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parse.go
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429 lines (371 loc) · 9.4 KB
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package spdxexp
import (
"errors"
"strings"
)
// The ABNF grammar in the spec is totally ambiguous.
//
// This parser follows the operator precedence defined in the
// `Order of Precedence and Parentheses` section.
type tokenStream struct {
tokens []token
index int
err error
}
func parse(source string) (*node, error) {
if len(source) == 0 {
return nil, errors.New("parse error - cannot parse empty string")
}
tokens, err := scan(source)
if err != nil {
return nil, err
}
tokns := &tokenStream{tokens: tokens, index: 0, err: nil}
return tokns.parseTokens(), tokns.err
}
func (t *tokenStream) parseTokens() *node {
if len(t.tokens) == 0 {
// malformed with no tokens
t.err = errors.New("no tokens to parse")
return nil
}
node := t.parseExpression()
if t.err != nil {
return nil
}
if node == nil {
// unable to parse expression for unknown reason
t.err = errors.New("syntax error")
return nil
} else if t.hasMore() {
// malformed with too many tokens - try to determine the cause
// check for close parenthesis without matching open parenthesis
closeParen := t.parseOperator(")")
if closeParen != nil {
t.err = errors.New("close parenthesis does not have a matching open parenthesis")
return nil
}
// check for licenses without operator
lic := t.parseLicense()
if lic != nil {
t.err = errors.New("licenses or expressions are not separated by an operator")
return nil
}
// cannot determine what syntax error occurred
t.err = errors.New("syntax error")
return nil
}
// all is well
return node
}
// Return true if there is another token to process; otherwise, return false.
func (t *tokenStream) hasMore() bool {
return t.index < len(t.tokens)
}
// Return the value of the next token without advancing the index.
func (t *tokenStream) peek() *token {
if t.hasMore() {
token := t.tokens[t.index]
return &token
}
return nil
}
// Advance the index to the next token.
func (t *tokenStream) next() {
if !t.hasMore() {
t.err = errors.New("read past end of tokens")
return
}
t.index++
}
func (t *tokenStream) parseParenthesizedExpression() *node {
openParen := t.parseOperator("(")
if openParen == nil {
// paren not found
return nil
}
expr := t.parseExpression()
if t.err != nil {
return nil
}
if !t.hasMore() {
// no more tokens, so missing closing paren
t.err = errors.New("open parenthesis does not have a matching close parenthesis")
return nil
}
closeParen := t.parseOperator(")")
if closeParen == nil {
t.err = errors.New("open parenthesis does not have a matching close parenthesis")
return nil
}
return expr
}
func (t *tokenStream) parseAtom() *node {
parenNode := t.parseParenthesizedExpression()
if t.err != nil {
return nil
}
if parenNode != nil {
return parenNode
}
refNode := t.parseLicenseRef()
if t.err != nil {
return nil
}
if refNode != nil {
return refNode
}
licenseNode := t.parseLicense()
if t.err != nil {
return nil
}
if licenseNode != nil {
return licenseNode
}
// no atom found - try to determine the cause
if t.hasMore() {
// check for operators
operator := t.parseOperator(")")
if operator != nil {
if t.index == 1 {
t.err = errors.New("expression starts with close parenthesis")
} else {
t.err = errors.New("expected license or expression, but found close parenthesis")
}
return nil
}
operator = t.parseOperator("OR")
if operator != nil {
if t.index == 1 {
t.err = errors.New("expression starts with OR")
} else {
t.err = errors.New("expected license or expression, but found OR")
}
return nil
}
operator = t.parseOperator("AND")
if operator != nil {
if t.index == 1 {
t.err = errors.New("expression starts with AND")
} else {
t.err = errors.New("expected license or expression, but found AND")
}
return nil
}
// cannot determine what syntax error occurred
t.err = errors.New("syntax error")
return nil
}
t.err = errors.New("expected node, but found none")
return nil
}
func (t *tokenStream) parseExpression() *node {
left := t.parseAnd()
if t.err != nil {
return nil
}
if left == nil {
return nil
}
if !t.hasMore() {
// expression found and no more tokens to process
return left
}
operator := t.parseOperator("OR")
if operator == nil {
return left
}
op := strings.ToLower(*operator)
if !t.hasMore() {
// expression found and no more tokens to process
t.err = errors.New("expected expression following OR, but found none")
return nil
}
right := t.parseExpression()
if t.err != nil {
return nil
}
if right == nil {
t.err = errors.New("expected expression following OR, but found none")
return nil
}
return &(node{
role: expressionNode,
exp: &(expressionNodePartial{
left: left,
conjunction: op,
right: right,
}),
})
}
// Return a node representation of an atomic value or an AND expression. If a malformed
// atomic value or expression is found, an error is returned. Advances the index if a
// valid atomic value or a valid expression is found.
