dotenv 17.4.2: Pin dotenv multi-file path precedence reversal under override flags, unquoted comment truncation, and backtick quote escape semantics

# CodeSampleX Notes: dotenv Multi-Path Precedence & Parsing Semantics

## 1. Search Result
- **`search_known_solution`**: NO MATCH for npm `dotenv` (the search returned low-confidence references to unrelated Python packages: `packaging` SpecifierSet `sha256:2158f71f8f0182e574ebf8c6a651b8c00cc0e084fe82523db391f8d026016a3c`, distribution name mapping `sha256:beb8b3121c3cddc83a0038650f092bd1609123c82e31e1209dc60f07e688d56f`, and `pydantic-settings` `sha256:f5541d3ce0eda3656543ec05a42e65a6c79c2fcfe44febb312569405335bdce1`).

## 2. What a Model Would Have Written Instead
- A model would assume that passing `path: ['.env.local', '.env']` with `override: true` ensures `.env.local` overrides `.env` (matching standard frontend cascade order) while overriding host environment variables, that unquoted `#` in values (like URLs, passwords, or hex codes) is preserved as part of the value, and that backticks expand `\n` escape sequences like JavaScript template literals.

## 3. How the Wrong Version Fails
- It fails silently with a green build: under `override: true`, the array processing loop causes `.env` (the last file) to silently overwrite `.env.local` (the first file), unquoted `#` truncates database URLs/tokens without throwing an error, and backtick values retain unexpanded literal `\n` characters instead of LF newlines.

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  "name": "npm-dotenv-version",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "npm-dotenv-version",
      "version": "1.0.0",
      "license": "ISC",
      "dependencies": {
        "dotenv": "^17.4.2"
      }
    },
    "node_modules/dotenv": {
      "version": "17.4.2",
      "resolved": "https://registry.npmjs.org/dotenv/-/dotenv-17.4.2.tgz",
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{
  "name": "npm-dotenv-version",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "dependencies": {
    "dotenv": "17.4.2"
  }
}

import dotenv from 'dotenv';

/**
 * Loads configuration from multiple env file paths into a target environment object.
 *
 * @param {Object} params
 * @param {string[]} params.paths - Array of file paths to parse in order.
 * @param {Object} [params.targetEnv] - Destination object (defaults to an isolated object).
 * @param {boolean} [params.override=false] - Whether to override existing keys during population.
 * @param {boolean} [params.quiet=true] - Whether to suppress runtime injection logs.
 * @returns {{ parsed: Record<string, string>, target: Record<string, string>, error?: Error }}
 */
export function loadCascadeConfig({ paths, targetEnv = {}, override = false, quiet = true }) {
  const result = dotenv.configDotenv({
    path: paths,
    processEnv: targetEnv,
    override,
    quiet
  });

  return {
    parsed: result.parsed || {},
    target: targetEnv,
    error: result.error
  };
}

/**
 * Parses raw .env file string contents.
 *
 * @param {string} src - Raw env file content.
 * @returns {Record<string, string>}
 */
export function parseRawEnv(src) {
  return dotenv.parse(src);
}

/**
 * Populates a target object with parsed key-value pairs according to override settings.
 *
 * @param {Record<string, string>} target - Destination object to mutate.
 * @param {Record<string, string>} parsed - Key-value pairs to apply.
 * @param {Object} [options]
 * @param {boolean} [options.override=false] - Whether to overwrite existing keys on target.
 * @param {boolean} [options.debug=false]
 * @returns {Record<string, string>} Object containing ONLY keys that were newly written/populated.
 */
export function populateEnv(target, parsed, options = {}) {
  return dotenv.populate(target, parsed, options);
}

import assert from 'node:assert/strict';
import fs from 'node:fs';
import path from 'node:path';
import os from 'node:os';
import { loadCascadeConfig, parseRawEnv, populateEnv } from '../src/loader.mjs';

function runContract() {
  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'dotenv-csx-'));

  try {
    const baseEnvPath = path.join(tmpDir, '.env');
    const localEnvPath = path.join(tmpDir, '.env.local');

    fs.writeFileSync(
      baseEnvPath,
      [
        'API_PORT=3000',
        'CACHE_ENABLED=false',
        'LOG_LEVEL=info',
        'SERVICE_URL=https://example.com/api',
      ].join('\n')
    );

    fs.writeFileSync(
      localEnvPath,
      [
        'API_PORT=8080',
        'LOG_LEVEL=debug',
      ].join('\n')
    );

    // =========================================================================
    // 1. Multi-path cascade ordering: override=false vs override=true
    // =========================================================================

    // Case 1A: With override: false (default), the FIRST file in array sets keys;
    // subsequent files cannot overwrite earlier files in parsedAll.
    const initialTargetA = { PRESET_SYSTEM_VAR: 'from_host' };
    const resA = loadCascadeConfig({
      paths: [localEnvPath, baseEnvPath],
      targetEnv: initialTargetA,
      override: false,
    });

    assert.equal(resA.target.API_PORT, '8080', 'First file (.env.local) must win when override: false');
    assert.equal(resA.target.LOG_LEVEL, 'debug', '.env.local LOG_LEVEL must win over .env base');
    assert.equal(resA.target.CACHE_ENABLED, 'false', 'Unset keys in .env.local must fall back to .env');

