From 0392d4b9697255176073faceb2299dbe92d7b1d3 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Thu, 24 Sep 2026 16:36:17 +0100
Subject: [PATCH] Use resolved scheme for emptiness check in ToVersString

ToVersString resolved its scheme argument but then called r.IsEmpty(),
which re-read r.Scheme. A schemeless Range from NewRange with PyPI
intervals was judged empty under the generic comparator and serialised
as vers:pypi/.

Fixes #52.
---
 parser.go      |  2 +-
 parser_test.go | 18 ++++++++++++++++++
 range.go       |  6 +++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/parser.go b/parser.go
index af0ecf1..ca9e2d4 100644
--- a/parser.go
+++ b/parser.go
@@ -182,7 +182,7 @@ func (p *Parser) ToVersString(r *Range, scheme string) string {
 		return fmt.Sprintf("vers:%s/*", scheme)
 	}
 	// Check if empty but has raw constraints (preserve them for output)
-	if r.IsEmpty() && len(r.RawConstraints) == 0 {
+	if r.isEmptyFor(scheme) && len(r.RawConstraints) == 0 {
 		return fmt.Sprintf("vers:%s/", scheme)
 	}
 
diff --git a/parser_test.go b/parser_test.go
index 3923688..53b280c 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -536,6 +536,24 @@ func TestToVersString(t *testing.T) {
 			"npm",
 			"vers:npm/>=1.0.0|<2.0.0",
 		},
+		{
+			"schemeless pypi calver range",
+			NewRange([]Interval{NewInterval("2016.11.0", "3003rc1", true, false)}),
+			"pypi",
+			"vers:pypi/>=2016.11.0|<3003rc1",
+		},
+		{
+			"schemeless pypi dev range",
+			NewRange([]Interval{NewInterval("0.5.0b3.dev13", "0.5.0b3.dev97", true, false)}),
+			"pypi",
+			"vers:pypi/>=0.5.0b3.dev13|<0.5.0b3.dev97",
+		},
+		{
+			"schemeless empty interval",
+			NewRange([]Interval{NewInterval("2.0", "1.0", true, false)}),
+			"pypi",
+			"vers:pypi/",
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/range.go b/range.go
index 841509b..a48127e 100644
--- a/range.go
+++ b/range.go
@@ -180,10 +180,14 @@ func samePEP440Release(left, right pep440Version) bool {
 
 // IsEmpty returns true if this range matches no versions.
 func (r *Range) IsEmpty() bool {
+	return r.isEmptyFor(r.Scheme)
+}
+
+func (r *Range) isEmptyFor(scheme string) bool {
 	if len(r.Intervals) == 0 {
 		return true
 	}
-	cmp := compareFuncFor(r.Scheme)
+	cmp := compareFuncFor(scheme)
 	for _, interval := range r.Intervals {
 		if !interval.isEmptyCmp(cmp) {
 			return false