go parse 源码
golang parse 代码
文件路径：/src/text/template/parse/parse.go
// Copyright 2011 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 parse builds parse trees for templates as defined by text/template
// and html/template. Clients should use those packages to construct templates
// rather than this one, which provides shared internal data structures not
// intended for general use.
package parse
import (
"bytes"
"fmt"
"runtime"
"strconv"
"strings"
)
// Tree is the representation of a single parsed template.
type Tree struct {
Name string // name of the template represented by the tree.
ParseName string // name of the top-level template during parsing, for error messages.
Root *ListNode // top-level root of the tree.
Mode Mode // parsing mode.
text string // text parsed to create the template (or its parent)
// Parsing only; cleared after parse.
funcs []map[string]any
lex *lexer
token [3]item // three-token lookahead for parser.
peekCount int
vars []string // variables defined at the moment.
treeSet map[string]*Tree
actionLine int // line of left delim starting action
rangeDepth int
}
// A mode value is a set of flags (or 0). Modes control parser behavior.
type Mode uint
const (
ParseComments Mode = 1 << iota // parse comments and add them to AST
SkipFuncCheck // do not check that functions are defined
)
// Copy returns a copy of the Tree. Any parsing state is discarded.
func (t *Tree) Copy() *Tree {
if t == nil {
return nil
}
return &Tree{
Name: t.Name,
ParseName: t.ParseName,
Root: t.Root.CopyList(),
text: t.text,
}
}
// Parse returns a map from template name to parse.Tree, created by parsing the
// templates described in the argument string. The top-level template will be
// given the specified name. If an error is encountered, parsing stops and an
// empty map is returned with the error.
func Parse(name, text, leftDelim, rightDelim string, funcs ...map[string]any) (map[string]*Tree, error) {
treeSet := make(map[string]*Tree)
t := New(name)
t.text = text
_, err := t.Parse(text, leftDelim, rightDelim, treeSet, funcs...)
return treeSet, err
}
// next returns the next token.
func (t *Tree) next() item {
if t.peekCount > 0 {
t.peekCount--
} else {
t.token[0] = t.lex.nextItem()
}
return t.token[t.peekCount]
}
// backup backs the input stream up one token.
func (t *Tree) backup() {
t.peekCount++
}
// backup2 backs the input stream up two tokens.
// The zeroth token is already there.
func (t *Tree) backup2(t1 item) {
t.token[1] = t1
t.peekCount = 2
}
// backup3 backs the input stream up three tokens
// The zeroth token is already there.
func (t *Tree) backup3(t2, t1 item) { // Reverse order: we're pushing back.
t.token[1] = t1
t.token[2] = t2
t.peekCount = 3
}
// peek returns but does not consume the next token.
func (t *Tree) peek() item {
if t.peekCount > 0 {
return t.token[t.peekCount-1]
}
t.peekCount = 1
t.token[0] = t.lex.nextItem()
return t.token[0]
}
// nextNonSpace returns the next non-space token.
func (t *Tree) nextNonSpace() (token item) {
for {
token = t.next()
if token.typ != itemSpace {
break
}
}
return token
}
// peekNonSpace returns but does not consume the next non-space token.
func (t *Tree) peekNonSpace() item {
token := t.nextNonSpace()
t.backup()
return token
}
// Parsing.
// New allocates a new parse tree with the given name.
func New(name string, funcs ...map[string]any) *Tree {
return &Tree{
Name: name,
funcs: funcs,
}
}
// ErrorContext returns a textual representation of the location of the node in the input text.
// The receiver is only used when the node does not have a pointer to the tree inside,
// which can occur in old code.
func (t *Tree) ErrorContext(n Node) (location, context string) {
pos := int(n.Position())
tree := n.tree()
if tree == nil {
tree = t
}
text := tree.text[:pos]
byteNum := strings.LastIndex(text, "\n")
if byteNum == -1 {
byteNum = pos // On first line.
} else {
byteNum++ // After the newline.
byteNum = pos - byteNum
}
lineNum := 1 + strings.Count(text, "\n")
context = n.String()
return fmt.Sprintf("%s:%d:%d", tree.ParseName, lineNum, byteNum), context
}
// errorf formats the error and terminates processing.
func (t *Tree) errorf(format string, args ...any) {
t.Root = nil
format = fmt.Sprintf("template: %s:%d: %s", t.ParseName, t.token[0].line, format)
panic(fmt.Errorf(format, args...))
