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UnboundList.qll
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195 lines (163 loc) · 6.12 KB
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/**
* Provides logic for representing unbound lists.
*
* The lists are represented internally as strings, and generally it should
* be preferred to instead use a `newtype` representation, but in certain
* cases where this is not feasible (typically because of performance) unbound
* lists can be used.
*/
overlay[local?]
module;
private import Location
/** Provides the input to `Make`. */
signature module InputSig<LocationSig Location> {
/** An element. */
class Element {
/** Gets a textual representation of this element. */
string toString();
/** Gets the location of this element. */
Location getLocation();
}
/** Gets a unique ID used to identify element `e` amongst all elements. */
int getId(Element e);
/**
* Gets a textual representation for element `e`, which will be used in the
* `toString` representation for unbound lists.
*/
default string getElementString(Element e) { result = e.toString() }
/** Gets an optional length limit for unbound lists. */
default int getLengthLimit() { none() }
}
final private class String = string;
/** Provides the `UnboundList` implementation. */
module Make<LocationSig Location, InputSig<Location> Input> {
private import Input
private import codeql.util.DenseRank
// Use dense ranking to assign compact IDs to elements
private module DenseRankInput implements DenseRankInputSig {
class Ranked = Element;
predicate getRank = getId/1;
}
/** Gets the rank of element `e`, which is used internally in the string encoding. */
int getRank(Element e) { e = DenseRank<DenseRankInput>::denseRank(result) }
private string encode(Element e) { result = getRank(e).toString() }
bindingset[s]
private Element decode(string s) { encode(result) = s }
/**
* An unbound list encoded as a string.
*/
class UnboundList extends String {
bindingset[this]
UnboundList() { exists(this) }
/** Gets the `i`th element in this list. */
bindingset[this]
Element getElement(int i) { result = decode(this.splitAt(".", i)) }
/** Gets a textual representation of this list. */
bindingset[this]
string toString() {
result =
concat(int i, Element e | e = this.getElement(i) | getElementString(e), "." order by i)
}
/** Holds if this list is empty. */
predicate isEmpty() { this = "" }
bindingset[this]
private int stringLength() { result = super.length() }
/** Gets the length of this list. */
bindingset[this]
pragma[inline_late]
int length() {
// Same as
// `result = count(this.indexOf("."))`
// but performs better because it doesn't use an aggregate
result = this.regexpReplaceAll("[0-9]+", "").length()
}
/** Gets the list obtained by appending `suffix` onto this list. */
bindingset[this, suffix]
UnboundList append(UnboundList suffix) {
result = this + suffix and
(
not exists(getLengthLimit())
or
result.length() <= getLengthLimit()
)
}
/**
* Gets the list obtained by appending `suffix` onto this list.
*
* Unlike `append`, this predicate has `result` in the binding set,
* so there is no need to check the length of `result`.
*/
bindingset[this, result]
UnboundList appendInverse(UnboundList suffix) { suffix = result.stripPrefix(this) }
/** Gets the list obtained by removing `prefix` from this list. */
bindingset[this, prefix]
UnboundList stripPrefix(UnboundList prefix) { this = prefix + result }
/** Holds if this list starts with `e`, followed by `suffix`. */
bindingset[this]
predicate isCons(Element e, UnboundList suffix) {
exists(string elem |
// it is more efficient to not create a capture group for the suffix, since
// `regexpCapture` will then always join in both groups, only to afterwards filter
// based on the requested group (the group number is not part of the binding set
// of `regexpCapture`)
elem = this.regexpCapture("^([0-9]+)\\..*$", 1) and
e = decode(elem) and
suffix = this.suffix(elem.length() + 1)
)
}
/** Holds if this list starts with `prefix`, followed by `e`. */
bindingset[this]
predicate isSnoc(UnboundList prefix, Element e) {
// same remark as above about not using multiple capture groups
prefix = this.regexpCapture("^(|.+\\.)[0-9]+\\.$", 1) and
e = decode(this.substring(prefix.stringLength(), this.stringLength() - 1))
}
/** Gets the head of this list, if any. */
bindingset[this]
Element getHead() { result = this.getElement(0) }
/**
* Gets the `i`th prefix of this list, if any.
*
* Only holds when this list is non-empty, and only returns proper prefixes.
*/
bindingset[this]
UnboundList getProperPrefix(int i) {
exists(string regexp, int occurrenceOffset | regexp = "[0-9]+\\." |
exists(this.regexpFind(regexp, i, occurrenceOffset)) and
result = this.prefix(occurrenceOffset)
)
}
/**
* Gets a prefix of this list, if any.
*
* Only holds when this list is non-empty, and only returns proper prefixes.
*/
bindingset[this]
UnboundList getAProperPrefix() { result = this.getProperPrefix(_) }
/**
* Gets a prefix of this list, including the list itself.
*/
bindingset[this]
UnboundList getAPrefix() { result = [this, this.getAProperPrefix()] }
/**
* Holds if this list is a prefix of `other`.
*
* This is equivalent to `this = other.getAPrefix()`, but more performant.
*/
bindingset[this, other]
predicate isPrefixOf(UnboundList other) { this = other.prefix(this.stringLength()) }
}
/** Provides predicates for constructing `UnboundList`s. */
module UnboundList {
/** Gets the empty list. */
UnboundList nil() { result.isEmpty() }
/** Gets the singleton list `e`. */
UnboundList singleton(Element e) { result = encode(e) + "." }
/**
* Gets the list obtained by appending the singleton list `e`
* onto `suffix`.
*/
bindingset[suffix]
UnboundList cons(Element e, UnboundList suffix) { result = singleton(e).append(suffix) }
}
}