Before reading thousands of diff hunks from a free or local code-generation model, first map what changed: which paths were added, deleted, renamed or copied; how many lines each path gained or lost; and which directories absorbed the work. Git’s summary, name-status, numstat, shortstat and dirstat views provide that map. They describe the shape and volume of one comparison, not whether the generated code is correct, safe or tested.
What a diff autopsy can—and cannot—tell you
A generated patch can look plausible while quietly removing a configuration file, touching an unexpected subsystem or rewriting far more code than the task requires. A short structural pass makes those possibilities visible before you spend time on individual hunks.
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The method in this guide is a worksheet built from Git’s documented diff outputs. It is not a model-quality score, a defect detector or a substitute for tests. A deletion may be an intentional migration; a large line count may be a formatting pass; a concentrated directory share may be exactly what the task requested. Treat every signal as a prompt to ask a repository-specific question.
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- Line churn: record additions and deletions per path, then the aggregate totals.
- Repository shape: see which subdirectories contain the change and which dirstat mode produced that view.
- Context: compare those observations with the requested task, the compared revisions and the project’s normal validation.
Git documents these formats in its git-diff documentation. The commands below show a repeatable way to capture them.
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1. Define exactly what you are comparing
A summary is meaningful only when the comparison range is clear. Write down whether you are inspecting a commit range, a branch against its base, or uncommitted work in the index and working tree. The same command can report very different changes depending on that choice.
Committed range
git diff BASE..HEADReplace BASE and HEAD with the revisions you intend to compare. For a pull request, use the project’s stated base and feature revisions rather than assuming that the currently checked-out branch is the right endpoint.
Working tree and index
git diff # unstaged changes against the index
git diff --cached # staged changes against HEAD
git diff HEAD # staged and unstaged changes against HEADThese commands answer different questions. If a generated tool edited files but you have not staged them, git diff omits anything already in the index. Capture the state you actually plan to review and record it beside the worksheet.
Keep the scope stable
- Record the two revisions or the working-tree state.
- Note any pathspec you used, because restricting the command to a directory hides changes elsewhere.
- Do not mix a full-repository summary with a later hunk review of only a subdirectory without marking the change in scope.
Also record whether the comparison is made from a clean checkout or from a workspace containing unrelated edits. An uncommitted workspace can make a generated patch appear broader than the requested task. If you cannot isolate the change, state that limitation on the sheet and avoid treating the totals as belonging solely to the generator.
2. Flag path status before looking at line counts
Start with a path-oriented view. Git’s --summary option produces a condensed description of newly added, deleted, renamed and copied files. --name-status lists changed names with status letters, which is convenient when you want a compact, machine-readable worksheet.
Use the condensed summary
git diff --summary BASE..HEADReview every line for a deletion, rename or copy. These statuses tell you where the repository’s shape changed, even when the textual diff is small.
Use name-status when you need a path ledger
git diff --name-status BASE..HEADCopy the output into a table with columns for status and path. If your repository uses rename detection, a rename can include old and new names; preserve both names in your notes. The status is a review prompt, not a verdict: a deleted generated artifact may be expected, while deletion of an entry point may demand immediate explanation.
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Questions for every deletion
- Was the path explicitly removed by the task, or did the generator infer that it was obsolete?
- Is there a replacement path, and does the build or deployment configuration point to it?
- Was the file tracked, generated, or a hand-maintained fixture?
- Does the repository’s history or contribution guide explain deletion conventions?
Do not label a deletion a bug merely because it appears in the summary. Its meaning depends on the repository and the requested change.
Read status and path together
A status ledger is most useful when each row keeps the exact path spelling Git emitted. Do not collapse a rename into only its destination, and do not discard a copy’s source path. Keeping both sides lets you search references to the old location and check whether packaging, imports, documentation or deployment files still mention it. For a deleted path, add a short explanation column and leave it blank until a task statement, history entry or repository convention supports the explanation.
3. Measure per-file churn with numstat
Once statuses are recorded, measure line movement. Git’s --numstat output gives added and deleted line counts for each path in a diff. It is useful for sorting attention: a one-line change and a wholesale rewrite should not receive the same first-pass treatment.
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git diff --numstat BASE..HEADThe normal text form has three fields: additions, deletions and the path. Binary files are represented with - counts rather than line numbers, because line-based measurement does not apply. Preserve that distinction in the worksheet instead of converting it to zero.
Build a per-path worksheet
| Path | Status | Added lines | Deleted lines | Review note |
|---|---|---|---|---|
src/... |
from --name-status |
from --numstat |
from --numstat |
Why this amount of change? |
| Binary asset path | status output | - |
- |
Inspect the binary change and its consumer. |
The table is a recording format, not a threshold system. A large addition can be the intended implementation; a tiny deletion can remove a critical permission check. Use the counts to choose questions, then read the relevant hunks.
