	return ObjectField{
		Kind:  ObjectLocal,
		Hide:  ObjectFieldVisible,
		Id:    id,
		Expr2: body,
	}
}

// ObjectFields represents an ObjectField slice.
type ObjectFields []ObjectField

// Object represents object constructors { f: e ... }.
//
// The trailing comma is only allowed if len(fields) > 0.  Converted to
// DesugaredObject during desugaring.
type Object struct {
	NodeBase
	Fields        ObjectFields
	TrailingComma bool
	CloseFodder   Fodder
}

// ---------------------------------------------------------------------------

// DesugaredObjectField represents a desugared object field.
type DesugaredObjectField struct {
	Hide      ObjectFieldHide
	Name      Node
	Body      Node
	PlusSuper bool
}

// DesugaredObjectFields represents a DesugaredObjectField slice.
type DesugaredObjectFields []DesugaredObjectField

// DesugaredObject represents object constructors { f: e ... } after
// desugaring.
//
// The assertions either return true or raise an error.
type DesugaredObject struct {
	NodeBase
	Asserts Nodes
	Fields  DesugaredObjectFields
	Locals  LocalBinds
}

// ---------------------------------------------------------------------------

// ObjectComp represents object comprehension
//   { [e]: e for x in e for.. if... }.
type ObjectComp struct {
	NodeBase
	Fields        ObjectFields
	TrailingComma bool
	Spec          ForSpec
	CloseFodder   Fodder
}

// ---------------------------------------------------------------------------

// Parens represents parentheses
//   ( e )
type Parens struct {
	NodeBase
	Inner       Node
	CloseFodder Fodder
}

// ---------------------------------------------------------------------------

// Self represents the self keyword.
type Self struct{ NodeBase }

// ---------------------------------------------------------------------------

// SuperIndex represents the super[e] and super.f constructs.
//
// Either index or identifier will be set before desugaring.  After desugaring, id will be
// nil.
type SuperIndex struct {
	NodeBase
	// If super.f, the fodder before the '.'
	// If super[e], the fodder before the '['.
	DotFodder Fodder
	Index     Node
	// If super.f, the fodder before the 'f'
	// If super[e], the fodder before the ']'.
	IDFodder Fodder
	Id       *Identifier
}

// InSuper represents the e in super construct.
type InSuper struct {
	NodeBase
	Index       Node
	InFodder    Fodder
	SuperFodder Fodder
}

// ---------------------------------------------------------------------------

// UnaryOp represents a unary operator.
type UnaryOp int

// Unary operators
const (
	UopNot UnaryOp = iota
	UopBitwiseNot
	UopPlus
	UopMinus
)

var uopStrings = []string{
	UopNot:        "!",
	UopBitwiseNot: "~",
	UopPlus:       "+",
	UopMinus:      "-",
}

// UopMap is a map from unary operator token strings to UnaryOp values.
var UopMap = map[string]UnaryOp{
	"!": UopNot,
	"~": UopBitwiseNot,
	"+": UopPlus,
	"-": UopMinus,
}

func (u UnaryOp) String() string {
	if u < 0 || int(u) >= len(uopStrings) {
		panic(fmt.Sprintf("INTERNAL ERROR: Unrecognised unary operator: %d", u))
	}
	return uopStrings[u]
}

// Unary represents unary operators.
type Unary struct {
	NodeBase
	Op   UnaryOp
	Expr Node
}

// ---------------------------------------------------------------------------

// Var represents variables.
type Var struct {
	NodeBase
	Id Identifier
}

// ---------------------------------------------------------------------------