From f12880688dad3dd9ac561927a765038d1c0990d4 Mon Sep 17 00:00:00 2001
From: Ophestra <cat@gensokyo.uk>
Date: Sat, 2 May 2026 02:08:25 +0900
Subject: [PATCH] internal/rosa/gnu: test skip helper

The terribleness of GNU invites interesting helpers.

Signed-off-by: Ophestra <cat@gensokyo.uk>
---
 internal/rosa/gnu.go      | 37 +++++++++++++++++++++++++++++++++++++
 internal/rosa/gnu_test.go | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 internal/rosa/gnu_test.go

diff --git a/internal/rosa/gnu.go b/internal/rosa/gnu.go
index c568bbdc..0a944d6a 100644
--- a/internal/rosa/gnu.go
+++ b/internal/rosa/gnu.go
@@ -2,10 +2,47 @@ package rosa
 
 import (
 	"runtime"
+	"slices"
+	"strconv"
+	"strings"
 
 	"hakurei.app/internal/pkg"
 )
 
+// skipGNUTests generates a string for skipping specific tests by number in a
+// GNU test suite. This is nontrivial because the test suite does not support
+// excluding tests in any way, so ranges for all but the skipped tests have to
+// be specified instead.
+//
+// For example, to skip test 764, ranges around the skipped test must be
+// specified:
+//
+//	1-763 765-
+//
+// Tests are numbered starting from 1. The resulting string is unquoted.
+func skipGNUTests(tests ...int) string {
+	tests = slices.Clone(tests)
+	slices.Sort(tests)
+
+	var buf strings.Builder
+
+	if tests[0] != 1 {
+		buf.WriteString("1-")
+	}
+
+	for i, n := range tests {
+		if n != 1 && (i == 0 || tests[i-1] != n-1) {
+			buf.WriteString(strconv.Itoa(n - 1))
+			buf.WriteString(" ")
+		}
+		if i == len(tests)-1 || tests[i+1] != n+1 {
+			buf.WriteString(strconv.Itoa(n + 1))
+			buf.WriteString("-")
+		}
+	}
+	return buf.String()
+}
+
 func (t Toolchain) newM4() (pkg.Artifact, string) {
 	const (
 		version  = "1.4.21"
diff --git a/internal/rosa/gnu_test.go b/internal/rosa/gnu_test.go
new file mode 100644
index 00000000..94d82618
--- /dev/null
+++ b/internal/rosa/gnu_test.go
@@ -0,0 +1,35 @@
+package rosa
+
+import (
+	"slices"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestSkipGNUTests(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		tests []int
+		want  string
+	}{
+		{[]int{764}, "1-763 765-"},
+		{[]int{764, 0xcafe, 37, 9}, "1-8 10-36 38-763 765-51965 51967-"},
+		{[]int{1, 2, 0xbed}, "3-3052 3054-"},
+		{[]int{3, 4}, "1-2 5-"},
+	}
+	for _, tc := range testCases {
+		t.Run(strings.Join(slices.Collect(func(yield func(string) bool) {
+			for _, n := range tc.tests {
+				yield(strconv.Itoa(n))
+			}
+		}), ","), func(t *testing.T) {
+			t.Parallel()
+
+			if got := skipGNUTests(tc.tests...); got != tc.want {
+				t.Errorf("skipGNUTests: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}