fix(bundler): inline Bun.env the same as process.env with --env

[SferaDev]

Fixes #20430

bun build --env=inline and bun build --env='PREFIX_*' inline process.env.<KEY> but leave Bun.env.<KEY> untouched. Since Bun.env is equivalent to process.env, both should be inlined.

The bundler's define system only registered process.env.<KEY> entries. This PR adds Bun.env.<KEY> defines alongside them in:

• env_loader.zig — copyForDefine, both prefix and load_all paths. Uses inline for over both prefixes to avoid duplication. Also tightened the e_strings allocation to the exact worst-case bound.
• options.zig — default NODE_ENV / BUN_ENV defines.
• HTMLBundle.zig — production NODE_ENV define in the Bake path.

Example

test.js

console.log(Bun.env.FOO)

Before:

$ FOO=hello bun build --env=inline test.js
console.log(Bun.env.FOO);

After:

$ FOO=hello bun build --env=inline test.js
console.log("hello");

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[coderabbitai]

Walkthrough

The PR extends environment variable inlining support to Bun.env alongside process.env during the build process. Changes enable Bun.env variants for both hardcoded (NODE_ENV, BUN_ENV) and custom environment variables to be inlined using dotenv inline mode and pattern matching, matching existing process.env behavior.

Changes

Cohort / File(s)	Summary
Build defines configuration src/bun.js/api/server/HTMLBundle.zig, src/options.zig	Extended production and development define setup to include both process.env and Bun.env variants for NODE_ENV and BUN_ENV definitions.
Environment loader src/env_loader.zig	Modified Loader.copyForDefine to generate environment-backed string literals for both process.env.<KEY> and Bun.env.<KEY> prefixes, with corresponding allocation sizing updates for buffer and scratch space.
Bundler tests test/bundler/bundler_env.test.ts	Added test cases validating Bun.env substitution behavior with dotenv inline mode and environment pattern matching (PUBLIC_*).

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: ensuring Bun.env is inlined alongside process.env when using the --env flag in the bundler.
Linked Issues check	✅ Passed	The PR fully addresses issue #20430 by adding Bun.env inlining support alongside process.env across env_loader.zig, options.zig, and HTMLBundle.zig, with comprehensive test coverage.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing Bun.env inlining behavior in the bundler across configuration, environment loading, and test files.
Description check	✅ Passed	PR description clearly explains the issue, changes made across three files, and provides concrete before/after examples.

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