(proof-new) Add trust node utility (#4588)

This is a core data structure for associating a formula with a proof generator.

3 files changed, 257 insertions, 0 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 44b5dfeaf..1820fbb5d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -746,6 +746,8 @@ libcvc4_add_sources(
   theory/theory_model_builder.h
   theory/theory_registrar.h
   theory/theory_test_utils.h
+  theory/trust_node.cpp
+  theory/trust_node.h
   theory/type_enumerator.h
   theory/type_set.cpp
   theory/type_set.h
diff --git a/src/theory/trust_node.cpp b/src/theory/trust_node.cpp
new file mode 100644
index 000000000..ff3e89154
--- /dev/null
+++ b/src/theory/trust_node.cpp
@@ -0,0 +1,102 @@
+/*********************                                                        */
+/*! \file trust_node.cpp
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds
+ ** This file is part of the CVC4 project.
+ ** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
+ ** in the top-level source directory) and their institutional affiliations.
+ ** All rights reserved.  See the file COPYING in the top-level source
+ ** directory for licensing information.\endverbatim
+ **
+ ** \brief Implementation of the trust node utility
+ **/
+
+#include "theory/trust_node.h"
+
+#include "expr/proof_generator.h"
+
+namespace CVC4 {
+namespace theory {
+
+const char* toString(TrustNodeKind tnk)
+{
+  switch (tnk)
+  {
+    case TrustNodeKind::CONFLICT: return "CONFLICT";
+    case TrustNodeKind::LEMMA: return "LEMMA";
+    case TrustNodeKind::PROP_EXP: return "PROP_EXP";
+    default: return "?";
+  }
+}
+
+std::ostream& operator<<(std::ostream& out, TrustNodeKind tnk)
+{
+  out << toString(tnk);
+  return out;
+}
+
+TrustNode TrustNode::mkTrustConflict(Node conf, ProofGenerator* g)
+{
+  Node ckey = getConflictProven(conf);
+  // if a generator is provided, should confirm that it can prove it
+  Assert(g == nullptr || g->hasProofFor(ckey));
+  return TrustNode(TrustNodeKind::CONFLICT, ckey, g);
+}
+
+TrustNode TrustNode::mkTrustLemma(Node lem, ProofGenerator* g)
+{
+  Node lkey = getLemmaProven(lem);
+  // if a generator is provided, should confirm that it can prove it
+  Assert(g == nullptr || g->hasProofFor(lkey));
+  return TrustNode(TrustNodeKind::LEMMA, lkey, g);
+}
+
+TrustNode TrustNode::mkTrustPropExp(TNode lit, Node exp, ProofGenerator* g)
+{
+  Node pekey = getPropExpProven(lit, exp);
+  Assert(g == nullptr || g->hasProofFor(pekey));
+  return TrustNode(TrustNodeKind::PROP_EXP, pekey, g);
+}
+
+TrustNode TrustNode::null()
+{
+  return TrustNode(TrustNodeKind::INVALID, Node::null());
+}
+
+TrustNode::TrustNode(TrustNodeKind tnk, Node p, ProofGenerator* g)
+    : d_tnk(tnk), d_proven(p), d_gen(g)
+{
+  // does not make sense to provide null node with generator
+  Assert(!d_proven.isNull() || d_gen == nullptr);
+}
+
+TrustNodeKind TrustNode::getKind() const { return d_tnk; }
+
+Node TrustNode::getNode() const
+{
+  return d_tnk == TrustNodeKind::LEMMA ? d_proven : d_proven[0];
+}
+
+Node TrustNode::getProven() const { return d_proven; }
+ProofGenerator* TrustNode::getGenerator() const { return d_gen; }
+
+bool TrustNode::isNull() const { return d_proven.isNull(); }
+
+Node TrustNode::getConflictProven(Node conf) { return conf.notNode(); }
+
+Node TrustNode::getLemmaProven(Node lem) { return lem; }
+
+Node TrustNode::getPropExpProven(TNode lit, Node exp)
+{
+  return NodeManager::currentNM()->mkNode(kind::IMPLIES, exp, lit);
+}
+
+std::ostream& operator<<(std::ostream& out, TrustNode n)
+{
+  out << "(trust " << n.getNode() << ")";
+  return out;
+}
+
+}  // namespace theory
+}  // namespace CVC4
diff --git a/src/theory/trust_node.h b/src/theory/trust_node.h
new file mode 100644
index 000000000..f5d6382d2
--- /dev/null
+++ b/src/theory/trust_node.h
@@ -0,0 +1,153 @@
+/*********************                                                        */
+/*! \file trust_node.h
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Andrew Reynolds
+ ** This file is part of the CVC4 project.
+ ** Copyright (c) 2009-2019 by the authors listed in the file AUTHORS
+ ** in the top-level source directory) and their institutional affiliations.
