Derive with ranges (#9965)

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Margus Veanes <margus@microsoft.com>
Co-authored-by: Margus Veanes <veanes@users.noreply.github.com>

src/ast/rewriter/seq_range_collapse.h

@@ -0,0 +1,71 @@
+/*++
+Copyright (c) 2026 Microsoft Corporation
+
+Module Name:
+
+    seq_range_collapse.h
+
+Abstract:
+
+    Recognize regexes that are boolean combinations of character-class
+    primitives (re.empty, re.full_char, re.range with concrete chars,
+    and re.union/inter/comp/diff over translatable arguments), and
+    materialize a seq::range_predicate back into a canonical regex AST.
+
+    Together with seq_rewriter integration, this lets any boolean
+    combination of character-class regexes collapse to a canonical
+    multi-range form, so that equivalent character classes share AST
+    identity, and downstream consumers (derivative, OneStep, caching)
+    can short-circuit them as pure range predicates.
+
+Authors:
+
+    Margus Veanes (veanes) 2026
+
+--*/
+#pragma once
+
+#include "ast/rewriter/seq_range_predicate.h"
+#include "ast/seq_decl_plugin.h"
+
+namespace seq {
+
+    /**
+     * If r is a boolean combination of character-class regex primitives
+     * over the unsigned character domain [0, max_char], compute the
+     * equivalent range_predicate and return true. Otherwise return false
+     * with out untouched.
+     *
+     * Recognized fragment (all character-class-preserving operations):
+     *   re.empty                              -> empty
+     *   re.full_char_set                      -> top
+     *   re.range "c_lo" "c_hi"  (concrete)    -> [c_lo, c_hi]
+     *   re.union r1 r2                        -> p1 | p2
+     *   re.intersection r1 r2                 -> p1 & p2
+     *   re.diff r1 r2                         -> p1 - p2
+     *
+     * Notably re.complement is NOT recognized: it is a SEQUENCE-level
+     * complement (over all of Σ*), not a character-class complement, so
+     * collapsing it would change semantics whenever the result is used
+     * in any non-character-class context.  Sequence-level rewrites for
+     * re.complement (double-comp, deMorgan, etc.) are handled directly
+     * in seq_rewriter::mk_re_complement.
+     */
+    bool regex_to_range_predicate(seq_util& u, expr* r, range_predicate& out);
+
+    /**
+     * Canonical materialization of p as a regex AST over the given
+     * sequence sort. Two range_predicates with equal canonical
+     * representations produce structurally identical regex ASTs:
+     *
+     *   empty                  -> re.empty
+     *   top                    -> re.full_char_set
+     *   single range [lo, hi]  -> re.range "lo" "hi"
+     *   multiple ranges        -> right-associated re.union of single
+     *                              ranges, in increasing order of lo
+     *                              (matching the canonical range order
+     *                              held by range_predicate).
+     */
+    expr_ref range_predicate_to_regex(seq_util& u, range_predicate const& p, sort* seq_sort);
+
+}