expression_template.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

package hclsyntax

import (
	"bytes"
	"fmt"

	"github.com/hashicorp/hcl/v2"
	"github.com/zclconf/go-cty/cty"
	"github.com/zclconf/go-cty/cty/convert"
)

type TemplateExpr struct {
	Parts []Expression

	SrcRange hcl.Range
}

func (e *TemplateExpr) walkChildNodes(w internalWalkFunc) {
	for _, part := range e.Parts {
		w(part)
	}
}

func (e *TemplateExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
	buf := &bytes.Buffer{}
	var diags hcl.Diagnostics
	isKnown := true

	// Maintain a set of marks for values used in the template
	marks := make(cty.ValueMarks)

	for _, part := range e.Parts {
		if part == nil {
			// we silently ignore nil parts as they only occur for configuration that is already known to be invalid
			continue
		}

		partVal, partDiags := part.Value(ctx)
		diags = append(diags, partDiags...)

		if partVal.IsNull() {
			diags = append(diags, &hcl.Diagnostic{
				Severity:    hcl.DiagError,
				Summary:     "Invalid template interpolation value",
				Detail:      "The expression result is null. Cannot include a null value in a string template.",
				Subject:     part.Range().Ptr(),
				Context:     &e.SrcRange,
				Expression:  part,
				EvalContext: ctx,
			})
			continue
		}

		// Unmark the part and merge its marks into the set
		unmarkedVal, partMarks := partVal.Unmark()
		for k, v := range partMarks {
			marks[k] = v
		}

		if !partVal.IsKnown() {
			// If any part is unknown then the result as a whole must be
			// unknown too. We'll keep on processing the rest of the parts
			// anyway, because we want to still emit any diagnostics resulting
			// from evaluating those.
			isKnown = false
			continue
		}

		strVal, err := convert.Convert(unmarkedVal, cty.String)
		if err != nil {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid template interpolation value",
				Detail: fmt.Sprintf(
					"Cannot include the given value in a string template: %s.",
					err.Error(),
				),
				Subject:     part.Range().Ptr(),
				Context:     &e.SrcRange,
				Expression:  part,
				EvalContext: ctx,
			})
			continue
		}

		// If we're just continuing to validate after we found an unknown value
		// then we'll skip appending so that "buf" will contain only the
		// known prefix of the result.
		if isKnown && !diags.HasErrors() {
			buf.WriteString(strVal.AsString())
		}
	}

	var ret cty.Value
	if !isKnown {
		ret = cty.UnknownVal(cty.String)
		if !diags.HasErrors() { // Invalid input means our partial result buffer is suspect
			if knownPrefix := buf.String(); knownPrefix != "" {
				byteLen := len(knownPrefix)
				// Impose a reasonable upper limit to avoid producing too long a prefix.
				// The 128 B is about 10% of the safety limits in cty's msgpack decoder.
				// @see https://github.com/zclconf/go-cty/blob/v1.13.2/cty/msgpack/unknown.go#L170-L175
				//
				// This operation is safe because StringPrefix removes incomplete trailing grapheme clusters.
				if byteLen > 128 { // arbitrarily-decided threshold
					byteLen = 128
				}
				ret = ret.Refine().StringPrefix(knownPrefix[:byteLen]).NewValue()
			}
		}
	} else {
		ret = cty.StringVal(buf.String())
	}

	// A template rendering result is never null.
	ret = ret.RefineNotNull()

	// Apply the full set of marks to the returned value
	return ret.WithMarks(marks), diags
}

func (e *TemplateExpr) Range() hcl.Range {
	return e.SrcRange
}

func (e *TemplateExpr) StartRange() hcl.Range {
	return e.Parts[0].StartRange()
}

