coder/scripts/check_emdash.sh

#!/usr/bin/env bash
set -euo pipefail
# shellcheck source=scripts/lib.sh
source "$(dirname "${BASH_SOURCE[0]}")/lib.sh"
cdroot

echo "--- check for emdash/endash characters"

mode="changed"
for arg in "$@"; do
	if [[ "$arg" == "--all" ]]; then
		mode="all"
	fi
done

# Build the pattern from raw bytes so the script itself does not
# contain literal emdash/endash characters (which would trigger
# the check when the script is in the diff).
emdash=$'\xE2\x80\x94'
endash=$'\xE2\x80\x93'
pattern="${emdash}|${endash}"

# Git exclude_pathspecs excluded from the check. Used in both ls-files and diff comparison.
exclude_pathspecs=(
	":(exclude)aibridge/fixtures/**/*.txtar"
	# Generated CLI golden files embed serpent's emdash-bordered footer.
	":(exclude)cli/testdata/*.golden"
	":(exclude)enterprise/cli/testdata/*.golden"
)

scan_all_files() {
	local output
	output=$(git ls-files -z -- "${exclude_pathspecs[@]}" | xargs -0 grep -IEn "$pattern" 2>/dev/null || true)
	if [[ -n "$output" ]]; then
		echo "$output"
		found=1
	else
		found=0
	fi
}

# resolve_merge_base finds the merge-base between HEAD and the given ref.
# In shallow CI clones the merge-base is not directly reachable, so we
# query the PR commit count via `gh`, deepen HEAD by count+1, and
# resolve HEAD~N which is the parent of the first PR commit.
resolve_merge_base() {
	local base_ref="$1"

	# Fast path: merge-base already reachable (full clone or sufficient depth).
	local mb
	mb=$(git merge-base HEAD "$base_ref" 2>/dev/null || true)
	if [[ -n "$mb" ]]; then
		echo "$mb"
		return
	fi

	if ! command -v gh >/dev/null 2>&1; then
		echo "gh CLI not found, cannot determine PR commit count." >&2
		return
	fi

	# Use the PR commit count to deepen HEAD past the PR commits.
	# HEAD~N is the parent of the oldest PR commit, i.e. the merge-base.
	local count
	count=$(gh pr view --json commits --jq '.commits | length' 2>/dev/null || true)
	if [[ -z "$count" || "$count" -le 0 ]]; then
		echo "Could not determine PR commit count from gh." >&2
		return
	fi

	echo "Deepening HEAD by $((count + 1)) to reach PR base..." >&2
	git fetch --deepen="$((count + 1))" 2>/dev/null || true

	# Retry merge-base now that we have more history.
	mb=$(git merge-base HEAD "$base_ref" 2>/dev/null || true)
	if [[ -n "$mb" ]]; then
		echo "$mb"
		return
	fi

	# Last resort: walk first-parent history. This is correct for
	# linear PRs but may traverse the wrong branch for merge-commit
	# checkouts.
	git rev-parse --verify "HEAD~${count}" 2>/dev/null || true
}

# fetch_base_ref ensures origin/$GITHUB_BASE_REF is available locally.
# CI shallow clones (fetch-depth: 1) typically omit the base branch.
fetch_base_ref() {
	local base_ref="$1"

	if git rev-parse --verify "$base_ref" >/dev/null 2>&1; then
		return 0
	fi

	local ref="${base_ref#origin/}"
	echo "Base ref $base_ref not found locally, fetching $ref..." >&2
	git fetch origin "$ref" --depth=1 2>/dev/null || true

	if ! git rev-parse --verify "$base_ref" >/dev/null 2>&1; then
		echo "ERROR: could not fetch base ref $base_ref." >&2
		return 1
	fi
}

# resolve_diff_base determines the base ref to diff against.
resolve_diff_base() {
	# CI pull requests: use merge-base against the target branch.
	if [[ -n "${GITHUB_BASE_REF:-}" ]]; then
		local base_ref="origin/${GITHUB_BASE_REF}"
		fetch_base_ref "$base_ref" || return 1

		local base
		base=$(resolve_merge_base "$base_ref")
		if [[ -n "$base" ]]; then
			echo "$base"
			return
		fi

		# Could not determine merge-base; fall back to branch tip.
		echo "WARNING: could not find merge-base with $base_ref, using branch tip (diff may include non-PR changes)." >&2
		echo "$base_ref"
		return
	fi

	# Local dev: use merge-base with origin/main.
	if git rev-parse --verify origin/main >/dev/null 2>&1; then
		git merge-base HEAD origin/main 2>/dev/null || echo "origin/main"
		return
	fi
}

# scan_diff checks only added lines in the diff for emdash/endash.
scan_diff() {
	local base="$1"

	local diff_output
	if ! diff_output=$(git diff "$base" -U0 -- . "${exclude_pathspecs[@]}" 2>&1); then
		echo "ERROR: git diff against $base failed:" >&2
		echo "$diff_output" >&2
		exit 1
	fi

	if [[ -z "$diff_output" ]]; then
		echo "OK: no changes to check."
		exit 0
	fi

	local current_file="" current_line=0
	while IFS= read -r diff_line; do
		if [[ "$diff_line" =~ ^\+\+\+\ b/(.*) ]]; then
			current_file="${BASH_REMATCH[1]}"
		fi
		# Anchored to hunk header structure to avoid matching
		# digits from trailing function context.
		if [[ "$diff_line" =~ ^@@\ -[0-9,]+\ \+([0-9]+) ]]; then
			current_line=${BASH_REMATCH[1]}
			continue
		fi
		if [[ "$diff_line" =~ ^\+ ]] && [[ ! "$diff_line" =~ ^\+\+\+\ [ab/] ]]; then
			if echo "$diff_line" | grep -Eq "$pattern"; then
				echo "${current_file}:${current_line}:${diff_line:1}"
				found=1
			fi
			((current_line++)) || true
		fi
	done <<<"$diff_output"
}

if [[ "$mode" == "all" ]]; then
	scan_all_files
else
	base=$(resolve_diff_base) || {
		echo "ERROR: could not determine base ref." >&2
		exit 1
	}
	if [[ -z "$base" ]]; then
		echo "WARNING: no base ref found, scanning all tracked files." >&2
		scan_all_files
	else
		found=0
		scan_diff "$base"
	fi
fi

if [[ "$found" -ne 0 ]]; then
	echo ""
	echo "ERROR: Found emdash (U+2014) or endash (U+2013) characters."
	echo ""
	echo "  Do not use emdash or endash in code, comments, string literals,"
	echo "  or documentation. Use commas, semicolons, or periods instead."
	echo "  Restructure the sentence if needed. Do not replace them with"
	echo "  ' -- ' either."
	echo ""
	echo "  Example:"
	echo "    Bad:  This is slow [emdash] we should cache it."
	echo "    Good: This is slow. We should cache it."
	echo "    Good: This is slow, so we should cache it."
	echo ""
	exit 1
fi

echo "OK: no emdash or endash characters found."