Show progress while nh clean collects garbage

bin/nh.py

@@ -0,0 +1,83 @@
+import os
+import re
+import subprocess
+import sys
+import time
+from typing import TextIO
+
+# Nix prints one of these per store path it deletes. `nh clean` shells out to
+# `nix store gc`, which drops its verbosity to `lvlNotice` whenever it thinks
+# it is attached to a terminal, so these lines only exist because this wrapper
+# puts a pipe on nh's stdout:
+# https://github.com/NixOS/nix/blob/master/src/nix/main.cc#L435-L441
+deleting = re.compile(r"^deleting '/nix/store/[^']*'$")
+
+# Global nh options that take a separate value, which we skip over while
+# looking for the subcommand:
+# https://github.com/nix-community/nh/blob/master/crates/nh/src/interface.rs
+takes_value = {"-e", "--elevation-strategy", "--elevation-program"}
+
+
+def subcommand(args: list[str]) -> str | None:
+    rest = iter(args)
+    for arg in rest:
+        if arg in takes_value:
+            next(rest, None)
+        elif not arg.startswith("-"):
+            return arg
+    return None
+
+
+def summarize(stdout: TextIO) -> None:
+    count = 0
+    start = None
+    while line := stdout.readline():
+        line = line.rstrip("\n")
+        if deleting.match(line):
+            if start is None:
+                start = time.monotonic()
+            count += 1
+            elapsed = int(time.monotonic() - start)
+            minutes, seconds = divmod(elapsed, 60)
+            status = f"  {count:,} paths deleted ({minutes}m{seconds:02d}s)"
+            print(f"\033[2K\r{status}", end="", flush=True)
+        else:
+            if start is not None:
+                print()
+                start = None
+            print(line, flush=True)
+    if start is not None:
+        print()
+
+
+def main() -> None:
+    args = sys.argv[1:]
+    # Only `nh clean` sits silent for minutes on end; leave everything else
+    # (notably the nom output of `nh os`) exactly as it is. `--ask` wants a
+    # terminal for its prompt, and a redirected stdout deserves the unabridged
+    # log rather than a status line that redraws itself.
+    if (
+        subcommand(args) != "clean"
+        or "--ask" in args
+        or not sys.stdout.isatty()
+    ):
+        os.execvp("nh", ["nh", *args])
+    # Only stdout is piped: nh merges the stderr of `nix store gc` into its own
+    # stdout, so that is where the interesting lines land, and nh's own logging
+    # on stderr reaches the terminal untouched.
+    with subprocess.Popen(
+        ["nh", *args],
+        stdout=subprocess.PIPE,
+        text=True,
+        errors="replace",
+    ) as process:
+        assert process.stdout is not None
+        try:
+            summarize(process.stdout)
+        except KeyboardInterrupt:
+            print()
+    sys.exit(process.returncode)
+
+
+if __name__ == "__main__":
+    main()

modules/base.nix

@@ -23,7 +23,6 @@ in
     pkgs.cloc
     pkgs.comma
     pkgs.git
-    pkgs.nh # https://github.com/nix-community/nix-index/issues/317
     pkgs.nixfmt
     pkgs.npc
     pkgs.npb
@@ -43,6 +42,17 @@ in
         (pkgs.writers.writePython3Bin "doing" { } ../bin/doing.py)
         (pkgs.writers.writePython3Bin "flake" { } ../bin/flake.py)
         (pkgs.writers.writePython3Bin "ghcode" { } ../bin/ghcode.py)
+        # https://github.com/nix-community/nix-index/issues/317
+        # The wrapper gives `nh clean` a progress line while it collects
+        # garbage; the PATH prefix is what `nh` resolves to inside it.
+        (pkgs.writers.writePython3Bin "nh" {
+          makeWrapperArgs = [
+            "--prefix"
+            "PATH"
+            ":"
+            (lib.makeBinPath [ pkgs.nh ])
+          ];
+        } ../bin/nh.py)
         (pkgs.writers.writePython3Bin "scratch" { } ../bin/scratch.py)
         (pkgs.writers.writePython3Bin "shell" { } ../bin/shell.py)
         (pkgs.writers.writePython3Bin "title" { } ../bin/title.py)