Distinguish churn from movement
Line counts describe the diff Git calculated. A formatter, import reorder or file split can create substantial additions and deletions without equivalent new behavior. Conversely, a moved block may be recognized as a rename or movement depending on diff settings. That is why counts must be read with status output and the actual hunks.
Do not add binary dashes as if they were numeric zeros when checking your worksheet. Mark those rows as non-line-countable and inspect the asset, its metadata and the code that consumes it. Likewise, do not compare a text file’s additions directly with a binary file’s status as though both measured the same kind of change.
4. Capture the aggregate with shortstat
--shortstat prints the final totals line of the stat output: the number of changed files and the aggregate insertions and deletions for the selected comparison.
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The aggregate is descriptive. Git does not define a universal “too many lines” value, and the documentation does not turn shortstat totals into a risk score. A project may establish its own review thresholds, but label them as local policy rather than a general rule.
Use shortstat as a completeness check, not as a substitute for the path ledger. It cannot tell you which file accounts for the total, whether a deletion was intentional, or whether the changed files belong to the requested component. Reconcile it after collecting numstat rows, then use the per-path values to decide where detailed reading starts.
5. Map where the change landed with dirstat
Line totals tell you how much changed; --dirstat tells you how the change is distributed across subdirectories. This helps detect a task that unexpectedly spread from one package into build scripts, documentation or deployment configuration.
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git diff --dirstat=changes,0 BASE..HEADThe first parameter selects the accounting mode and the second controls the percentage cutoff. A zero cutoff asks Git to show all directories that contribute to the distribution; choose another cutoff when a concise view is more useful, and record it in your worksheet.
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Choose the mode deliberately
| Mode | What it measures | When it helps |
|---|---|---|
changes |
Removed and added source lines, with pure code movement discounted. | Estimate substantive line changes while reducing the effect of moved blocks. |
lines |
The regular line-based diff analysis. | See distribution using the same line accounting as an ordinary textual diff. |
files |
Contribution based on changed-file counts. | Understand breadth when many small files matter more than line volume. |
These mode definitions come from Git’s documentation. They answer different distribution questions, so do not compare percentages from different modes as if they were the same metric.
Run all three when the shape is surprising
git diff --dirstat=changes,0 BASE..HEAD
git diff --dirstat=lines,0 BASE..HEAD
git diff --dirstat=files,0 BASE..HEADIf one directory dominates files but not lines, it contains many small edits. If it dominates lines but not files, a small number of files received large rewrites. A difference between changes and lines can indicate that movement is affecting the distribution. None of these patterns proves a defect; each tells you where to focus context checks.
Always write the mode and cutoff beside the percentages. A dirstat view with a nonzero cutoff can omit smaller contributors, while a zero cutoff exposes every directory Git includes in the calculation. Re-running the command with a different cutoff is a new observation, not a correction to the first one.
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Keep one record for the exact comparison. A practical sheet has four sections.
Comparison identity
- Base and endpoint revisions, or the working-tree/index state.
- Date and time of capture.
- Repository and pathspec scope.
- Dirstat mode and cutoff.
Path status
Paste the --summary or --name-status output. Mark every deleted path for an explicit explanation, and retain both sides of a rename.
Churn
Paste --numstat rows and the --shortstat total. For text files, note additions and deletions; for binary files, preserve Git’s - markers and inspect the consuming code or asset metadata instead of inventing line counts.
Directory distribution
Paste the selected --dirstat output and label the mode. If the distribution does not match the task’s stated scope, list the directories that need explanation before reviewing implementation details.
Make the sheet reviewable by someone else
Include the command text, not only copied results, so another reviewer can reproduce the comparison. Keep outputs from the same revision range together and note any pathspec or option that narrows scope. Add a free-text question beside each anomaly—such as “Why is deployment configuration touched?”—rather than marking it as a defect. This preserves the distinction between an observation and the conclusion reached after reading code and running validation.
7. Compare the shape with the requested task
The worksheet becomes useful when you ask whether the observed shape is plausible for the requested change.
Match paths to the task
List the files or components the task named, then compare them with the status ledger. Extra paths are not automatically wrong: a feature may require tests, fixtures, documentation or configuration. They are evidence that the generated change made assumptions you should verify.
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Explain deletions and renames
For each deletion or rename, identify the replacement behavior, update references and confirm that build, packaging and deployment files still agree. If no explanation exists in the task or project conventions, stop the hunk review long enough to resolve that ambiguity.
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Interpret large churn locally
Look at the paths with the highest additions plus deletions. Determine whether the volume comes from new functionality, a generated file, formatting, a dependency update or a broad rewrite. The number alone cannot establish correctness or defect risk.
