Add conformance tests, fix log sort order and --stat passthrough

- tests/conformance.sh: 14 tests comparing nit output against git on a
  controlled repo. Covers status, log, diff (unstaged + staged), show,
  show --stat, and passthrough (branch, --graph, --name-only, --stat).
- Fix log sort: use TOPOLOGICAL | TIME (was TIME only), which caused
  wrong commit order on repos with close timestamps.
- Fix --stat passthrough: only treat --stat as a known flag for the show
  command. Previously 'nit diff --stat' ran nit's diff (ignoring --stat)
  instead of passing through to git.
- Parse command before flags so flag validity is context-aware.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fielding

src/cli.zig

@@ -37,6 +37,8 @@ pub fn run() !void {
         return;
     }
 
+    const cmd = args[1];
+
     var human = false;
     var count: usize = 20;
     var staged = false;
@@ -48,7 +50,7 @@ pub fn run() !void {
             human = true;
         } else if (std.mem.eql(u8, arg, "-s") or std.mem.eql(u8, arg, "--staged")) {
             staged = true;
-        } else if (std.mem.eql(u8, arg, "--stat")) {
+        } else if (std.mem.eql(u8, arg, "--stat") and std.mem.eql(u8, cmd, "show")) {
             stat = true;
         } else if (std.mem.eql(u8, arg, "-n")) {
             // Handled below with value parsing
@@ -72,8 +74,6 @@ pub fn run() !void {
         return passthrough(args);
     }
 
-    const cmd = args[1];
-
     // Passthrough and help skip libgit2 entirely for faster startup
     if (std.mem.eql(u8, cmd, "help") or std.mem.eql(u8, cmd, "-h") or std.mem.eql(u8, cmd, "--help")) {
         try w.writeAll(usage);

src/cmd/log.zig

@@ -12,7 +12,7 @@ pub fn run(repo: *c.git_repository, human: bool, count: usize, w: *Writer) !void
     defer c.git_revwalk_free(walk);
 
     try git.check(c.git_revwalk_push_head(walk));
-    _ = c.git_revwalk_sorting(walk, c.GIT_SORT_TIME);
+    _ = c.git_revwalk_sorting(walk, c.GIT_SORT_TIME | c.GIT_SORT_TOPOLOGICAL);
 
     var oid: c.git_oid = undefined;
     var shown: usize = 0;