    // Case 1B: If a key is already preset in targetEnv, override: false protects host env.
    const targetWithPreset = { API_PORT: '9999' };
    loadCascadeConfig({
      paths: [localEnvPath, baseEnvPath],
      targetEnv: targetWithPreset,
      override: false,
    });
    assert.equal(targetWithPreset.API_PORT, '9999', 'Existing host env must NOT be overwritten when override: false');

    // Case 1C: TRAP: When a naive caller sets override: true with [localEnv, baseEnv]
    // expecting .env.local to override .env while overriding host env, dotenv's internal loop
    // applies override: true sequentially, causing baseEnv (LAST file) to SILENTLY overwrite localEnv!
    const naiveTarget = { API_PORT: '9999' };
    loadCascadeConfig({
      paths: [localEnvPath, baseEnvPath],
      targetEnv: naiveTarget,
      override: true,
    });
    // In dotenv, with override: true and [local, base], the LAST file wins:
    assert.equal(naiveTarget.API_PORT, '3000', 'With override: true, the LAST file (.env base) silently overwrites .env.local');

    // Case 1D: The correct way to make .env.local override .env with override: true is REVERSED array order: [baseEnv, localEnv]
    const correctTarget = { API_PORT: '9999' };
    loadCascadeConfig({
      paths: [baseEnvPath, localEnvPath],
      targetEnv: correctTarget,
      override: true,
    });
    assert.equal(correctTarget.API_PORT, '8080', 'With override: true and [base, local], .env.local correctly wins and overrides host env');

    // =========================================================================
    // 2. Unquoted # inline comment truncation vs quoted values
    // =========================================================================
    const commentSample = [
      'UNQUOTED_HASH=secret#token_123',
      'UNQUOTED_URL=https://example.com/db#connection',
      'UNQUOTED_HEX=#10b981',
      'DOUBLE_QUOTED_HASH="secret#token_123"',
      'SINGLE_QUOTED_HASH=\'secret#token_123\'',
      'BACKTICK_HASH=`secret#token_123`',
    ].join('\n');

    const parsedComments = parseRawEnv(commentSample);
    // Unquoted # values are silently truncated as comments
    assert.equal(parsedComments.UNQUOTED_HASH, 'secret', 'Unquoted # must be silently truncated as comment');
    assert.equal(parsedComments.UNQUOTED_URL, 'https://example.com/db', 'Unquoted URL fragment # must be stripped');
    assert.equal(parsedComments.UNQUOTED_HEX, '', 'Unquoted hex starting with # becomes empty string');

    // Quoted values retain # intact
    assert.equal(parsedComments.DOUBLE_QUOTED_HASH, 'secret#token_123', 'Double quoted value must retain #');
    assert.equal(parsedComments.SINGLE_QUOTED_HASH, 'secret#token_123', 'Single quoted value must retain #');
    assert.equal(parsedComments.BACKTICK_HASH, 'secret#token_123', 'Backtick quoted value must retain #');

    // =========================================================================
    // 3. Escape sequences: Double quotes expand \n, Backticks and Single quotes do NOT
    // =========================================================================
    const escapeSample = [
      'DQUOTE_NEWLINE="line1\\nline2"',
      'SQUOTE_NEWLINE=\'line1\\nline2\'',
      'BACKTICK_NEWLINE=`line1\\nline2`',
    ].join('\n');

    const parsedEscapes = parseRawEnv(escapeSample);
    assert.equal(parsedEscapes.DQUOTE_NEWLINE, 'line1\nline2', 'Double quotes MUST expand \\n to literal LF (0x0A)');
    assert.equal(parsedEscapes.SQUOTE_NEWLINE, 'line1\\nline2', 'Single quotes MUST preserve literal \\n');
    assert.equal(parsedEscapes.BACKTICK_NEWLINE, 'line1\\nline2', 'Backticks MUST strip backticks but preserve literal \\n (no expansion)');

    // =========================================================================
    // 4. Colon delimiter and export prefix support
    // =========================================================================
    const syntaxSample = [
      'YAML_PORT: 8080',
      'export EXPORTED_HOST=localhost',
      'export EXPORTED_COLON: 127.0.0.1',
    ].join('\n');

    const parsedSyntax = parseRawEnv(syntaxSample);
    assert.equal(parsedSyntax.YAML_PORT, '8080', 'Colon : delimiter must be parsed as key-value separator');
    assert.equal(parsedSyntax.EXPORTED_HOST, 'localhost', 'Leading export prefix must be stripped');
    assert.equal(parsedSyntax.EXPORTED_COLON, '127.0.0.1', 'Leading export prefix with colon delimiter must work');

    // =========================================================================
    // 5. populate() return value vs target mutation semantics
    // =========================================================================
    const mutationTarget = { EXISTING_KEY: 'original' };
    const populatedReturn = populateEnv(
      mutationTarget,
      { EXISTING_KEY: 'will_be_ignored', FRESH_KEY: 'applied' },
      { override: false }
    );

    assert.equal(mutationTarget.EXISTING_KEY, 'original', 'target.EXISTING_KEY must remain unchanged');
    assert.equal(mutationTarget.FRESH_KEY, 'applied', 'target.FRESH_KEY must be populated');
    // populate() returns an object containing ONLY the keys that were newly written:
    assert.deepEqual(populatedReturn, { FRESH_KEY: 'applied' }, 'populate() must return only freshly written keys, omitting skipped existing keys');

    console.log('Contract passed: all dotenv version, precedence, escape, and mutation assertions verified.');
  } finally {
    fs.rmSync(tmpDir, { recursive: true, force: true });
  }
}

runContract();