}
// error terminates processing.
func (t *Tree) error(err error) {
t.errorf("%s", err)
}
// expect consumes the next token and guarantees it has the required type.
func (t *Tree) expect(expected itemType, context string) item {
token := t.nextNonSpace()
if token.typ != expected {
t.unexpected(token, context)
}
return token
}
// expectOneOf consumes the next token and guarantees it has one of the required types.
func (t *Tree) expectOneOf(expected1, expected2 itemType, context string) item {
token := t.nextNonSpace()
if token.typ != expected1 && token.typ != expected2 {
t.unexpected(token, context)
}
return token
}
// unexpected complains about the token and terminates processing.
func (t *Tree) unexpected(token item, context string) {
if token.typ == itemError {
extra := ""
if t.actionLine != 0 && t.actionLine != token.line {
extra = fmt.Sprintf(" in action started at %s:%d", t.ParseName, t.actionLine)
if strings.HasSuffix(token.val, " action") {
extra = extra[len(" in action"):] // avoid "action in action"
}
}
t.errorf("%s%s", token, extra)
}
t.errorf("unexpected %s in %s", token, context)
}
// recover is the handler that turns panics into returns from the top level of Parse.
func (t *Tree) recover(errp *error) {
e := recover()
if e != nil {
if _, ok := e.(runtime.Error); ok {
panic(e)
}
if t != nil {
t.lex.drain()
t.stopParse()
}
*errp = e.(error)
}
}
// startParse initializes the parser, using the lexer.
func (t *Tree) startParse(funcs []map[string]any, lex *lexer, treeSet map[string]*Tree) {
t.Root = nil
t.lex = lex
t.vars = []string{"$"}
t.funcs = funcs
t.treeSet = treeSet
}
// stopParse terminates parsing.
func (t *Tree) stopParse() {
t.lex = nil
t.vars = nil
t.funcs = nil
t.treeSet = nil
}
// Parse parses the template definition string to construct a representation of
// the template for execution. If either action delimiter string is empty, the
// default ("{{" or "}}") is used. Embedded template definitions are added to
// the treeSet map.
func (t *Tree) Parse(text, leftDelim, rightDelim string, treeSet map[string]*Tree, funcs ...map[string]any) (tree *Tree, err error) {
defer t.recover(&err)
t.ParseName = t.Name
emitComment := t.Mode&ParseComments != 0
breakOK := !t.hasFunction("break")
continueOK := !t.hasFunction("continue")
lexer := lex(t.Name, text, leftDelim, rightDelim, emitComment, breakOK, continueOK)
t.startParse(funcs, lexer, treeSet)
t.text = text
t.parse()
t.add()
t.stopParse()
return t, nil
}
// add adds tree to t.treeSet.
func (t *Tree) add() {
tree := t.treeSet[t.Name]
if tree == nil || IsEmptyTree(tree.Root) {
t.treeSet[t.Name] = t
return
}
if !IsEmptyTree(t.Root) {
t.errorf("template: multiple definition of template %q", t.Name)
}
}
// IsEmptyTree reports whether this tree (node) is empty of everything but space or comments.
func IsEmptyTree(n Node) bool {
switch n := n.(type) {
case nil:
return true
case *ActionNode:
case *CommentNode:
return true
case *IfNode:
case *ListNode:
for _, node := range n.Nodes {
if !IsEmptyTree(node) {
return false
}
}
return true
case *RangeNode:
case *TemplateNode:
case *TextNode:
return len(bytes.TrimSpace(n.Text)) == 0
case *WithNode:
default:
panic("unknown node: " + n.String())
}
return false
}
// parse is the top-level parser for a template, essentially the same
// as itemList except it also parses {{define}} actions.
// It runs to EOF.
func (t *Tree) parse() {
t.Root = t.newList(t.peek().pos)
for t.peek().typ != itemEOF {
if t.peek().typ == itemLeftDelim {
delim := t.next()
if t.nextNonSpace().typ == itemDefine {
newT := New("definition") // name will be updated once we know it.
newT.text = t.text
newT.Mode = t.Mode
newT.ParseName = t.ParseName
newT.startParse(t.funcs, t.lex, t.treeSet)
newT.parseDefinition()
continue
}
t.backup2(delim)
}
switch n := t.textOrAction(); n.Type() {
case nodeEnd, nodeElse:
t.errorf("unexpected %s", n)
default:
t.Root.append(n)
}
}
}
// parseDefinition parses a {{define}} ... {{end}} template definition and
// installs the definition in t.treeSet. The "define" keyword has already
// been scanned.