+ ** All rights reserved.  See the file COPYING in the top-level source
+ ** directory for licensing information.\endverbatim
+ **
+ ** \brief The trust node utility
+ **/
+
+#include "cvc4_private.h"
+
+#ifndef CVC4__THEORY__TRUST_NODE_H
+#define CVC4__THEORY__TRUST_NODE_H
+
+#include "expr/node.h"
+
+namespace CVC4 {
+
+class ProofGenerator;
+
+namespace theory {
+
+/** A kind for trust nodes */
+enum class TrustNodeKind : uint32_t
+{
+  CONFLICT,
+  LEMMA,
+  PROP_EXP,
+  INVALID
+};
+/**
+ * Converts a proof rule to a string. Note: This function is also used in
+ * `safe_print()`. Changing this function name or signature will result in
+ * `safe_print()` printing "<unsupported>" instead of the proper strings for
+ * the enum values.
+ *
+ * Returns a string with static lifetime: it should not be freed.
+ *
+ * @param tnk The trust node kind
+ * @return The name of the trust node kind
+ */
+const char* toString(TrustNodeKind tnk);
+
+/**
+ * Writes a trust node kind name to a stream.
+ *
+ * @param out The stream to write to
+ * @param tnk The trust node kind to write to the stream
+ * @return The stream
+ */
+std::ostream& operator<<(std::ostream& out, TrustNodeKind tnk);
+
+/**
+ * A trust node is a pair (F, G) where F is a formula and G is a proof
+ * generator that can construct a proof for F if asked.
+ *
+ * More generally, a trust node is any node that can be used for a specific
+ * purpose that requires justification, such as being passed to
+ * OutputChannel::lemma. That justification is intended to be given by the
+ * generator that is required to construct this object.
+ *
+ * They are intended to be constructed by ProofGenerator objects themselves (a
+ * proof generator wraps itself in TrustNode it returns) and passed
+ * to ProofOutputChannel by theory solvers.
+ *
+ * The static functions for constructing them check that the generator, if
+ * provided, is capable of proving the given conflict or lemma, or an assertion
+ * failure occurs. Otherwise an assertion error is given.
+ *
+ * While this is not enforced, a `TrustNode` generally encapsulates a **closed** proof
+ * of the formula: one without free assumptions.
+ */
+class TrustNode
+{
+ public:
+  TrustNode() : d_tnk(TrustNodeKind::INVALID), d_gen(nullptr) {}
+  /** Make a proven node for conflict */
+  static TrustNode mkTrustConflict(Node conf, ProofGenerator* g = nullptr);
+  /** Make a proven node for lemma */
+  static TrustNode mkTrustLemma(Node lem, ProofGenerator* g = nullptr);
+  /** Make a proven node for explanation of propagated literal */
+  static TrustNode mkTrustPropExp(TNode lit,
+                                  Node exp,
+                                  ProofGenerator* g = nullptr);
+  /** The null proven node */
+  static TrustNode null();
+  ~TrustNode() {}
+  /** get kind */
+  TrustNodeKind getKind() const;
+  /** get node
+   *
+   * This is the node that is used in a common interface, either:
+   * (1) A T-unsat conjunction conf to pass to OutputChannel::conflict,
+   * (2) A valid T-formula lem to pass to OutputChannel::lemma, or
+   * (3) A conjunction of literals exp to return in Theory::explain(lit).
+   *
+   * Notice that this node does not necessarily correspond to a valid formula.
+   * The call getProven() below retrieves a valid formula corresponding to
+   * the above calls.
+   */
+  Node getNode() const;
+  /** get proven
+   *
+   * This is the corresponding formula that is proven by the proof generator
+   * for the above cases:
+   * (1) (not conf), for conflicts,
+   * (2) lem, for lemmas,
+   * (3) (=> exp lit), for propagations from explanations.
+   *
+   * When constructing this trust node, the proof generator should be able to
+   * provide a proof for this fact.
+   */
+  Node getProven() const;
+  /** get generator */
+  ProofGenerator* getGenerator() const;
+  /** is null? */
+  bool isNull() const;
+
+  /** Get the proven formula corresponding to a conflict call */
+  static Node getConflictProven(Node conf);
+  /** Get the proven formula corresponding to a lemma call */
+  static Node getLemmaProven(Node lem);
+  /** Get the proven formula corresponding to explanations for propagation*/
+  static Node getPropExpProven(TNode lit, Node exp);
+
+ private:
+  TrustNode(TrustNodeKind tnk, Node p, ProofGenerator* g = nullptr);
+  /** The kind */
+  TrustNodeKind d_tnk;
+  /** The proven node */
+  Node d_proven;
+  /** The generator */
+  ProofGenerator* d_gen;
+};
+
+/**
+ * Writes a trust node to a stream.
+ *
+ * @param out The stream to write to
+ * @param n The trust node to write to the stream
+ * @return The stream
+ */
+std::ostream& operator<<(std::ostream& out, TrustNode n);
+
+}  // namespace theory
+}  // namespace CVC4
+
+#endif /* CVC4__THEORY__TRUST_NODE_H */