317 lines
18 KiB
Swift
317 lines
18 KiB
Swift
extension PureXML.Schema {
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/// XSD 1.0 "Particle Valid (Restriction)" for the common cases: a complex
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/// type derived by restriction must have a content model that accepts a
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/// subset of its base's. Covers element-vs-element name matching,
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/// element-vs-wildcard admission, wildcard narrowing, occurrence-range
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/// subsumption, and the group recursions (sequence/all order-preserving with
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/// emptiable skips, choice mapping, sequence-into-choice, sequence-into-all).
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/// The spec's effective-total-range arithmetic for MapAndSum is approximated
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/// by per-particle checks, a documented simplification.
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enum ParticleRestriction {
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/// The reason a restriction's content is not a valid subset of its
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/// base's, or nil when it is. `types` resolves an element's
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/// ``ElementType/typeReference`` so element-vs-element pairs can check that
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/// the restricting type derives from the base's (NameAndTypeOK).
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static func violation(restricted: ContentType, base: ContentType, types: [String: ElementType], derivation: [String: TypeDerivation]) -> String? {
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switch (restricted, base) {
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case (.empty, .empty), (.simpleContent, _), (_, .simpleContent):
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nil
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case let (.empty, .elementOnly(baseParticle)), let (.empty, .mixed(baseParticle)):
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emptiable(baseParticle) ? nil : "the base content is required, so the restriction cannot be EMPTY"
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case (.mixed, .elementOnly):
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"a restriction cannot add mixed content to an element-only base"
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case let (.elementOnly(restrictedParticle), .empty):
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// A content-free particle (an empty group, or one whose members all
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// have maxOccurs=0) accepts only the empty sequence, so it is a valid
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// restriction of EMPTY; only a particle that can contribute a child is
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// adding content.
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contentFree(restrictedParticle) ? nil : "the base content is EMPTY, so the restriction cannot add content"
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case (.mixed, .empty):
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"the base content is EMPTY, so the restriction cannot add content"
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case let (.elementOnly(restrictedParticle), .elementOnly(baseParticle)),
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let (.elementOnly(restrictedParticle), .mixed(baseParticle)),
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let (.mixed(restrictedParticle), .mixed(baseParticle)):
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// The W3C restriction algorithm is defined over the normalized content
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// model (pointless particles eliminated): a `maxOccurs=0` member
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// removed, a `{1,1}` single-member group unwrapped, a nested
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// same-compositor `{1,1}` group spliced. Without this, e.g. a base
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// `sequence(any{2,3})` is not seen as the wildcard it equals.
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valid(restrictedParticle.normalized(), baseParticle.normalized(), types, derivation)
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? nil
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: "the restricted content model is not a subset of the base's"
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}
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}
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/// Whether `restricted` accepts a subset of `base` (the pairwise check).
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///
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/// Occurrence subsumption (`rangeSubsumed`) is applied only to the
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/// same-kind pairings (element/element, wildcard/wildcard, group/group) and
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/// element/wildcard, where the two particles' own occurrence ranges are
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/// directly comparable. For the cross-kind pairings (element/group and
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/// group/element via RecurseAsIfGroup; group/wildcard via
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/// NSRecurseCheckCardinality) the occurrence is matched *inside* the case,
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/// against a member or as an effective total range, never the derived
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/// particle's own occurrence against the base group/wildcard's. Applying the
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/// outer check there over-rejects: e.g. `sequence(e1{2,3})` restricting
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/// `sequence(e1{1,3},...)` once the pointless single-member group is
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/// normalized to the bare `e1{2,3}` (`3 > 1` against the base sequence).
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static func valid(_ restricted: Particle, _ base: Particle, _ types: [String: ElementType], _ derivation: [String: TypeDerivation]) -> Bool {
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// A restriction that can never contribute a child (its own `maxOccurs=0`,
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// or a group whose every member is content-free) accepts only the empty
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// sequence, so it is a valid restriction of any emptiable base. Checked
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// before the structural cases, which would otherwise recurse into members
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// that never occur and wrongly reject (e.g. a `maxOccurs="0"` sequence
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// whose members have their own non-trivial occurrences).