func (t *Tree) parseDefinition() {
const context = "define clause"
name := t.expectOneOf(itemString, itemRawString, context)
var err error
t.Name, err = strconv.Unquote(name.val)
if err != nil {
t.error(err)
}
t.expect(itemRightDelim, context)
var end Node
t.Root, end = t.itemList()
if end.Type() != nodeEnd {
t.errorf("unexpected %s in %s", end, context)
}
t.add()
t.stopParse()
}
// itemList:
//
// textOrAction*
//
// Terminates at {{end}} or {{else}}, returned separately.
func (t *Tree) itemList() (list *ListNode, next Node) {
list = t.newList(t.peekNonSpace().pos)
for t.peekNonSpace().typ != itemEOF {
n := t.textOrAction()
switch n.Type() {
case nodeEnd, nodeElse:
return list, n
}
list.append(n)
}
t.errorf("unexpected EOF")
return
}
// textOrAction:
//
// text | comment | action
func (t *Tree) textOrAction() Node {
switch token := t.nextNonSpace(); token.typ {
case itemText:
return t.newText(token.pos, token.val)
case itemLeftDelim:
t.actionLine = token.line
defer t.clearActionLine()
return t.action()
case itemComment:
return t.newComment(token.pos, token.val)
default:
t.unexpected(token, "input")
}
return nil
}
func (t *Tree) clearActionLine() {
t.actionLine = 0
}
// Action:
//
// control
// command ("|" command)*
//
// Left delim is past. Now get actions.
// First word could be a keyword such as range.
func (t *Tree) action() (n Node) {
switch token := t.nextNonSpace(); token.typ {
case itemBlock:
return t.blockControl()
case itemBreak:
return t.breakControl(token.pos, token.line)
case itemContinue:
return t.continueControl(token.pos, token.line)
case itemElse:
return t.elseControl()
case itemEnd:
return t.endControl()
case itemIf:
return t.ifControl()
case itemRange:
return t.rangeControl()
case itemTemplate:
return t.templateControl()
case itemWith:
return t.withControl()
}
t.backup()
token := t.peek()
// Do not pop variables; they persist until "end".
return t.newAction(token.pos, token.line, t.pipeline("command", itemRightDelim))
}
// Break:
//
// {{break}}
//
// Break keyword is past.
func (t *Tree) breakControl(pos Pos, line int) Node {
if token := t.nextNonSpace(); token.typ != itemRightDelim {
t.unexpected(token, "{{break}}")
}
if t.rangeDepth == 0 {
t.errorf("{{break}} outside {{range}}")
}
return t.newBreak(pos, line)
}
// Continue:
//
// {{continue}}
//
// Continue keyword is past.
func (t *Tree) continueControl(pos Pos, line int) Node {
if token := t.nextNonSpace(); token.typ != itemRightDelim {
t.unexpected(token, "{{continue}}")
}
if t.rangeDepth == 0 {
t.errorf("{{continue}} outside {{range}}")
}
return t.newContinue(pos, line)
}
// Pipeline:
//
// declarations? command ('|' command)*
func (t *Tree) pipeline(context string, end itemType) (pipe *PipeNode) {
token := t.peekNonSpace()
pipe = t.newPipeline(token.pos, token.line, nil)
// Are there declarations or assignments?
decls:
if v := t.peekNonSpace(); v.typ == itemVariable {
t.next()
// Since space is a token, we need 3-token look-ahead here in the worst case:
// in "$x foo" we need to read "foo" (as opposed to ":=") to know that $x is an
// argument variable rather than a declaration. So remember the token
// adjacent to the variable so we can push it back if necessary.
