fix: respect `--prerelease` in the install script

README.md

@@ -92,7 +92,7 @@ curl -sSL https://raw.githubusercontent.com/pdm-project/pdm/main/install-pdm.py
 ```
 
 For security reasons, you should verify the checksum of `install-pdm.py`.
-The sha256 checksum is: `5efebd44f477521d0d8ef0e118b7e5765ff20f80d3d4dd9394f1b8ff1094fb4d`
+The sha256 checksum is: `f09accb8a530315be312cf9ce7af987ccb608aa90d3972968d73e7ef7d8c547b`
 
 The installer will install PDM into the user site and the location depends on the system:
 

README_zh.md

@@ -87,7 +87,7 @@ curl -sSL https://raw.githubusercontent.com/pdm-project/pdm/main/install-pdm.py
 ```
 
 为安全起见，你应该检查 `install-pdm.py` 文件的正确性。
-SHA256 校验和: `5efebd44f477521d0d8ef0e118b7e5765ff20f80d3d4dd9394f1b8ff1094fb4d`
+SHA256 校验和: `f09accb8a530315be312cf9ce7af987ccb608aa90d3972968d73e7ef7d8c547b`
 
 默认情况下，此脚本会将 PDM 安装在 Python 的用户目录下，具体位置取决于当前系统：
 

docs/docs/index.md

@@ -50,7 +50,7 @@ Like Pip, PDM provides an installation script that will install PDM into an isol
     ```
 
 For security reasons, you should verify the checksum of `install-pdm.py`.
-The sha256 checksum is: `5efebd44f477521d0d8ef0e118b7e5765ff20f80d3d4dd9394f1b8ff1094fb4d`
+The sha256 checksum is: `f09accb8a530315be312cf9ce7af987ccb608aa90d3972968d73e7ef7d8c547b`
 
 The installer will install PDM into the user site and the location depends on the system:
 

install-pdm.py

@@ -6,6 +6,7 @@ import io
 import json
 import os
 import platform
+import re
 import shutil
 import site
 import subprocess
@@ -207,14 +208,23 @@ class Installer:
         resp = urllib.request.urlopen(JSON_URL)
         metadata = json.load(resp)
 
-        def is_stable(v: str) -> bool:
-            return all(p.isdigit() for p in v.split("."))
+        def version_okay(v: str) -> bool:
+            return self.prerelease or all(p.isdigit() for p in v.split("."))
 
         def sort_version(v: str) -> tuple:
-            return tuple(int(p) for p in v.split("."))
+            parts = []
+            for part in v.split("."):
+                if part.isdigit():
+                    parts.append(int(part))
+                else:
+                    digit, rest = re.match(r"^(\d*)(.*)", part).groups()
+                    if digit:
+                        parts.append(int(digit))
+                    parts.append(rest)
+            return tuple(parts)
 
         releases = sorted(
-            filter(is_stable, metadata["releases"]), key=sort_version, reverse=True
+            filter(version_okay, metadata["releases"]), key=sort_version, reverse=True
         )
 
         return releases[0]
@@ -300,8 +310,6 @@ class Installer:
         else:
             req = "pdm"
         args = [req] + [d for d in self.additional_deps if d]
-        if self.prerelease:
-            args.insert(0, "--pre")
         pip_cmd = [str(venv_python), "-m", "pip", "install"] + args
         _call_subprocess(pip_cmd)