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if contentFree(restricted) {
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return emptiable(base)
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}
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switch (restricted.term, base.term) {
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case let (.element(restrictedName, _, restrictedTypeName), .element(baseName, _, baseTypeName)):
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return rangeSubsumed(restricted, base)
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&& sameName(restrictedName, baseName)
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&& elementTypeRestrictionOK(restrictedTypeName, baseTypeName, types, derivation)
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case let (.element(name, _, _), .wildcard(wildcard)):
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return rangeSubsumed(restricted, base) && wildcard.admits(name)
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case let (.wildcard(restrictedWildcard), .wildcard(baseWildcard)):
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return rangeSubsumed(restricted, base) && narrows(restrictedWildcard, baseWildcard)
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case let (.element, .group(baseGroup)):
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// RecurseAsIfGroup: the lone element, as a one-particle sequence,
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// against the base group. The element's occurrence is matched against
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// a base member inside `groupValid`, not against the base group's own
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// occurrence, so no outer `rangeSubsumed` here.
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return groupValid(Group(compositor: .sequence, particles: [restricted]), baseGroup, types, derivation)
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case let (.group, .element(baseName, _, baseTypeName)):
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// The mirror of RecurseAsIfGroup, by the same cardinality argument as
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// group/wildcard: a base element accepts only its own name, its own
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// occurrence count of times. The derived group is a valid restriction
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// iff every leaf it can contain is that element (same name, and a type
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// that derives from the base's) AND the group's effective total
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// occurrence range is within the base element's. Comparing the derived
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// group's *own* occurrence to the element's would be wrong (a derived
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// `sequence(a,a)` emits two a's at occurrence {1,1}); the effective
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// range is the count that must be bounded.
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return leavesRestrict(restricted, toElement: baseName, baseTypeName, types, derivation)
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&& rangeWithinWildcard(
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derivedMin: restricted.effectiveOccurrenceMin(),
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derivedMax: restricted.effectiveOccurrenceMax(),
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wildcardMin: base.minOccurs,
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wildcardMax: base.maxOccurs,
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)
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case let (.group(restrictedGroup), .group(baseGroup)) where restrictedGroup.compositor == .sequence && baseGroup.compositor == .choice:
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// MapAndSum (Sequence:Choice, XSD 1.0 §3.9.6): each derived particle is
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// a valid restriction of some base branch, AND the derived sequence's
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// occurrence count times its number of particles is within the base
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// choice's occurrence range. The outer occurrence subsumption used by
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// the same-compositor cases is wrong here (it would compare a derived
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// `sequence{2,4}` directly to a base `choice{3,9}`); the count-product
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// is the spec's measure, deliberately stricter than a pure subset.
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let members = restrictedGroup.particles.filter { $0.maxOccurs != 0 }
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let branches = baseGroup.particles.filter { $0.maxOccurs != 0 }
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return rangeWithinWildcard(
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derivedMin: restricted.minOccurs * members.count,
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derivedMax: restricted.maxOccurs.map { $0 * members.count },
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wildcardMin: base.minOccurs,
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wildcardMax: base.maxOccurs,
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)
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&& members.allSatisfy { member in branches.contains { valid(member, $0, types, derivation) } }
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case let (.group(restrictedGroup), .group(baseGroup)):
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// A content-free derived group was already handled above; here the
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// derived group can contribute content, so its outer occurrence must be
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// subsumed and its members must map onto the base's.
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return rangeSubsumed(restricted, base) && groupValid(restrictedGroup, baseGroup, types, derivation)
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case let (.group, .wildcard(wildcard)):
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// NSRecurseCheckCardinality: every leaf the group can contain is
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// admitted by the wildcard (an element by name, a nested wildcard by
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// narrowing), AND the group's effective total occurrence range is
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// within the wildcard's occurrence range.