tokenAfterVariable := t.peek()
next := t.peekNonSpace()
switch {
case next.typ == itemAssign, next.typ == itemDeclare:
pipe.IsAssign = next.typ == itemAssign
t.nextNonSpace()
pipe.Decl = append(pipe.Decl, t.newVariable(v.pos, v.val))
t.vars = append(t.vars, v.val)
case next.typ == itemChar && next.val == ",":
t.nextNonSpace()
pipe.Decl = append(pipe.Decl, t.newVariable(v.pos, v.val))
t.vars = append(t.vars, v.val)
if context == "range" && len(pipe.Decl) < 2 {
switch t.peekNonSpace().typ {
case itemVariable, itemRightDelim, itemRightParen:
// second initialized variable in a range pipeline
goto decls
default:
t.errorf("range can only initialize variables")
}
}
t.errorf("too many declarations in %s", context)
case tokenAfterVariable.typ == itemSpace:
t.backup3(v, tokenAfterVariable)
default:
t.backup2(v)
}
}
for {
switch token := t.nextNonSpace(); token.typ {
case end:
// At this point, the pipeline is complete
t.checkPipeline(pipe, context)
return
case itemBool, itemCharConstant, itemComplex, itemDot, itemField, itemIdentifier,
itemNumber, itemNil, itemRawString, itemString, itemVariable, itemLeftParen:
t.backup()
pipe.append(t.command())
default:
t.unexpected(token, context)
}
}
}
func (t *Tree) checkPipeline(pipe *PipeNode, context string) {
// Reject empty pipelines
if len(pipe.Cmds) == 0 {
t.errorf("missing value for %s", context)
}
// Only the first command of a pipeline can start with a non executable operand
for i, c := range pipe.Cmds[1:] {
switch c.Args[0].Type() {
case NodeBool, NodeDot, NodeNil, NodeNumber, NodeString:
// With A|B|C, pipeline stage 2 is B
t.errorf("non executable command in pipeline stage %d", i+2)
}
}
}
func (t *Tree) parseControl(allowElseIf bool, context string) (pos Pos, line int, pipe *PipeNode, list, elseList *ListNode) {
defer t.popVars(len(t.vars))
pipe = t.pipeline(context, itemRightDelim)
if context == "range" {
t.rangeDepth++
}
var next Node
list, next = t.itemList()
if context == "range" {
t.rangeDepth--
}
switch next.Type() {
case nodeEnd: //done
case nodeElse:
if allowElseIf {
// Special case for "else if". If the "else" is followed immediately by an "if",
// the elseControl will have left the "if" token pending. Treat
// {{if a}}_{{else if b}}_{{end}}
// as
// {{if a}}_{{else}}{{if b}}_{{end}}{{end}}.
// To do this, parse the if as usual and stop at it {{end}}; the subsequent{{end}}
// is assumed. This technique works even for long if-else-if chains.
// TODO: Should we allow else-if in with and range?
if t.peek().typ == itemIf {
t.next() // Consume the "if" token.
elseList = t.newList(next.Position())
elseList.append(t.ifControl())
// Do not consume the next item - only one {{end}} required.
break
}
}
elseList, next = t.itemList()
if next.Type() != nodeEnd {
t.errorf("expected end; found %s", next)
}
}
return pipe.Position(), pipe.Line, pipe, list, elseList
}
// If:
//
// {{if pipeline}} itemList {{end}}
// {{if pipeline}} itemList {{else}} itemList {{end}}
//
// If keyword is past.
func (t *Tree) ifControl() Node {
return t.newIf(t.parseControl(true, "if"))
}
// Range:
//
// {{range pipeline}} itemList {{end}}
// {{range pipeline}} itemList {{else}} itemList {{end}}
//
// Range keyword is past.
func (t *Tree) rangeControl() Node {
r := t.newRange(t.parseControl(false, "range"))
return r
}
// With:
//
// {{with pipeline}} itemList {{end}}
// {{with pipeline}} itemList {{else}} itemList {{end}}
//
// If keyword is past.
func (t *Tree) withControl() Node {
return t.newWith(t.parseControl(false, "with"))
}
// End:
//
// {{end}}
//
// End keyword is past.
func (t *Tree) endControl() Node {
return t.newEnd(t.expect(itemRightDelim, "end").pos)
}
// Else:
//
// {{else}}
//
// Else keyword is past.
func (t *Tree) elseControl() Node {
// Special case for "else if".
peek := t.peekNonSpace()
if peek.typ == itemIf {
// We see "{{else if ... " but in effect rewrite it to {{else}}{{if ... ".
return t.newElse(peek.pos, peek.line)
}
token := t.expect(itemRightDelim, "else")
return t.newElse(token.pos, token.line)
}
// Block:
//
// {{block stringValue pipeline}}
//
// Block keyword is past.
// The name must be something that can evaluate to a string.
// The pipeline is mandatory.
func (t *Tree) blockControl() Node {
const context = "block clause"
token := t.nextNonSpace()
name := t.parseTemplateName(token, context)
pipe := t.pipeline(context, itemRightDelim)
block := New(name) // name will be updated once we know it.
block.text = t.text
block.Mode = t.Mode
block.ParseName = t.ParseName
block.startParse(t.funcs, t.lex, t.treeSet)
var end Node
block.Root, end = block.itemList()
if end.Type() != nodeEnd {
t.errorf("unexpected %s in %s", end, context)
}
block.add()
block.stopParse()
return t.newTemplate(token.pos, token.line, name, pipe)
}
// Template:
//
// {{template stringValue pipeline}}
//
// Template keyword is past. The name must be something that can evaluate
// to a string.
