Avoid recreating unchanged global aliases, and use hard links where possible

src/manage/commands.py

@@ -351,6 +351,10 @@ class BaseCommand:
     show_help = False
 
     def __init__(self, args, root=None):
+        # Storage for command-specific data per-command execution.
+        # All data should use a unique key.
+        self.scratch = {}
+
         cmd_args = {
             k: v for k, v in
             [*CLI_SCHEMA.items(), *CLI_SCHEMA.get(self.CMD, {}).items()]

src/manage/install_command.py

@@ -223,13 +223,14 @@ def _if_exists(launcher, plat):
     return launcher
 
 
-def _write_alias(cmd, install, alias, target):
+def _write_alias(cmd, install, alias, target, _link=os.link):
     p = (cmd.global_dir / alias["name"])
+    target = Path(target)
     ensure_tree(p)
-    unlink(p)
     launcher = cmd.launcher_exe
     if alias.get("windowed"):
         launcher = cmd.launcherw_exe or launcher
+
     plat = install["tag"].rpartition("-")[-1]
     if plat:
         LOGGER.debug("Checking for launcher for platform -%s", plat)
@@ -247,8 +248,71 @@ def _write_alias(cmd, install, alias, target):
         else:
             LOGGER.debug("Skipping %s alias because the launcher template was not found.", alias["name"])
         return
-    p.write_bytes(launcher.read_bytes())
-    p.with_name(p.name + ".__target__").write_text(str(target), encoding="utf-8")
+
+    try:
+        launcher_bytes = launcher.read_bytes()
+    except OSError:
+        warnings_shown = cmd.scratch.setdefault("install_command._write_alias.warnings_shown", set())
+        if str(launcher) not in warnings_shown:
+            LOGGER.warn("Failed to read launcher template at %s.", launcher)
+            warnings_shown.add(str(launcher))
+        LOGGER.debug("Failed to read %s", launcher, exc_info=True)
+        return
+
+    existing_bytes = b''
+    try:
+        with open(p, 'rb') as f:
+            existing_bytes = f.read(len(launcher_bytes) + 1)
+    except FileNotFoundError:
+        pass
+    except OSError:
+        LOGGER.debug("Failed to read existing alias launcher.")
+
+    launcher_remap = cmd.scratch.setdefault("install_command._write_alias.launcher_remap", {})
+
+    if existing_bytes == launcher_bytes:
+        # Valid existing launcher, so save its path in case we need it later
+        # for a hard link.
+        launcher_remap.setdefault(launcher.name, p)
+    else:
+        # First try and create a hard link
+        unlink(p)
+        try:
+            _link(launcher, p)
+            LOGGER.debug("Created %s as hard link to %s", p.name, launcher.name)
+        except OSError as ex:
+            if ex.winerror != 17:
+                # Report errors other than cross-drive links
+                LOGGER.debug("Failed to create hard link for command.", exc_info=True)
+            launcher2 = launcher_remap.get(launcher.name)
+            if launcher2:
+                try:
+                    _link(launcher2, p)
+                    LOGGER.debug("Created %s as hard link to %s", p.name, launcher2.name)
+                except FileNotFoundError:
+                    raise
+                except OSError:
+                    LOGGER.debug("Failed to create hard link to fallback launcher")
+                    launcher2 = None
+            if not launcher2:
+                try:
+                    p.write_bytes(launcher_bytes)
+                    LOGGER.debug("Created %s as copy of %s", p.name, launcher.name)
+                    launcher_remap[launcher.name] = p
+                except OSError:
+                    LOGGER.error("Failed to create global command %s.", alias["name"])
+                    LOGGER.debug(exc_info=True)
+
+    p_target = p.with_name(p.name + ".__target__")
+    try:
+        if target.match(p_target.read_text(encoding="utf-8")):
+            return
+    except FileNotFoundError:
+        pass
+    except (OSError, UnicodeDecodeError):
+        LOGGER.debug("Failed to read existing target path.", exc_info=True)
+
+    p_target.write_text(str(target), encoding="utf-8")
 
 
 def _create_shortcut_pep514(cmd, install, shortcut):

tests/test_install_command.py

@@ -22,6 +22,7 @@ class Cmd:
         default_platform = "-64"
 
         def __init__(self, platform=None):
+            self.scratch = {}
             if platform:
                 self.default_platform = platform
 
@@ -81,19 +82,19 @@ def check_warm64(self, cmd, tag, name):
 
 
 def test_write_alias_tag_with_platform(alias_checker):
-    alias_checker.check_32(alias_checker.Cmd, "1.0-32", "testA")
-    alias_checker.check_w32(alias_checker.Cmd, "1.0-32", "testB")
-    alias_checker.check_64(alias_checker.Cmd, "1.0-64", "testC")
-    alias_checker.check_w64(alias_checker.Cmd, "1.0-64", "testD")
-    alias_checker.check_arm64(alias_checker.Cmd, "1.0-arm64", "testE")
-    alias_checker.check_warm64(alias_checker.Cmd, "1.0-arm64", "testF")
+    alias_checker.check_32(alias_checker.Cmd(), "1.0-32", "testA")
+    alias_checker.check_w32(alias_checker.Cmd(), "1.0-32", "testB")
+    alias_checker.check_64(alias_checker.Cmd(), "1.0-64", "testC")
+    alias_checker.check_w64(alias_checker.Cmd(), "1.0-64", "testD")
+    alias_checker.check_arm64(alias_checker.Cmd(), "1.0-arm64", "testE")
+    alias_checker.check_warm64(alias_checker.Cmd(), "1.0-arm64", "testF")
 
 
 def test_write_alias_default_platform(alias_checker):
     alias_checker.check_32(alias_checker.Cmd("-32"), "1.0", "testA")
     alias_checker.check_w32(alias_checker.Cmd("-32"), "1.0", "testB")
-    alias_checker.check_64(alias_checker.Cmd, "1.0", "testC")
-    alias_checker.check_w64(alias_checker.Cmd, "1.0", "testD")
+    alias_checker.check_64(alias_checker.Cmd(), "1.0", "testC")
+    alias_checker.check_w64(alias_checker.Cmd(), "1.0", "testD")
     alias_checker.check_arm64(alias_checker.Cmd("-arm64"), "1.0", "testE")
     alias_checker.check_warm64(alias_checker.Cmd("-arm64"), "1.0", "testF")
 