// IsStringLiteral returns true if and only if the template consists only of
// single string literal, as would be created for a simple quoted string like
// "foo".
//
// If this function returns true, then calling Value on the same expression
// with a nil EvalContext will return the literal value.
//
// Note that "${"foo"}", "${1}", etc aren't considered literal values for the
// purposes of this method, because the intent of this method is to identify
// situations where the user seems to be explicitly intending literal string
// interpretation, not situations that result in literals as a technicality
// of the template expression unwrapping behavior.
func (e *TemplateExpr) IsStringLiteral() bool {
	if len(e.Parts) != 1 {
		return false
	}
	_, ok := e.Parts[0].(*LiteralValueExpr)
	return ok
}

// TemplateJoinExpr is used to convert tuples of strings produced by template
// constructs (i.e. for loops) into flat strings, by converting the values
// tos strings and joining them. This AST node is not used directly; it's
// produced as part of the AST of a "for" loop in a template.
type TemplateJoinExpr struct {
	Tuple Expression
}

func (e *TemplateJoinExpr) walkChildNodes(w internalWalkFunc) {
	w(e.Tuple)
}

func (e *TemplateJoinExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
	tuple, diags := e.Tuple.Value(ctx)

	if tuple.IsNull() {
		// This indicates a bug in the code that constructed the AST.
		panic("TemplateJoinExpr got null tuple")
	}
	if tuple.Type() == cty.DynamicPseudoType {
		return cty.UnknownVal(cty.String), diags
	}
	if !tuple.Type().IsTupleType() {
		// This indicates a bug in the code that constructed the AST.
		panic("TemplateJoinExpr got non-tuple tuple")
	}
	if !tuple.IsKnown() {
		return cty.UnknownVal(cty.String), diags
	}

	tuple, marks := tuple.Unmark()
	allMarks := []cty.ValueMarks{marks}
	buf := &bytes.Buffer{}
	it := tuple.ElementIterator()
	for it.Next() {
		_, val := it.Element()

		if val.IsNull() {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid template interpolation value",
				Detail: fmt.Sprintf(
					"An iteration result is null. Cannot include a null value in a string template.",
				),
				Subject:     e.Range().Ptr(),
				Expression:  e,
				EvalContext: ctx,
			})
			continue
		}
		if val.Type() == cty.DynamicPseudoType {
			return cty.UnknownVal(cty.String).WithMarks(marks), diags
		}
		strVal, err := convert.Convert(val, cty.String)
		if err != nil {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid template interpolation value",
				Detail: fmt.Sprintf(
					"Cannot include one of the interpolation results into the string template: %s.",
					err.Error(),
				),
				Subject:     e.Range().Ptr(),
				Expression:  e,
				EvalContext: ctx,
			})
			continue
		}
		if !val.IsKnown() {
			return cty.UnknownVal(cty.String).WithMarks(marks), diags
		}

		strVal, strValMarks := strVal.Unmark()
		if len(strValMarks) > 0 {
			allMarks = append(allMarks, strValMarks)
		}
		buf.WriteString(strVal.AsString())
	}

	return cty.StringVal(buf.String()).WithMarks(allMarks...), diags
}

func (e *TemplateJoinExpr) Range() hcl.Range {
	return e.Tuple.Range()
}

func (e *TemplateJoinExpr) StartRange() hcl.Range {
	return e.Tuple.StartRange()
}

// TemplateWrapExpr is used instead of a TemplateExpr when a template
// consists _only_ of a single interpolation sequence. In that case, the
// template's result is the single interpolation's result, verbatim with
// no type conversions.
type TemplateWrapExpr struct {
	Wrapped Expression

	SrcRange hcl.Range
}

func (e *TemplateWrapExpr) walkChildNodes(w internalWalkFunc) {
	w(e.Wrapped)
}

func (e *TemplateWrapExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
	if e.Wrapped == nil {
		return cty.NilVal, nil
	}

	return e.Wrapped.Value(ctx)
}

func (e *TemplateWrapExpr) Range() hcl.Range {
	return e.SrcRange
}

func (e *TemplateWrapExpr) StartRange() hcl.Range {
	return e.SrcRange
}