Check directory concentration
Compare dirstat output with the architecture implied by the task. A request confined to one service that also changes repository-wide automation deserves a scope question. A cross-cutting change that touches only one leaf directory may indicate missing integration work. These are review hypotheses, not conclusions.
8. Move from shape to evidence
After the structural pass, inspect the hunks selected by your worksheet. Start with deleted paths and high-churn files, then follow references into the directories highlighted by dirstat. Read tests and configuration alongside implementation so that a plausible code change is not mistaken for a complete change.
Run the project’s ordinary validation after understanding the scope. The Git summaries do not prescribe a test regimen, and they cannot show whether tests pass, whether a security property holds or whether a free model generated the patch. Use the repository’s own documented commands and review requirements.
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“A deletion means the model introduced a bug.”
Recovery: inspect the task, history and references. Confirm whether the path was intentionally retired, replaced or generated. Keep the deletion flagged until that explanation is documented.
“More changed lines means lower quality.”
Recovery: classify the churn. Formatting, movement and generated artifacts can inflate counts; a small change can still alter critical behavior. Read the affected hunks and validation results.
“Dirstat proves the model worked in the wrong area.”
Recovery: verify the mode and cutoff first, then compare the directories with the task’s dependency graph. Different modes answer different distribution questions, and none is a correctness test.
“The totals from two commands should always match.”
Recovery: rerun them with identical revisions, pathspecs and relevant options. A working-tree diff, staged diff and commit-range diff are different comparisons. Rename and binary handling can also change how output is represented.
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“A threshold from another project is universal.”
Recovery: treat thresholds as project-specific policy. Git documents output formats, not a population-wide suspicious-churn cutoff. Record why your team chose a limit and revisit it as the repository changes.
“A copied path is harmless because the original still exists.”
Recovery: identify which copy is now referenced and whether both files are meant to remain authoritative. Check build and packaging lists, since duplicated configuration or source can create divergent maintenance paths even when no deletion appears.
10. What the available evidence does not establish
Git’s documentation establishes how these summaries are produced; it does not claim that they predict model quality, safety, correctness or test success. The preliminary paper Linking Code and Documentation Churn: Preliminary Analysis describes a proposed repository-mining study, but the available result does not justify turning its framing into a universal rule or a quantified review threshold. You can read it at arXiv:2410.05992.
Accordingly, label your sheet as an observation of one diff. Do not present its line counts as general research statistics, and do not infer how a free model behaves from the summaries alone.
Copyable command sequence
Run the following sequence after replacing the revision range. Save each output with the same comparison identity.
git diff --summary BASE..HEAD
git diff --name-status BASE..HEAD
git diff --numstat BASE..HEAD
git diff --shortstat BASE..HEAD
git diff --dirstat=changes,0 BASE..HEAD
git diff --dirstat=lines,0 BASE..HEAD
git diff --dirstat=files,0 BASE..HEADThen mark deleted paths, reconcile per-file counts with the shortstat total, annotate binary - values, and compare the directory distribution with the requested scope. Only after that should you spend time on every patch hunk.
Frequently Asked Questions
How do I check what an AI-generated code change deleted before reviewing it?
Run git diff --summary BASE..HEAD or git diff --name-status BASE..HEAD, then mark every deleted path. Check the task, repository history, references and any replacement path before deciding whether the deletion is intentional.
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How can I see which files changed and how many lines were added or removed?
Use git diff --numstat BASE..HEAD for additions and deletions by path, and git diff --shortstat BASE..HEAD for the aggregate changed-file, insertion and deletion totals. Keep the same revisions and pathspec for both commands.
How do I tell which parts of my repository a diff touched?
Use git diff --dirstat=changes,0 BASE..HEAD. If the result is surprising, compare it with lines and files modes, recording the mode and cutoff because each measures distribution differently.
What does a dash in numstat mean?
Git uses - for additions and deletions when a path is binary, because line counts do not apply. Preserve the dashes instead of converting them to zero, and inspect the binary asset and its consumers separately.
Is there a universal number of changed lines that should block review?
No. Git documents how to report counts but does not define a universal suspicious-churn threshold. If your team sets a limit, treat it as project-specific policy and explain its rationale.
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Should I review hunks before running these commands?
The worksheet is intended as a quick structural pass first. Capture the comparison identity, statuses, numstat, shortstat and dirstat, then use those observations to prioritize hunks and run the project’s normal validation.
The Bottom Line
Use Git’s summary, name-status, numstat, shortstat and dirstat outputs to map a generated change before reading every hunk. Flag deletions, preserve binary markers, reconcile totals and record directory scope—but treat every result as a question about this repository, never as a correctness or model-quality score.
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