hcl/zcl/zclsyntax/parser_template.go

package zclsyntax

import (
	"fmt"
	"strings"
	"unicode"

	"github.com/zclconf/go-cty/cty"
	"github.com/zclconf/go-zcl/zcl"
)

func (p *parser) ParseTemplate() (Expression, zcl.Diagnostics) {
	return p.parseTemplate(TokenEOF)
}

func (p *parser) parseTemplate(end TokenType) (Expression, zcl.Diagnostics) {
	exprs, unwrap, rng, diags := p.parseTemplateInner(end)

	return &TemplateExpr{
		Parts:  exprs,
		Unwrap: unwrap,

		SrcRange: rng,
	}, diags
}

func (p *parser) parseTemplateInner(end TokenType) ([]Expression, bool, zcl.Range, zcl.Diagnostics) {
	parts, diags := p.parseTemplateParts(end)
	tp := templateParser{
		Tokens:   parts.Tokens,
		SrcRange: parts.SrcRange,
	}
	exprs, exprsDiags := tp.parseRoot()
	diags = append(diags, exprsDiags...)

	unwrap := false
	if len(parts.Tokens) == 2 { // one real token and one synthetic "end" token
		if _, isInterp := parts.Tokens[0].(*templateInterpToken); isInterp {
			unwrap = true
		}
	}

	return exprs, unwrap, parts.SrcRange, diags
}

type templateParser struct {
	Tokens   []templateToken
	SrcRange zcl.Range

	pos int
}

func (p *templateParser) parseRoot() ([]Expression, zcl.Diagnostics) {
	var exprs []Expression
	var diags zcl.Diagnostics

	for {
		next := p.Peek()
		if _, isEnd := next.(*templateEndToken); isEnd {
			break
		}

		expr, exprDiags := p.parseExpr()
		diags = append(diags, exprDiags...)
		exprs = append(exprs, expr)
	}

	return exprs, diags
}

func (p *templateParser) parseExpr() (Expression, zcl.Diagnostics) {
	next := p.Read()
	switch tok := next.(type) {

	case *templateLiteralToken:
		return &LiteralValueExpr{
			Val:      cty.StringVal(tok.Val),
			SrcRange: tok.SrcRange,
		}, nil

	case *templateInterpToken:
		return tok.Expr, nil

	case *templateIfToken:
		// TODO: implement
		panic("template if token not yet implemented")

	case *templateForToken:
		// TODO: implement
		panic("template for token not yet implemented")

	case *templateEndToken:
		return errPlaceholderExpr(tok.SrcRange), zcl.Diagnostics{
			{
				// This is a particularly unhelpful diagnostic, so callers
				// should attempt to pre-empt it and produce a more helpful
				// diagnostic that is context-aware.
				Severity: zcl.DiagError,
				Summary:  "Unexpected end of template",
				Detail:   "The control directives within this template are unbalanced.",
				Subject:  &tok.SrcRange,
			},
		}

	case *templateEndCtrlToken:
		return errPlaceholderExpr(tok.SrcRange), zcl.Diagnostics{
			{
				Severity: zcl.DiagError,
				Summary:  fmt.Sprintf("Unexpected %s directive", tok.Name()),
				Detail:   "The control directives within this template are unbalanced.",
				Subject:  &tok.SrcRange,
			},
		}

	default:
		// should never happen, because above should be exhaustive
		panic(fmt.Sprintf("unhandled template token type %T", next))
	}
}

func (p *templateParser) Peek() templateToken {
	return p.Tokens[p.pos]
}

func (p *templateParser) Read() templateToken {
	ret := p.Peek()
	if _, end := ret.(*templateEndToken); !end {
		p.pos++
	}
	return ret
}

// parseTemplateParts produces a flat sequence of "template tokens", which are
// either literal values (with any "trimming" already applied), interpolation
// sequences, or control flow markers.
//
// A further pass is required on the result to turn it into an AST.
func (p *parser) parseTemplateParts(end TokenType) (*templateParts, zcl.Diagnostics) {
	var parts []templateToken
	var diags zcl.Diagnostics

	startRange := p.NextRange()
	ltrimNext := false
	nextCanTrimPrev := false
	var endRange zcl.Range

Token:
	for {
		next := p.Read()
		if next.Type == end {
			// all done!
			endRange = next.Range
			break
		}

		ltrim := ltrimNext
		ltrimNext = false
		canTrimPrev := nextCanTrimPrev
		nextCanTrimPrev = false

		switch next.Type {
		case TokenStringLit, TokenQuotedLit:
			str, strDiags := p.decodeStringLit(next)
			diags = append(diags, strDiags...)