func (t *tokenStream) parseAnd() *node {
left := t.parseAtom()
if t.err != nil {
return nil
}
if left == nil {
return nil
}
if !t.hasMore() {
// atomic token found and no more tokens to process
return left
}
operator := t.parseOperator("AND")
if operator == nil {
return left
}
if !t.hasMore() {
// expression found and no more tokens to process
t.err = errors.New("expected expression following AND, but found none")
return nil
}
right := t.parseAnd()
if t.err != nil {
return nil
}
if right == nil {
t.err = errors.New("expected expression following AND, but found none")
return nil
}
exp := expressionNodePartial{left: left, conjunction: "and", right: right}
return &(node{
role: expressionNode,
exp: &exp,
})
}
// Return a node representation of a License Reference. If a malformed license reference is
// found, an error is returned. Advances the index if a valid license reference is found.
func (t *tokenStream) parseLicenseRef() *node {
ref := referenceNodePartial{documentRef: "", hasDocumentRef: false, licenseRef: ""}
token := t.peek()
if token.role == documentRefToken {
ref.documentRef = token.value
ref.hasDocumentRef = true
t.next()
operator := t.parseOperator(":")
if operator == nil {
t.err = errors.New("expected ':' after 'DocumentRef-...'")
return nil
}
}
token = t.peek()
if token.role != licenseRefToken && ref.hasDocumentRef {
t.err = errors.New("expected 'LicenseRef-...' after 'DocumentRef-...'")
return nil
} else if token.role != licenseRefToken {
// not found is not an error as long as DocumentRef and : weren't the previous tokens
return nil
}
ref.licenseRef = token.value
t.next()
return &(node{
role: licenseRefNode,
ref: &ref,
})
}
// Return a node representation of a License. If a malformed license is found,
// an error is returned. Advances the index if a valid license is found.
func (t *tokenStream) parseLicense() *node {
token := t.peek()
if token.role != licenseToken {
return nil
}
t.next()
lic := licenseNodePartial{
license: token.value,
hasPlus: false,
hasException: false,
exception: ""}
// for licenses that specifically support -or-later, a `+` operator token isn't expected to be present
if strings.HasSuffix(token.value, "-or-later") {
lic.hasPlus = true
}
if t.hasMore() {
// use new var idx to avoid creating a new var index
operator := t.parseOperator("+")
if operator != nil {
lic.hasPlus = true
}
if t.hasMore() {
exception := t.parseWith()
if t.err != nil {
return nil
}
if exception != nil {
lic.hasException = true
lic.exception = *exception
t.next()
}
}
}
return &(node{
role: licenseNode,
lic: &lic,
})
}
// Return the operator's value (e.g. AND, OR, WITH) if the current token is an OPERATOR.
// Advances the index if the operator is found.
func (t *tokenStream) parseOperator(operator string) *string {
token := t.peek()
if token.role == operatorToken && token.value == operator {
t.next()
return &(token.value)
}
// requested operator not found
return nil
}
// Get the exception license when the WITH operator is found.
// Return without advancing the index if the current token is not the WITH operator.
// Raise an error if the WITH operator is not followed by and EXCEPTION license.
func (t *tokenStream) parseWith() *string {
operator := t.parseOperator("WITH")
if operator == nil {
// WITH not found is not an error
return nil
}
token := t.peek()
if token == nil || token.role != exceptionToken {
t.err = errors.New("expected exception after 'WITH'")
return nil
}
return &(token.value)
}
// Returns a human readable representation of the node tree.
func (n *node) string() string {
switch n.role {
case expressionNode:
return expressionString(*n.exp)
case licenseNode:
return licenseString(*n.lic)
case licenseRefNode:
return referenceString(*n.ref)
}
return ""
}
func expressionString(exp expressionNodePartial) string {
s := "{ LEFT: " + exp.left.string() + " "
s += exp.conjunction
s += " RIGHT: " + exp.right.string() + " }"
return s
}
func licenseString(lic licenseNodePartial) string {
s := lic.license
if lic.hasPlus {
s += "+"
}
if lic.hasException {
s += " with " + lic.exception
}
return s
}
func referenceString(ref referenceNodePartial) string {
s := ""
if ref.hasDocumentRef {
s = "DocumentRef-" + ref.documentRef + ":"
}
s += "LicenseRef-" + ref.licenseRef
return s
}