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return leavesAdmitted(restricted, by: wildcard)
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&& rangeWithinWildcard(
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derivedMin: restricted.effectiveOccurrenceMin(),
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derivedMax: restricted.effectiveOccurrenceMax(),
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wildcardMin: base.minOccurs,
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wildcardMax: base.maxOccurs,
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)
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default:
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return false
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}
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}
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private static func groupValid(_ restricted: Group, _ base: Group, _ types: [String: ElementType], _ derivation: [String: TypeDerivation]) -> Bool {
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// A particle that can never occur (maxOccurs=0) contributes nothing to the
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// language, so it is removed before mapping (a "pointless particle"). Left
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// in, it would wrongly consume a base particle and starve the particles
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// after it (e.g. `(e1 maxOccurs=0, e2)` restricting `(any)`).
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let restrictedParticles = restricted.particles.filter { $0.maxOccurs != 0 }
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let baseParticles = base.particles.filter { $0.maxOccurs != 0 }
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switch (restricted.compositor, base.compositor) {
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case (.sequence, .sequence), (.all, .all):
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return recurse(restrictedParticles, baseParticles, skippedMustBeEmptiable: true, types, derivation)
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case (.choice, .choice):
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// RecurseLax: an order-preserving mapping (W3C requires it; a choice
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// `(b|a)` is NOT a valid restriction of `(a|b)`), but skipped base
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// branches need not be emptiable. The base's substitution-group
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// expansion must therefore be in document order for this to be right.
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return recurse(restrictedParticles, baseParticles, skippedMustBeEmptiable: false, types, derivation)
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case (.sequence, .choice):
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// RecurseAsIfGroup for an element against a base choice arrives here as a
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// one-particle synthetic sequence: each derived particle fits some base
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// branch. (A genuine multi-particle sequence restricting a choice is
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// handled by MapAndSum at the particle level, where the occurrence
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// count-product is available.)
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return restrictedParticles.allSatisfy { particle in
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baseParticles.contains { valid(particle, $0, types, derivation) }
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}
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case (.sequence, .all):
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// RecurseUnordered: map onto distinct base particles in any order.
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return recurseUnordered(restrictedParticles, baseParticles, types, derivation)
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default:
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return false
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}
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}
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/// Whether a particle can never contribute a child element or wildcard: it
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/// has `maxOccurs=0`, or is a group all of whose members are content-free
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/// (an empty group included). Its only legal content is the empty sequence.
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static func contentFree(_ particle: Particle) -> Bool {
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if particle.maxOccurs == 0 { return true }
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switch particle.term {
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case .element, .wildcard:
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return false
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case let .group(group):
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return group.particles.allSatisfy(contentFree)
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}
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}
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/// Order-preserving mapping of the restricted particles onto the base's.
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/// A skipped base particle must be emptiable for sequence/all (Recurse);
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/// for choice (RecurseLax) skipping is free.
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private static func recurse(
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_ restricted: [Particle],
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_ base: [Particle],
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skippedMustBeEmptiable: Bool,
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_ types: [String: ElementType],
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_ derivation: [String: TypeDerivation],
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) -> Bool {
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var baseIndex = 0
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for particle in restricted {
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var matched = false
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while baseIndex < base.count {
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let candidate = base[baseIndex]
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baseIndex += 1
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if valid(particle, candidate, types, derivation) {
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matched = true
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break
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}
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if skippedMustBeEmptiable, !emptiable(candidate) { return false }
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}
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if !matched { return false }
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}
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if skippedMustBeEmptiable {
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while baseIndex < base.count {
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if !emptiable(base[baseIndex]) { return false }
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baseIndex += 1
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}
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}
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return true
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}
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/// Any-order mapping onto distinct base particles; unmapped base
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/// particles must be emptiable.