@@ -103,13 +104,128 @@ def test_write_alias_fallback_platform(alias_checker):
     alias_checker.check_w64(alias_checker.Cmd("-spam"), "1.0", "testB")
 
 
+def test_write_alias_launcher_missing(fake_config, assert_log, tmp_path):
+    fake_config.launcher_exe = tmp_path / "non-existent.exe"
+    fake_config.default_platform = '-32'
+    fake_config.global_dir = tmp_path / "bin"
+    IC._write_alias(
+        fake_config,
+        {"tag": "test"},
+        {"name": "test.exe"},
+        tmp_path / "target.exe",
+    )
+    assert_log(
+        "Checking for launcher.*",
+        "Checking for launcher.*",
+        "Checking for launcher.*",
+        "Create %s linking to %s",
+        "Skipping %s alias because the launcher template was not found.",
+        assert_log.end_of_log(),
+    )
+
+
+def test_write_alias_launcher_unreadable(fake_config, assert_log, tmp_path):
+    class FakeLauncherPath:
+        stem = "test"
+        suffix = ".exe"
+        parent = tmp_path
+
+        @staticmethod
+        def is_file():
+            return True
+
+        @staticmethod
+        def read_bytes():
+            raise OSError("no reading for the test")
+
+    fake_config.scratch = {}
+    fake_config.launcher_exe = FakeLauncherPath
+    fake_config.default_platform = '-32'
+    fake_config.global_dir = tmp_path / "bin"
+    IC._write_alias(
+        fake_config,
+        {"tag": "test"},
+        {"name": "test.exe"},
+        tmp_path / "target.exe",
+    )
+    assert_log(
+        "Checking for launcher.*",
+        "Create %s linking to %s",
+        "Failed to read launcher template at %s\\.",
+        "Failed to read %s",
+        assert_log.end_of_log(),
+    )
+
+
+def test_write_alias_launcher_unlinkable(fake_config, assert_log, tmp_path):
+    def fake_link(x, y):
+        raise OSError("Error for testing")
+
+    fake_config.scratch = {}
+    fake_config.launcher_exe = tmp_path / "launcher.txt"
+    fake_config.launcher_exe.write_bytes(b'Arbitrary contents')
+    fake_config.default_platform = '-32'
+    fake_config.global_dir = tmp_path / "bin"
+    IC._write_alias(
+        fake_config,
+        {"tag": "test"},
+        {"name": "test.exe"},
+        tmp_path / "target.exe",
+        _link=fake_link
+    )
+    assert_log(
+        "Checking for launcher.*",
+        "Create %s linking to %s",
+        "Failed to create hard link.+",
+        "Created %s as copy of %s",
+        assert_log.end_of_log(),
+    )
+
+
+def test_write_alias_launcher_unlinkable_remap(fake_config, assert_log, tmp_path):
+    # This is for the fairly expected case of the PyManager install being on one
+    # drive, but the global commands directory being on another. In this
+    # situation, we can't hard link directly into the app files, and will need
+    # to copy. But we only need to copy once, so if a launcher_remap has been
+    # set (in the current process), then we have an available copy already and
+    # can link to that.
+
+    def fake_link(x, y):
+        if x.match("launcher.txt"):
+            raise OSError(17, "Error for testing")
+
+    fake_config.scratch = {
+        "install_command._write_alias.launcher_remap": {"launcher.txt": tmp_path / "actual_launcher.txt"},
+    }
+    fake_config.launcher_exe = tmp_path / "launcher.txt"
+    fake_config.launcher_exe.write_bytes(b'Arbitrary contents')
+    (tmp_path / "actual_launcher.txt").write_bytes(b'Arbitrary contents')
+    fake_config.default_platform = '-32'
+    fake_config.global_dir = tmp_path / "bin"
+    IC._write_alias(
+        fake_config,
+        {"tag": "test"},
+        {"name": "test.exe"},
+        tmp_path / "target.exe",
+        _link=fake_link
+    )
+    assert_log(
+        "Checking for launcher.*",
+        "Create %s linking to %s",
+        "Failed to create hard link.+",
+        ("Created %s as hard link to %s", ("test.exe", "actual_launcher.txt")),
+        assert_log.end_of_log(),
+    )
+
+
 @pytest.mark.parametrize("default", [1, 0])
 def test_write_alias_default(alias_checker, monkeypatch, tmp_path, default):
     prefix = Path(tmp_path) / "runtime"
 
     class Cmd:
         global_dir = Path(tmp_path) / "bin"
         launcher_exe = None
+        scratch = {}
         def get_installs(self):
             return [
                 {
@@ -146,6 +262,7 @@ def write_alias(*a):
 
 def test_print_cli_shortcuts(patched_installs, assert_log, monkeypatch, tmp_path):
     class Cmd:
+        scratch = {}
         global_dir = Path(tmp_path)
         def get_installs(self):
             return installs.get_installs(None)
@@ -163,6 +280,7 @@ def get_installs(self):
 
 def test_print_path_warning(patched_installs, assert_log, tmp_path):
     class Cmd:
+        scratch = {}
         global_dir = Path(tmp_path)
         def get_installs(self):
             return installs.get_installs(None)