html/template: support parsing complex JS template literals

[gostls13.git] / src / html / template / context.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 template

import (
        "fmt"
        "text/template/parse"
)

// context describes the state an HTML parser must be in when it reaches the
// portion of HTML produced by evaluating a particular template node.
//
// The zero value of type context is the start context for a template that
// produces an HTML fragment as defined at
// https://www.w3.org/TR/html5/syntax.html#the-end
// where the context element is null.
type context struct {
        state           state
        delim           delim
        urlPart         urlPart
        jsCtx           jsCtx
        jsTmplExprDepth int
        jsBraceDepth    int
        attr            attr
        element         element
        n               parse.Node // for range break/continue
        err             *Error
}

func (c context) String() string {
        var err error
        if c.err != nil {
                err = c.err
        }
        return fmt.Sprintf("{%v %v %v %v %v %v %v}", c.state, c.delim, c.urlPart, c.jsCtx, c.attr, c.element, err)
}

// eq reports whether two contexts are equal.
func (c context) eq(d context) bool {
        return c.state == d.state &&
                c.delim == d.delim &&
                c.urlPart == d.urlPart &&
                c.jsCtx == d.jsCtx &&
                c.attr == d.attr &&
                c.element == d.element &&
                c.err == d.err
}

// mangle produces an identifier that includes a suffix that distinguishes it
// from template names mangled with different contexts.
func (c context) mangle(templateName string) string {
        // The mangled name for the default context is the input templateName.
        if c.state == stateText {
                return templateName
        }
        s := templateName + "$htmltemplate_" + c.state.String()
        if c.delim != delimNone {
                s += "_" + c.delim.String()
        }
        if c.urlPart != urlPartNone {
                s += "_" + c.urlPart.String()
        }
        if c.jsCtx != jsCtxRegexp {
                s += "_" + c.jsCtx.String()
        }
        if c.attr != attrNone {
                s += "_" + c.attr.String()
        }
        if c.element != elementNone {
                s += "_" + c.element.String()
        }
        return s
}

// state describes a high-level HTML parser state.
//
// It bounds the top of the element stack, and by extension the HTML insertion
// mode, but also contains state that does not correspond to anything in the
// HTML5 parsing algorithm because a single token production in the HTML
// grammar may contain embedded actions in a template. For instance, the quoted
// HTML attribute produced by
//
//      <div title="Hello {{.World}}">
//
// is a single token in HTML's grammar but in a template spans several nodes.
type state uint8

//go:generate stringer -type state

const (
        // stateText is parsed character data. An HTML parser is in
        // this state when its parse position is outside an HTML tag,
        // directive, comment, and special element body.
        stateText state = iota
        // stateTag occurs before an HTML attribute or the end of a tag.
        stateTag
        // stateAttrName occurs inside an attribute name.
        // It occurs between the ^'s in ` ^name^ = value`.
        stateAttrName
        // stateAfterName occurs after an attr name has ended but before any
        // equals sign. It occurs between the ^'s in ` name^ ^= value`.
        stateAfterName
        // stateBeforeValue occurs after the equals sign but before the value.
        // It occurs between the ^'s in ` name =^ ^value`.
        stateBeforeValue
        // stateHTMLCmt occurs inside an <!-- HTML comment -->.
        stateHTMLCmt
        // stateRCDATA occurs inside an RCDATA element (<textarea> or <title>)
        // as described at https://www.w3.org/TR/html5/syntax.html#elements-0
        stateRCDATA
        // stateAttr occurs inside an HTML attribute whose content is text.
        stateAttr
        // stateURL occurs inside an HTML attribute whose content is a URL.
        stateURL
        // stateSrcset occurs inside an HTML srcset attribute.
        stateSrcset
        // stateJS occurs inside an event handler or script element.
        stateJS
        // stateJSDqStr occurs inside a JavaScript double quoted string.
        stateJSDqStr
        // stateJSSqStr occurs inside a JavaScript single quoted string.
        stateJSSqStr
        // stateJSTmplLit occurs inside a JavaScript back quoted string.
        stateJSTmplLit
        // stateJSRegexp occurs inside a JavaScript regexp literal.
        stateJSRegexp
        // stateJSBlockCmt occurs inside a JavaScript /* block comment */.
        stateJSBlockCmt
        // stateJSLineCmt occurs inside a JavaScript // line comment.
        stateJSLineCmt
        // stateJSHTMLOpenCmt occurs inside a JavaScript <!-- HTML-like comment.
        stateJSHTMLOpenCmt
        // stateJSHTMLCloseCmt occurs inside a JavaScript --> HTML-like comment.
        stateJSHTMLCloseCmt
        // stateCSS occurs inside a <style> element or style attribute.
        stateCSS
        // stateCSSDqStr occurs inside a CSS double quoted string.
        stateCSSDqStr
        // stateCSSSqStr occurs inside a CSS single quoted string.
        stateCSSSqStr
        // stateCSSDqURL occurs inside a CSS double quoted url("...").
        stateCSSDqURL
        // stateCSSSqURL occurs inside a CSS single quoted url('...').
        stateCSSSqURL
        // stateCSSURL occurs inside a CSS unquoted url(...).
        stateCSSURL
        // stateCSSBlockCmt occurs inside a CSS /* block comment */.
        stateCSSBlockCmt
        // stateCSSLineCmt occurs inside a CSS // line comment.
        stateCSSLineCmt
        // stateError is an infectious error state outside any valid
        // HTML/CSS/JS construct.
        stateError
        // stateDead marks unreachable code after a {{break}} or {{continue}}.
        stateDead
)