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private static func recurseUnordered(_ restricted: [Particle], _ base: [Particle], _ types: [String: ElementType], _ derivation: [String: TypeDerivation]) -> Bool {
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var used = [Bool](repeating: false, count: base.count)
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for particle in restricted {
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guard let index = base.indices.first(where: { !used[$0] && valid(particle, base[$0], types, derivation) }) else {
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return false
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}
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used[index] = true
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}
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return base.indices.allSatisfy { used[$0] || emptiable(base[$0]) }
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}
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/// Occurrence-range subsumption: the restriction may not occur less often
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/// than the base requires, nor more often than the base allows.
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private static func rangeSubsumed(_ restricted: Particle, _ base: Particle) -> Bool {
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guard restricted.minOccurs >= base.minOccurs else { return false }
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guard let baseMax = base.maxOccurs else { return true }
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guard let restrictedMax = restricted.maxOccurs else { return false }
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return restrictedMax <= baseMax
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}
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/// Whether a particle can match no children at all.
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static func emptiable(_ particle: Particle) -> Bool {
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if particle.minOccurs == 0 { return true }
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switch particle.term {
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case .element, .wildcard:
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return false
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case let .group(group):
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switch group.compositor {
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case .sequence, .all:
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return group.particles.allSatisfy(emptiable)
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case .choice:
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return group.particles.contains(where: emptiable)
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}
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}
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}
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/// Whether the restricted wildcard admits no namespace the base refuses.
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private static func narrows(_ restricted: Wildcard, _ base: Wildcard) -> Bool {
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switch (restricted.namespace, base.namespace) {
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case (_, .any):
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true
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case (.other, .other):
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restricted.targetNamespace == base.targetNamespace
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case let (.enumerated(narrow), .enumerated(wide)):
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narrow.isSubset(of: wide)
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case let (.enumerated(narrow), .other):
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!narrow.contains("") && !narrow.contains(base.targetNamespace ?? "")
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default:
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false
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}
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}
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private static func sameName(_ lhs: PureXML.Model.QualifiedName, _ rhs: PureXML.Model.QualifiedName) -> Bool {
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lhs.localName == rhs.localName && (lhs.namespaceURI ?? "") == (rhs.namespaceURI ?? "")
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}
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/// Whether every leaf a particle can contain is admitted by `wildcard`: an
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/// element by name, a nested wildcard by narrowing.
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private static func leavesAdmitted(_ particle: Particle, by wildcard: Wildcard) -> Bool {
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switch particle.term {
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case let .element(name, _, _): wildcard.admits(name)
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case let .wildcard(inner): narrows(inner, wildcard)
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case let .group(group): group.particles.allSatisfy { leavesAdmitted($0, by: wildcard) }
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}
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}
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/// Whether every leaf a particle can contain is the named base element (same
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/// name, and a type that derives from the base element's). A wildcard leaf is
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/// rejected: it can match names other than the base element's, so it is not a
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/// subset. Used when the base content model is a single element.
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private static func leavesRestrict(
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_ particle: Particle,
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toElement baseName: PureXML.Model.QualifiedName,
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_ baseTypeName: String?,
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_ types: [String: ElementType],
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_ derivation: [String: TypeDerivation],
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) -> Bool {
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switch particle.term {
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case let .element(name, _, typeName):
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sameName(name, baseName) && elementTypeRestrictionOK(typeName, baseTypeName, types, derivation)
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case .wildcard:
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false
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case let .group(group):
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group.particles.allSatisfy { leavesRestrict($0, toElement: baseName, baseTypeName, types, derivation) }
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}
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}
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/// Whether a derived effective total range fits within a base wildcard's
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/// occurrence range: at least the wildcard's minimum, at most its maximum.
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private static func rangeWithinWildcard(derivedMin: Int, derivedMax: Int?, wildcardMin: Int, wildcardMax: Int?) -> Bool {
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guard derivedMin >= wildcardMin else { return false }
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guard let wildcardMax else { return true }
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guard let derivedMax else { return false }
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return derivedMax <= wildcardMax
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}
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}
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}
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