tests/conformance.sh

@@ -0,0 +1,232 @@
+#!/usr/bin/env bash
+# conformance.sh - verify nit output matches git for equivalent commands
+#
+# Creates a test repo with known state, runs nit and git side by side,
+# and diffs the output. Any difference is a bug.
+#
+# Usage: ./tests/conformance.sh [path-to-nit-binary]
+
+set -euo pipefail
+
+NIT="${1:-./zig-out/bin/nit}"
+PASS=0
+FAIL=0
+ERRORS=""
+
+if [ ! -x "$NIT" ]; then
+  echo "error: nit binary not found at $NIT"
+  echo "       run: zig build -Doptimize=ReleaseFast"
+  exit 1
+fi
+
+# Resolve to absolute path
+NIT="$(cd "$(dirname "$NIT")" && pwd)/$(basename "$NIT")"
+
+TMPDIR=$(mktemp -d -t nit-conformance-XXXXXX)
+trap "rm -rf $TMPDIR" EXIT
+
+cd "$TMPDIR"
+git init -q
+git config user.email "test@test.com"
+git config user.name "Test User"
+
+# --- Build up a repo with various states ---
+
+# Initial commit
+cat > main.py << 'EOF'
+"""Main application."""
+
+import os
+import sys
+
+def main():
+    print("hello world")
+    return 0
+
+def helper(x):
+    """Helper function."""
+    if x > 0:
+        return x * 2
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(main())
+EOF
+
+cat > utils.py << 'EOF'
+"""Utility functions."""
+
+def add(a, b):
+    return a + b
+
+def subtract(a, b):
+    return a - b
+
+def multiply(a, b):
+    return a * b
+EOF
+
+git add main.py utils.py
+git commit -q -m "Initial commit"
+
+# Second commit - modify main.py
+sed -i.bak 's/hello world/hello nit/' main.py && rm -f main.py.bak
+git add main.py
+git commit -q -m "Update greeting message"
+
+# Third commit - add a file, modify utils
+cat > config.json << 'EOF'
+{
+  "name": "test",
+  "version": "1.0.0",
+  "debug": false
+}
+EOF
+
+cat >> utils.py << 'EOF'
+
+def divide(a, b):
+    if b == 0:
+        raise ValueError("division by zero")
+    return a / b
+EOF
+
+git add config.json utils.py
+git commit -q -m "Add config and divide function"
+
+# Fourth commit - delete a file
+git rm -q config.json
+git commit -q -m "Remove config file"
+
+# Now make some unstaged changes for status/diff testing
+sed -i.bak 's/hello nit/hello nit v2/' main.py && rm -f main.py.bak
+echo "# new file" > newfile.txt
+
+# Stage one change
+echo "extra_setting = true" >> utils.py
+git add utils.py
+
+# --- Test functions ---
+
+check() {
+  local name="$1"
+  local git_cmd="$2"
+  local nit_cmd="$3"
+
+  local git_out nit_out
+  git_out=$(eval "$git_cmd" 2>&1) || true
+  nit_out=$(eval "$nit_cmd" 2>&1) || true
+
+  if [ "$git_out" = "$nit_out" ]; then
+    PASS=$((PASS + 1))
+    echo "  PASS: $name"
+  else
+    FAIL=$((FAIL + 1))
+    echo "  FAIL: $name"
+    ERRORS="${ERRORS}\n--- FAIL: $name ---\n"
+    ERRORS="${ERRORS}git cmd: $git_cmd\n"
+    ERRORS="${ERRORS}nit cmd: $nit_cmd\n"
+    ERRORS="${ERRORS}git output:\n$git_out\n"
+    ERRORS="${ERRORS}nit output:\n$nit_out\n"
+  fi
+}
+
+echo "=== nit conformance tests ==="
+echo "repo: $TMPDIR"
+echo ""
+
+# --- Status tests ---
+echo "status:"
+# nit and git may sort differently (libgit2 vs git internals)
+# so compare sorted output
+check "porcelain entries match (sorted)" \
+  "git status --porcelain | sort" \
+  "$NIT status | sort"
+
+# --- Log tests ---
+echo ""
+echo "log:"
+check "oneline format matches" \
+  "git log --oneline -20" \
+  "$NIT log -n 20"
+
+check "oneline -5 matches" \
+  "git log --oneline -5" \
+  "$NIT log -n 5"
+
+check "oneline -1 matches" \
+  "git log --oneline -1" \
+  "$NIT log -n 1"
+
+# --- Diff tests (compare stripped nit vs git -U1, accounting for header differences) ---
+echo ""
+echo "diff:"
+
+# nit strips file headers to "--- path" and hunk context text.
+# Compare just the +/- content lines (exclude nit's "--- path" lines).
+check "unstaged change lines match" \
+  "git diff -U1 | grep '^[+-]' | grep -v '^[+-][+-][+-]'" \
+  "$NIT diff | grep '^[+-]' | grep -v '^--- '"
+
+check "staged change lines match" \
+  "git diff --staged -U1 | grep '^[+-]' | grep -v '^[+-][+-][+-]'" \
+  "$NIT diff -s | grep '^[+-]' | grep -v '^--- '"
+
+# --- Show tests ---
+echo ""
+echo "show:"
+
+# Compare the commit summary line
+check "show HEAD summary matches log" \
+  "git log --oneline -1" \
+  "$NIT show 2>&1 | head -1"
+
+# Show a specific revision
+SECOND_HASH=$(git log --oneline -3 | tail -1 | cut -d' ' -f1)
+check "show specific rev summary" \
+  "git log --oneline -1 $SECOND_HASH" \
+  "$NIT show $SECOND_HASH 2>&1 | head -1"
+
+# Show change lines match
+check "show HEAD change lines match" \
+  "git show -U1 HEAD | grep '^[+-]' | grep -v '^[+-][+-][+-]'" \
+  "$NIT show 2>&1 | grep '^[+-]' | grep -v '^--- '"
+
+# Show --stat
+check "show --stat file count matches" \
+  "git show --stat HEAD | tail -1 | grep -o '[0-9]* file' | head -1" \
+  "$NIT show --stat 2>&1 | sed -n '2p' | grep -o '[0-9]* file' | head -1"
+
+# --- Passthrough tests ---
+echo ""
+echo "passthrough:"
+
+check "branch passthrough" \
+  "git branch" \
+  "$NIT branch"
+
+check "log --graph passthrough" \
+  "git log --graph --oneline -3" \
+  "$NIT log --graph --oneline -3"
+
+check "diff --name-only passthrough" \
+  "git diff --name-only" \
+  "$NIT diff --name-only"
+
+check "diff --stat passthrough" \
+  "git diff --stat" \
+  "$NIT diff --stat"
+
+# --- Summary ---
+echo ""
+echo "=== results ==="
+echo "  passed: $PASS"
+echo "  failed: $FAIL"
+echo "  total:  $((PASS + FAIL))"
+
+if [ $FAIL -gt 0 ]; then
+  echo ""
+  echo "=== failures ==="
+  printf "$ERRORS"
+  exit 1
+fi