func (t *Tree) templateControl() Node {
const context = "template clause"
token := t.nextNonSpace()
name := t.parseTemplateName(token, context)
var pipe *PipeNode
if t.nextNonSpace().typ != itemRightDelim {
t.backup()
// Do not pop variables; they persist until "end".
pipe = t.pipeline(context, itemRightDelim)
}
return t.newTemplate(token.pos, token.line, name, pipe)
}
func (t *Tree) parseTemplateName(token item, context string) (name string) {
switch token.typ {
case itemString, itemRawString:
s, err := strconv.Unquote(token.val)
if err != nil {
t.error(err)
}
name = s
default:
t.unexpected(token, context)
}
return
}
// command:
//
// operand (space operand)*
//
// space-separated arguments up to a pipeline character or right delimiter.
// we consume the pipe character but leave the right delim to terminate the action.
func (t *Tree) command() *CommandNode {
cmd := t.newCommand(t.peekNonSpace().pos)
for {
t.peekNonSpace() // skip leading spaces.
operand := t.operand()
if operand != nil {
cmd.append(operand)
}
switch token := t.next(); token.typ {
case itemSpace:
continue
case itemRightDelim, itemRightParen:
t.backup()
case itemPipe:
// nothing here; break loop below
default:
t.unexpected(token, "operand")
}
break
}
if len(cmd.Args) == 0 {
t.errorf("empty command")
}
return cmd
}
// operand:
//
// term .Field*
//
// An operand is a space-separated component of a command,
// a term possibly followed by field accesses.
// A nil return means the next item is not an operand.
func (t *Tree) operand() Node {
node := t.term()
if node == nil {
return nil
}
if t.peek().typ == itemField {
chain := t.newChain(t.peek().pos, node)
for t.peek().typ == itemField {
chain.Add(t.next().val)
}
// Compatibility with original API: If the term is of type NodeField
// or NodeVariable, just put more fields on the original.
// Otherwise, keep the Chain node.
// Obvious parsing errors involving literal values are detected here.
// More complex error cases will have to be handled at execution time.
switch node.Type() {
case NodeField:
node = t.newField(chain.Position(), chain.String())
case NodeVariable:
node = t.newVariable(chain.Position(), chain.String())
case NodeBool, NodeString, NodeNumber, NodeNil, NodeDot:
t.errorf("unexpected . after term %q", node.String())
default:
node = chain
}
}
return node
}
// term:
//
// literal (number, string, nil, boolean)
// function (identifier)
// .
// .Field
// $
// '(' pipeline ')'
//
// A term is a simple "expression".
// A nil return means the next item is not a term.
func (t *Tree) term() Node {
switch token := t.nextNonSpace(); token.typ {
case itemIdentifier:
checkFunc := t.Mode&SkipFuncCheck == 0
if checkFunc && !t.hasFunction(token.val) {
t.errorf("function %q not defined", token.val)
}
return NewIdentifier(token.val).SetTree(t).SetPos(token.pos)
case itemDot:
return t.newDot(token.pos)
case itemNil:
return t.newNil(token.pos)
case itemVariable:
return t.useVar(token.pos, token.val)
case itemField:
return t.newField(token.pos, token.val)
case itemBool:
return t.newBool(token.pos, token.val == "true")
case itemCharConstant, itemComplex, itemNumber:
number, err := t.newNumber(token.pos, token.val, token.typ)
if err != nil {
t.error(err)
}
return number
case itemLeftParen:
return t.pipeline("parenthesized pipeline", itemRightParen)
case itemString, itemRawString:
s, err := strconv.Unquote(token.val)
if err != nil {
t.error(err)
}
return t.newString(token.pos, token.val, s)
}
t.backup()
return nil
}
// hasFunction reports if a function name exists in the Tree's maps.
func (t *Tree) hasFunction(name string) bool {
for _, funcMap := range t.funcs {
if funcMap == nil {
continue
}
if funcMap[name] != nil {
return true
}
}
return false
}
// popVars trims the variable list to the specified length
func (t *Tree) popVars(n int) {
t.vars = t.vars[:n]
}
// useVar returns a node for a variable reference. It errors if the
// variable is not defined.
func (t *Tree) useVar(pos Pos, name string) Node {
v := t.newVariable(pos, name)
for _, varName := range t.vars {
if varName == v.Ident[0] {
return v
}
}
t.errorf("undefined variable %q", v.Ident[0])
return nil
}
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