			if ltrim {
				str = strings.TrimLeftFunc(str, unicode.IsSpace)
			}

			parts = append(parts, &templateLiteralToken{
				Val:      str,
				SrcRange: next.Range,
			})
			nextCanTrimPrev = true

		case TokenTemplateInterp:
			// if the opener is ${~ then we want to eat any trailing whitespace
			// in the preceding literal token, assuming it is indeed a literal
			// token.
			if canTrimPrev && len(next.Bytes) == 3 && next.Bytes[2] == '~' && len(parts) > 0 {
				prevExpr := parts[len(parts)-1]
				if lexpr, ok := prevExpr.(*templateLiteralToken); ok {
					lexpr.Val = strings.TrimRightFunc(lexpr.Val, unicode.IsSpace)
				}
			}

			p.PushIncludeNewlines(false)
			expr, exprDiags := p.ParseExpression()
			diags = append(diags, exprDiags...)
			close := p.Peek()
			if close.Type != TokenTemplateSeqEnd {
				if !p.recovery {
					diags = append(diags, &zcl.Diagnostic{
						Severity: zcl.DiagError,
						Summary:  "Extra characters after interpolation expression",
						Detail:   "Expected a closing brace to end the interpolation expression, but found extra characters.",
						Subject:  &close.Range,
						Context:  zcl.RangeBetween(startRange, close.Range).Ptr(),
					})
				}
				p.recover(TokenTemplateSeqEnd)
			} else {
				p.Read() // eat closing brace

				// If the closer is ~} then we want to eat any leading
				// whitespace on the next token, if it turns out to be a
				// literal token.
				if len(close.Bytes) == 2 && close.Bytes[0] == '~' {
					ltrimNext = true
				}
			}
			p.PopIncludeNewlines()
			parts = append(parts, &templateInterpToken{
				Expr:     expr,
				SrcRange: zcl.RangeBetween(next.Range, close.Range),
			})
		case TokenTemplateControl:
			panic("template control sequences not yet supported")

		default:
			if !p.recovery {
				diags = append(diags, &zcl.Diagnostic{
					Severity: zcl.DiagError,
					Summary:  "Unterminated template string",
					Detail:   "No closing marker was found for the string.",
					Subject:  &next.Range,
					Context:  zcl.RangeBetween(startRange, next.Range).Ptr(),
				})
			}
			final := p.recover(end)
			endRange = final.Range
			break Token
		}
	}

	if len(parts) == 0 {
		// If a sequence has no content, we'll treat it as if it had an
		// empty string in it because that's what the user probably means
		// if they write "" in configuration.
		parts = append(parts, &templateLiteralToken{
			Val: "",
			SrcRange: zcl.Range{
				// Range is the zero-character span immediately after the
				// opening quote.
				Filename: startRange.Filename,
				Start:    startRange.End,
				End:      startRange.End,
			},
		})
	}

	// Always end with an end token, so the parser can produce diagnostics
	// about unclosed items with proper position information.
	parts = append(parts, &templateEndToken{
		SrcRange: endRange,
	})

	ret := &templateParts{
		Tokens:   parts,
		SrcRange: zcl.RangeBetween(startRange, endRange),
	}

	return ret, diags
}

type templateParts struct {
	Tokens   []templateToken
	SrcRange zcl.Range
}

// templateToken is a higher-level token that represents a single atom within
// the template language. Our template parsing first raises the raw token
// stream to a sequence of templateToken, and then transforms the result into
// an expression tree.
type templateToken interface {
	templateToken() templateToken
}

type templateLiteralToken struct {
	Val      string
	SrcRange zcl.Range
	isTemplateToken
}

type templateInterpToken struct {
	Expr     Expression
	SrcRange zcl.Range
	isTemplateToken
}

type templateIfToken struct {
	CondExpr Expression
	SrcRange zcl.Range
	isTemplateToken
}

type templateForToken struct {
	KeyVar   string // empty if ignoring key
	ValVar   string
	CollExpr Expression
	SrcRange zcl.Range
	isTemplateToken
}

type templateEndCtrlType int

const (
	templateEndIf templateEndCtrlType = iota
	templateElse
	templateEndFor
)

type templateEndCtrlToken struct {
	Type     templateEndCtrlType
	SrcRange zcl.Range
	isTemplateToken
}

func (t *templateEndCtrlToken) Name() string {
	switch t.Type {
	case templateEndIf:
		return "endif"
	case templateElse:
		return "else"
	case templateEndFor:
		return "endfor"
	default:
		// should never happen
		panic("invalid templateEndCtrlType")
	}
}

type templateEndToken struct {
	SrcRange zcl.Range
	isTemplateToken
}

type isTemplateToken [0]int

func (t isTemplateToken) templateToken() templateToken {
	return t
}