From f0e2e86ae2cde73bcf82fbd62396c6849365273e Mon Sep 17 00:00:00 2001
From: Isaac Corbrey <isaac@isaaccorbrey.com>
Date: Sat, 13 Jun 2026 09:34:41 -0500
Subject: [PATCH] jujutsu: Fix rustfmt fix tool

---
 modules/home/jujutsu/default.nix        | 17 ++++-
 modules/home/jujutsu/rustfmt-wrapper.sh | 86 +++++++++++++++++++++++++
 2 files changed, 102 insertions(+), 1 deletion(-)
 create mode 100755 modules/home/jujutsu/rustfmt-wrapper.sh

diff --git a/modules/home/jujutsu/default.nix b/modules/home/jujutsu/default.nix
index 69c4966..edb043f 100644
--- a/modules/home/jujutsu/default.nix
+++ b/modules/home/jujutsu/default.nix
@@ -177,9 +177,24 @@
         ];
       }
       (lib.mkIf config.modules.home.rust.enable {
+        # `jj fix` pipes content via stdin, leaving rustfmt unable to walk
+        # upward to find Cargo.toml and read the workspace's edition. The
+        # wrapper takes `$root`/`$path` from jj's substitution, resolves
+        # the file's enclosing crate (handling workspace inheritance via
+        # `[workspace.package].edition`), and invokes rustfmt with
+        # `--edition` set correctly per file.
+        home.file.".config/jj/scripts/rustfmt-wrapper.sh" = {
+          source = ./rustfmt-wrapper.sh;
+          executable = true;
+        };
+
         programs.jujutsu.settings = {
           fix.tools.rustfmt = {
-            command = ["rustfmt" "--emit" "stdout"];
+            command = [
+              "${config.home.homeDirectory}/.config/jj/scripts/rustfmt-wrapper.sh"
+              "$root"
+              "$path"
+            ];
             patterns = ["glob:'**/*.rs'"];
           };
         };
diff --git a/modules/home/jujutsu/rustfmt-wrapper.sh b/modules/home/jujutsu/rustfmt-wrapper.sh
new file mode 100755
index 0000000..02c13a2
--- /dev/null
+++ b/modules/home/jujutsu/rustfmt-wrapper.sh
@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+# rustfmt-wrapper: invoke rustfmt with the correct Rust edition for the
+# file being formatted.
+#
+# `jj fix` pipes file content via stdin; without a file path, rustfmt
+# can't walk upward to find Cargo.toml on its own, so it defaults to
+# Rust 2015 and rejects every `async fn` in a modern crate. This
+# wrapper takes the workspace root and repo-relative path as arguments
+# (jj's `$root` and `$path` substitutions), walks upward from the
+# resolved file to find the nearest Cargo.toml with an edition
+# declaration, and invokes rustfmt with `--edition` explicit.
+#
+# Falls back to edition 2021 if no Cargo.toml is found or the edition
+# can't be parsed — 2021 is the most common modern edition and is a
+# strict subset of 2024, so misclassification just means slightly
+# older formatting rules, never a syntax-rejection.
+#
+# Workspace inheritance is handled: a member crate that uses
+# `edition.workspace = true` causes the walk to continue upward
+# until the workspace root's `[workspace.package].edition` is found.
+
+set -euo pipefail
+
+workspace_root="${1:-}"
+repo_path="${2:-}"
+fallback_edition="2021"
+
+# Extract a TOML string value for `key` inside [`section`] of `manifest`.
+# Looks for `key = "value"` on its own line within the named section.
+# Doesn't handle inline tables or multiline strings — neither of which
+# Cargo's edition field uses in practice.
+read_toml_string() {
+  local manifest="$1"
+  local section="$2"
+  local key="$3"
+  awk -v want_section="[${section}]" -v key="${key}" '
+    /^\[/ { current = $0; next }
+    current == want_section {
+      if (match($0, "^[[:space:]]*" key "[[:space:]]*=[[:space:]]*\"")) {
+        sub(/^[^"]*"/, "")
+        sub(/".*$/, "")
+        print
+        exit
+      }
+    }
+  ' "$manifest"
+}
+
+find_edition() {
+  local start_dir="$1"
+  local dir="$start_dir"
+
+  while [[ -n "$dir" && "$dir" != "/" ]]; do
+    local cargo="${dir}/Cargo.toml"
+    if [[ -f "$cargo" ]]; then
+      # [package].edition: the common per-crate case.
+      local found
+      found="$(read_toml_string "$cargo" "package" "edition")"
+      if [[ -n "$found" ]]; then
+        printf '%s\n' "$found"
+        return 0
+      fi
+      # [workspace.package].edition: the inherited-from-workspace case.
+      found="$(read_toml_string "$cargo" "workspace.package" "edition")"
+      if [[ -n "$found" ]]; then
+        printf '%s\n' "$found"
+        return 0
+      fi
+    fi
+    dir="$(dirname "$dir")"
+  done
+
+  return 1
+}
+
+edition="$fallback_edition"
+
+if [[ -n "$workspace_root" && -n "$repo_path" ]]; then
+  abs_path="${workspace_root}/${repo_path}"
+  start_dir="$(dirname "$abs_path")"
+  if detected="$(find_edition "$start_dir" 2>/dev/null)"; then
+    edition="$detected"
+  fi
+fi
+
+exec rustfmt --emit stdout --edition "$edition"
-- 
2.51.2