[compiler] Add snap subcommand to minimize a test input

[everettbu]

Mirror of facebook/react#35663
Original author: josephsavona

---

Snap now supports subcommands 'test' (default) and 'minimize`. The minimize subcommand attempts to minimize a single failing input fixture by incrementally simplifying the ast so long as the same error occurs. I spot-checked it and it seemed to work pretty well. This is intended for use in a new subagent designed for investigating bugs — fixture simplification is an important part of the process and we can automate this rather than light tokens on fire.

Example Input:

function Component(props) {
  const x = [];
  let result;
  for (let i = 0; i < 10; i++) {
    if (cond) {
      try {
        result = {key: bar([props.cond && props.foo])};
      } catch (e) {
        console.log(e);
      }
    }
  }
  x.push(result);
  return <Stringify x={x} />;
}

Command output:

$ yarn snap minimize --path .../input.js
Minimizing: .../input.js

Minimizing................

--- Minimized Code ---
function Component(props) {
  try {
    props && props;
  } catch (e) {}
}

Reduced from 16 lines to 5 lines

This demonstrates things like:

• Removing one statement at at time
• Replacing if/else with the test, consequent, or alternate. Similar for other control-flow statements including try/catch
• Removing individual array/object expression properties
• Replacing single-value array/object with the value
• Replacing control-flow expression (logical, consequent) w the test or left/right values
• Removing call arguments
• Replacing calls with a single argument with the argument
• Replacing calls with multiple arguments with an array of the arguments
• Replacing optional member/call with non-optional versions
• Replacing member expression with the object. If computed, also try replacing w the key
• And a bunch more strategies, see the code

[greptile-apps]

Greptile Overview

Greptile Summary

This PR adds a new minimize subcommand to the snap testing tool that automatically reduces failing test inputs while preserving compiler errors. The implementation uses systematic AST simplification strategies (removing statements, simplifying expressions, etc.) to iteratively minimize code.

Key changes:

• Added comprehensive minimize.ts with 2070 lines implementing 30+ AST simplification strategies
• Refactored runner.ts from direct CLI parsing to yargs subcommand architecture (test as default, minimize as new command)
• Added @babel/generator dependency for code generation from AST

Issues found:

• Dependency version conflict in package.json: requests @babel/generator@^7.19.1 but forces resolution to 7.2.0
• Edge case bug in string parsing when input files lack newlines (two occurrences)

Confidence Score: 3/5

• Safe to merge after fixing the dependency conflict and newline edge case bugs
• The implementation is well-structured and comprehensive, but has two critical bugs that will cause runtime errors: the @babel/generator version conflict may cause unpredictable behavior, and the indexOf('\n') returning -1 will cause incorrect string slicing for single-line files
• Pay close attention to compiler/packages/snap/package.json and compiler/packages/snap/src/minimize.ts lines 49 and 2039

Important Files Changed

Filename	Overview
compiler/packages/snap/src/minimize.ts	Added new minimization feature with comprehensive AST simplification strategies to reduce failing test cases while preserving compiler errors
compiler/packages/snap/src/runner.ts	Refactored to support subcommands (test and minimize), moving from direct argument parsing to command-based structure
compiler/packages/snap/package.json	Added @babel/generator dependency with conflicting version resolution that may cause issues

[greptile-apps]

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[greptile-apps]

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[greptile-apps]

conflicting @babel/generator versions - dependency requests ^7.19.1 but resolution forces 7.2.0

Suggested change

	"@babel/code-frame": "^7.22.5",
	"@babel/generator": "^7.19.1",
	"@babel/code-frame": "^7.22.5",
	"@babel/generator": "^7.2.0",

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/snap/package.json
Line: 24:25

Comment:
conflicting `@babel/generator` versions - dependency requests `^7.19.1` but resolution forces `7.2.0`

```suggestion
    "@babel/code-frame": "^7.22.5",
    "@babel/generator": "^7.2.0",
```

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

potential issue if file contains no newline - indexOf('\n') returns -1, causing substring(0, -1) to return empty string

Suggested change

	const firstLine = input.substring(0, input.indexOf('\n'));
	const firstLine = input.includes('\n') ? input.substring(0, input.indexOf('\n')) : input;

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/snap/src/minimize.ts
Line: 2039:2039

Comment:
potential issue if file contains no newline - `indexOf('\n')` returns -1, causing `substring(0, -1)` to return empty string

```suggestion
  const firstLine = input.includes('\n') ? input.substring(0, input.indexOf('\n')) : input;
```

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

same issue - if code has no newline, indexOf('\n') returns -1

Suggested change

	const firstLine = code.substring(0, code.indexOf('\n'));
	const firstLine = code.includes('\n') ? code.substring(0, code.indexOf('\n')) : code;

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/snap/src/minimize.ts
Line: 49:49

Comment:
same issue - if `code` has no newline, `indexOf('\n')` returns -1

```suggestion
  const firstLine = code.includes('\n') ? code.substring(0, code.indexOf('\n')) : code;
```

How can I resolve this? If you propose a fix, please make it concise.

[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.