fix(install): upgrading from a beta to its own release was refused

Hit it updating the test box from v1.6.0-beta.3 to v1.6.0: the installer
called it a downgrade and aborted.

`sort -V` is not semver aware. It reads `1.6.0-beta.3` as `1.6.0` plus extra
characters and sorts it AFTER the finished release, so the guard that exists
to stop an accidental rollback fired on the single most common upgrade there
is — every beta tester moving to the version they were testing.

The prerelease separator is swapped for `~` before comparing. That is the one
character version sort orders before end-of-string, which is exactly the
semver rule that a prerelease precedes the version it leads to.

Tested against the comparison lifted out of install.sh itself rather than a
retyped copy — a test agreeing with a paraphrase would have passed while the
shipped code was wrong.

Author: DaveBugg

backend/tests/test_install_script.py

@@ -0,0 +1,80 @@
+"""Unit tests for `install.sh`.
+
+The installer is not sourceable — it runs top to bottom — so the version
+comparison is lifted out of the file itself and evaluated, rather than a copy
+of it being retyped here. A test that agrees with a paraphrase of the code
+would have passed while the shipped comparison was wrong.
+"""
+import os
+import re
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+INSTALL_SH = Path(__file__).resolve().parents[2] / "install.sh"
+BASH = shutil.which("bash")
+
+pytestmark = pytest.mark.skipif(
+    BASH is None or not INSTALL_SH.exists(), reason="bash or install.sh unavailable",
+)
+
+
+def _comparison_lines() -> str:
+    """The lines install.sh uses to decide 'is the target older?'."""
+    text = INSTALL_SH.read_text(encoding="utf-8", errors="ignore")
+    wanted = [
+        ln.strip() for ln in text.splitlines()
+        if re.match(r'^\s*_(running|target)_cmp=', ln)
+    ]
+    assert wanted, "install.sh no longer prepares comparable version strings"
+    return "\n".join(wanted)
+
+
+def is_downgrade(running: str, target: str) -> bool:
+    """Run the installer's own comparison for one pair of versions."""
+    body = f"""
+_running_num="{running}"
+_target_num="{target}"
+{_comparison_lines()}
+if [[ "$_running_num" != "$_target_num" \\
+      && "$(printf '%s\\n%s\\n' "$_running_cmp" "$_target_cmp" | sort -V | tail -1)" == "$_running_cmp" ]]; then
+    echo DOWNGRADE
+else
+    echo OK
+fi
+"""
+    r = subprocess.run([BASH, "-c", body], capture_output=True, text=True,
+                       env=dict(os.environ), timeout=30)
+    assert r.returncode == 0, r.stderr
+    return r.stdout.strip() == "DOWNGRADE"
+
+
+class TestDowngradeDetection:
+    def test_beta_to_its_own_release_is_an_upgrade(self):
+        """The single most common upgrade there is, and it was refused:
+        `sort -V` is not semver aware — it reads `1.6.0-beta.3` as `1.6.0`
+        plus extra characters and sorts it AFTER the finished release."""
+        assert not is_downgrade("1.6.0-beta.3", "1.6.0")
+        assert not is_downgrade("1.6.0-beta.1", "1.6.0")
+
+    def test_release_to_its_own_beta_is_a_downgrade(self):
+        assert is_downgrade("1.6.0", "1.6.0-beta.3")
+
+    def test_ordinary_upgrades_are_allowed(self):
+        assert not is_downgrade("1.5.3", "1.6.0")
+        assert not is_downgrade("1.6.0", "1.6.1")
+        assert not is_downgrade("1.6.0", "2.0.0")
+
+    def test_ordinary_downgrades_are_caught(self):
+        assert is_downgrade("1.6.0", "1.5.3")
+        assert is_downgrade("1.6.1", "1.6.0")
+
+    def test_betas_are_ordered_among_themselves(self):
+        assert not is_downgrade("1.6.0-beta.2", "1.6.0-beta.3")
+        assert is_downgrade("1.6.0-beta.3", "1.6.0-beta.2")
+
+    def test_the_same_version_is_neither(self):
+        assert not is_downgrade("1.6.0", "1.6.0")
+        assert not is_downgrade("1.6.0-beta.3", "1.6.0-beta.3")

install.sh

@@ -573,12 +573,22 @@ fi
 # Use `sort -V` (version sort) as a cheap semver comparator. Strips a
 # leading `v`, then asks whether running > resolved. If yes, abort.
 # Same-version (running == resolved) handled separately below.
+#
+# The prerelease separator is swapped for `~` first. `sort -V` is not semver
+# aware: it reads `1.6.0-beta.3` as `1.6.0` plus extra characters and sorts it
+# AFTER the finished release, so upgrading from any beta to the release it was
+# a beta of looked like a downgrade and was refused — which is the single most
+# common upgrade there is. `~` is the one character version sort orders before
+# end-of-string, which is exactly the semver rule that a prerelease precedes
+# the version it leads to.
 if [[ "$IS_UPDATE" == "1" \
       && -n "$RUNNING_VERSION" && "$RUNNING_VERSION" != "?" ]]; then
     _running_num="${RUNNING_VERSION#v}"
     _target_num="${DISPLAY_VERSION#v}"
+    _running_cmp="${_running_num/-/\~}"
+    _target_cmp="${_target_num/-/\~}"
     if [[ "$_running_num" != "$_target_num" \
-          && "$(printf '%s\n%s\n' "$_running_num" "$_target_num" | sort -V | tail -1)" == "$_running_num" ]]; then
+          && "$(printf '%s\n%s\n' "$_running_cmp" "$_target_cmp" | sort -V | tail -1)" == "$_running_cmp" ]]; then
         echo ""
         warn "════════════════════════════════════════════════════════════════════"
         warn "  ⛔ DOWNGRADE DETECTED — aborting."