From 86af31327dbff6f206a15e3172a8bedb18157c66 Mon Sep 17 00:00:00 2001
From: natsuoto <279971144+natsuoto@users.noreply.github.com>
Date: Wed, 15 Jul 2026 14:37:38 +0530
Subject: feat(builder): RegexBuilder.from_regex reverse parser for the common
 construct set

---
 tests/builder/reverse.test.py | 113 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 tests/builder/reverse.test.py

(limited to 'tests/builder/reverse.test.py')

diff --git a/tests/builder/reverse.test.py b/tests/builder/reverse.test.py
new file mode 100644
index 0000000..1ed00ec
--- /dev/null
+++ b/tests/builder/reverse.test.py
@@ -0,0 +1,113 @@
+"""Tests for :meth:`RegexBuilder.from_regex` — the reverse parser."""
+
+import re
+
+import pytest
+
+from edify import RegexBuilder
+from edify.builder.reverse import UnsupportedReverseParseError
+
+
+@pytest.mark.parametrize(
+    ("source", "expected"),
+    [
+        ("hello", "hello"),
+        ("a", "a"),
+        (r"\d+", r"\d+"),
+        (r"\d*", r"\d*"),
+        (r"\d?", r"\d?"),
+        (r"\d{3}", r"\d{3}"),
+        (r"\d{2,5}", r"\d{2,5}"),
+        (r"\d{2,}", r"\d{2,}"),
+        (r"\w", r"\w"),
+        (r"\W", r"\W"),
+        (r"\s", r"\s"),
+        (r"\S", r"\S"),
+        (r"\D", r"\D"),
+        ("[a-z]", "[a-z]"),
+        ("[abc]", "[abc]"),
+        ("^", "^"),
+        ("$", "$"),
+        (r"\b", r"\b"),
+        (r"\B", r"\B"),
+        (".", "."),
+        ("(?:foo)", "foo"),
+        ("(abc)", "(abc)"),
+        ("(?P<name>abc)", "(?P<name>abc)"),
+        ("foo|bar", "(?:foo|bar)"),
+        ("(?=x)y", "(?=x)y"),
+        ("(?!x)y", "(?!x)y"),
+        ("(?<=x)y", "(?<=x)y"),
+        ("(?<!x)y", "(?<!x)y"),
+    ],
+)
+def test_from_regex_translates_common_constructs_faithfully(source, expected):
+    builder = RegexBuilder.from_regex(source)
+    assert builder.to_regex_string() == expected
+
+
+@pytest.mark.parametrize(
+    "source",
+    [
+        "hello",
+        r"\d+",
+        "^abc$",
+        r"[a-z]+",
+        "(?P<x>abc)",
+        "foo|bar",
+        r"(?=x)\w+",
+    ],
+)
+def test_round_trip_compiled_regex_matches_the_same_inputs(source):
+    original = re.compile(source)
+    reversed_builder = RegexBuilder.from_regex(source)
+    reversed_compiled = reversed_builder.to_regex()
+    for candidate in ["", "a", "abc", "abc123", "xyz", "foo bar", "hi"]:
+        assert bool(original.search(candidate)) == bool(reversed_compiled.search(candidate))
+
+
+def test_from_regex_raises_for_unsupported_construct():
+    with pytest.raises(UnsupportedReverseParseError):
+        RegexBuilder.from_regex(r"(a)\1")
+
+
+def test_from_regex_raises_for_alternation_with_non_literal_branch():
+    with pytest.raises(UnsupportedReverseParseError):
+        RegexBuilder.from_regex(r"a|\d+")
+
+
+def test_from_regex_raises_for_unsupported_class_member_shape():
+    with pytest.raises(UnsupportedReverseParseError):
+        RegexBuilder.from_regex(r"[\da-z_]")
+
+
+def test_from_regex_lazy_quantifier_translates_via_lazy_variants():
+    builder = RegexBuilder.from_regex(r"a+?")
+    assert builder.to_regex_string() == "a+?"
+
+
+def test_from_regex_lazy_between_translates_via_lazy_variant():
+    builder = RegexBuilder.from_regex(r"a{2,5}?")
+    assert builder.to_regex_string() == "a{2,5}?"
+
+
+def test_from_regex_lazy_zero_or_more_translates_via_lazy_variant():
+    builder = RegexBuilder.from_regex(r"a*?")
+    assert builder.to_regex_string() == "a*?"
+
+
+def test_from_regex_named_group_reproduces_the_name():
+    builder = RegexBuilder.from_regex("(?P<username>[a-z]+)")
+    emitted = builder.to_regex_string()
+    assert emitted == "(?P<username>[a-z]+)"
+
+
+def test_unsupported_error_message_names_the_offending_construct():
+    with pytest.raises(UnsupportedReverseParseError) as excinfo:
+        RegexBuilder.from_regex(r"(a)\1")
+    assert "hand-write" in str(excinfo.value)
+
+
+def test_from_regex_produces_a_regexbuilder_not_a_pattern():
+    builder = RegexBuilder.from_regex("abc")
+    assert isinstance(builder, RegexBuilder)
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