Validate staged Go blobs in pre-commit gofmt check and include renames

[JordanCoin]

Motivation

• Prevent committing unformatted Go code by running gofmt against the staged blob rather than the working-tree file.
• Ensure renamed Go files are included in the check by adding R to the diff filter.

Description

• Update staged file selection to use git diff --cached --name-only --diff-filter=ACMR -- '*.go'.
• For each staged path read the staged blob with git show :<file> into a temp file, run gofmt -w on a copied temp file, and use cmp -s to detect formatting differences and collect unformatted staged paths.
• Improve failure output to list unformatted staged files and advise running gofmt -w <files> && git add <files>.

Testing

• Ran sh -n .githooks/pre-commit to validate shell syntax and it succeeded.

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Codex Task

[Copilot]

Pull request overview

Updates the repo’s Git pre-commit hook to validate gofmt against staged Go file content (rather than the working tree) and to include renamed Go files in the formatting check.

Changes:

• Expands staged file selection to include renames via --diff-filter=ACMR and limits to *.go.
• Reads each staged blob into a temp file, formats a copy, and compares to detect staged formatting drift.
• Improves failure output with staged-file wording and guidance to reformat + re-stage.

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[Copilot]

UNFORMATTED is built using \n escape sequences and printed with printf "%b" (lines 30, 40). If a filename contains backslashes, printf %b will interpret them as escapes and the output can be corrupted/misleading. Prefer accumulating real newlines (or a temp file) and printing with printf '%s\n' ... without %b escape processing.

[Copilot]

The here-doc body contains a leading space before $STAGED_GO (line 35). That causes the first staged path read by the loop to be prefixed with a space, so git show ":$file" won’t find the blob and the hook will silently skip the file (allowing unformatted code through). Remove the leading whitespace or feed the list to the loop in a way that doesn’t introduce indentation.

[Copilot]

mktemp is invoked without a template (lines 15–16). This fails on macOS/BSD mktemp (template is required), which would make the hook ineffective (and potentially allow unformatted code to be committed). Use a portable mktemp form (e.g., pass an explicit template path under ${TMPDIR:-/tmp}) and handle failures explicitly.

Suggested change

	orig=$(mktemp)
	formatted=$(mktemp)
	orig=$(mktemp "${TMPDIR:-/tmp}/gofmt.orig.XXXXXX") || {
	echo "pre-commit: failed to create temporary file for original content" >&2
	exit 1
	}
	formatted=$(mktemp "${TMPDIR:-/tmp}/gofmt.formatted.XXXXXX") || {
	echo "pre-commit: failed to create temporary file for formatted content" >&2
	rm -f "$orig"
	exit 1
	}