// isComment is true for any state that contains content meant for template
// authors & maintainers, not for end-users or machines.
func isComment(s state) bool {
        switch s {
        case stateHTMLCmt, stateJSBlockCmt, stateJSLineCmt, stateJSHTMLOpenCmt, stateJSHTMLCloseCmt, stateCSSBlockCmt, stateCSSLineCmt:
                return true
        }
        return false
}

// isInTag return whether s occurs solely inside an HTML tag.
func isInTag(s state) bool {
        switch s {
        case stateTag, stateAttrName, stateAfterName, stateBeforeValue, stateAttr:
                return true
        }
        return false
}

// isInScriptLiteral returns true if s is one of the literal states within a
// <script> tag, and as such occurrences of "<!--", "<script", and "</script"
// need to be treated specially.
func isInScriptLiteral(s state) bool {
        // Ignore the comment states (stateJSBlockCmt, stateJSLineCmt,
        // stateJSHTMLOpenCmt, stateJSHTMLCloseCmt) because their content is already
        // omitted from the output.
        switch s {
        case stateJSDqStr, stateJSSqStr, stateJSTmplLit, stateJSRegexp:
                return true
        }
        return false
}

// delim is the delimiter that will end the current HTML attribute.
type delim uint8

//go:generate stringer -type delim

const (
        // delimNone occurs outside any attribute.
        delimNone delim = iota
        // delimDoubleQuote occurs when a double quote (") closes the attribute.
        delimDoubleQuote
        // delimSingleQuote occurs when a single quote (') closes the attribute.
        delimSingleQuote
        // delimSpaceOrTagEnd occurs when a space or right angle bracket (>)
        // closes the attribute.
        delimSpaceOrTagEnd
)

// urlPart identifies a part in an RFC 3986 hierarchical URL to allow different
// encoding strategies.
type urlPart uint8

//go:generate stringer -type urlPart

const (
        // urlPartNone occurs when not in a URL, or possibly at the start:
        // ^ in "^http://auth/path?k=v#frag".
        urlPartNone urlPart = iota
        // urlPartPreQuery occurs in the scheme, authority, or path; between the
        // ^s in "h^ttp://auth/path^?k=v#frag".
        urlPartPreQuery
        // urlPartQueryOrFrag occurs in the query portion between the ^s in
        // "http://auth/path?^k=v#frag^".
        urlPartQueryOrFrag
        // urlPartUnknown occurs due to joining of contexts both before and
        // after the query separator.
        urlPartUnknown
)

// jsCtx determines whether a '/' starts a regular expression literal or a
// division operator.
type jsCtx uint8

//go:generate stringer -type jsCtx

const (
        // jsCtxRegexp occurs where a '/' would start a regexp literal.
        jsCtxRegexp jsCtx = iota
        // jsCtxDivOp occurs where a '/' would start a division operator.
        jsCtxDivOp
        // jsCtxUnknown occurs where a '/' is ambiguous due to context joining.
        jsCtxUnknown
)

// element identifies the HTML element when inside a start tag or special body.
// Certain HTML element (for example <script> and <style>) have bodies that are
// treated differently from stateText so the element type is necessary to
// transition into the correct context at the end of a tag and to identify the
// end delimiter for the body.
type element uint8

//go:generate stringer -type element

const (
        // elementNone occurs outside a special tag or special element body.
        elementNone element = iota
        // elementScript corresponds to the raw text <script> element
        // with JS MIME type or no type attribute.
        elementScript
        // elementStyle corresponds to the raw text <style> element.
        elementStyle
        // elementTextarea corresponds to the RCDATA <textarea> element.
        elementTextarea
        // elementTitle corresponds to the RCDATA <title> element.
        elementTitle
)

//go:generate stringer -type attr

// attr identifies the current HTML attribute when inside the attribute,
// that is, starting from stateAttrName until stateTag/stateText (exclusive).
type attr uint8

const (
        // attrNone corresponds to a normal attribute or no attribute.
        attrNone attr = iota
        // attrScript corresponds to an event handler attribute.
        attrScript
        // attrScriptType corresponds to the type attribute in script HTML element
        attrScriptType
        // attrStyle corresponds to the style attribute whose value is CSS.
        attrStyle
        // attrURL corresponds to an attribute whose value is a URL.
        attrURL
        // attrSrcset corresponds to a srcset attribute.
        attrSrcset
)