add initial stubs for model reconstruction trail

src/ast/simplifiers/model_reconstruction_trail.h

@@ -0,0 +1,80 @@
+/*++
+Copyright (c) 2022 Microsoft Corporation
+
+Module Name:
+
+    model_reconstruction_trail.h
+
+Abstract:
+
+   Model reconstruction trail
+   A model reconstruction trail comprises of a sequence of assignments 
+   together with assertions that were removed in favor of the assignments. 
+   The assignments satisfy the removed assertions but are not (necessarily) 
+   equivalent to the removed assertions. For the case where assignments 
+   are equivalent to removed assertions, we squash the removed assertions 
+   and don't track them.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2022-11-3.
+    
+--*/
+
+#pragma once
+
+#include "util/scoped_ptr_vector.h"
+#include "ast/rewriter/expr_replacer.h"
+#include "ast/simplifiers/dependent_expr.h"
+#include "ast/converters/model_converter.h"
+
+class model_reconstruction_trail {
+
+    ast_manager& m;
+
+    struct model_reconstruction_trail_entry {
+        scoped_ptr<expr_replacer> m_replace;
+        vector<dependent_expr>    m_removed;
+        model_reconstruction_trail_entry(expr_replacer* r, vector<dependent_expr> const& rem) :
+            m_replace(r), m_removed(rem) {}
+    };
+
+    scoped_ptr_vector<model_reconstruction_trail_entry> m_trail;
+    unsigned_vector m_limit;
+
+public:
+
+    model_reconstruction_trail(ast_manager& m) : m(m) {}
+
+    /**
+    * add a new substitution to the stack
+    */
+    void push(expr_replacer* r, vector<dependent_expr> const& removed) {
+        m_trail.push_back(alloc(model_reconstruction_trail_entry, r, removed));
+    }
+
+    /**
+    * register a new depedent expression, update the trail 
+    * by removing substitutions that are not equivalence preserving.
+    */
+    void replay(dependent_expr const& d, vector<dependent_expr>& added);
+
+    /**
+    * retrieve the current model converter corresponding to chaining substitutions from the trail.
+    */
+    model_converter_ref get_model_converter();
+
+    /**
+    * push a context. Portions of the trail added within a context are removed after a context pop.
+    */
+    void push() {
+        m_limit.push_back(m_trail.size());
+    }
+
+    void pop(unsigned n) {
+        unsigned old_sz = m_limit[m_limit.size() - n];
+        m_trail.resize(old_sz);
+        m_limit.shrink(m_limit.size() - n);
+    }
+};
+