Fix Bun.build({ env: "disable" }) not disabling NODE_ENV inlining

The JavaScript API was not properly handling env: "disable" - it needed to track when env was explicitly disabled and use .load_all_without_inlining behavior to prevent NODE_ENV from being inlined.

Fixes #19508

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/bun.js/api/JSBundler.zig

@@ -35,6 +35,7 @@ pub const JSBundler = struct {
         has_any_on_before_parse: bool = false,
         throw_on_error: bool = true,
         env_behavior: api.DotEnvBehavior = .disable,
+        env_explicitly_disabled: bool = false,
         env_prefix: OwnedString = OwnedString.initEmpty(bun.default_allocator),
         tsconfig_override: OwnedString = OwnedString.initEmpty(bun.default_allocator),
         compile: ?CompileOptions = null,
@@ -352,6 +353,7 @@ pub const JSBundler = struct {
                 if (!env.isUndefined()) {
                     if (env == .null or env == .false or (env.isNumber() and env.asNumber() == 0)) {
                         this.env_behavior = .disable;
+                        this.env_explicitly_disabled = true;
                     } else if (env == .true or (env.isNumber() and env.asNumber() == 1)) {
                         this.env_behavior = .load_all;
                     } else if (env.isString()) {
@@ -361,6 +363,7 @@ pub const JSBundler = struct {
                             this.env_behavior = .load_all;
                         } else if (strings.eqlComptime(slice.slice(), "disable")) {
                             this.env_behavior = .disable;
+                            this.env_explicitly_disabled = true;
                         } else if (strings.indexOfChar(slice.slice(), '*')) |asterisk| {
                             if (asterisk > 0) {
                                 this.env_behavior = .prefix;

src/bundler/bundle_v2.zig

@@ -1822,6 +1822,10 @@ pub const BundleV2 = struct {
             );
             transpiler.options.env.behavior = config.env_behavior;
             transpiler.options.env.prefix = config.env_prefix.slice();
+            // If env was explicitly disabled, prevent NODE_ENV inlining
+            if (config.env_explicitly_disabled) {
+                transpiler.options.env.behavior = .load_all_without_inlining;
+            }
             if (config.force_node_env != .unspecified) {
                 transpiler.options.force_node_env = config.force_node_env;
             }

test/regression/issue/19508.test.ts

@@ -0,0 +1,137 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
+import { join } from "path";
+
+test("Bun.build with env: 'disable' should not inline process.env.NODE_ENV (issue #19508)", async () => {
+  using dir = tempDir("build-env-disable", {
+    "input.js": `console.log(process.env.NODE_ENV);`,
+    "build.js": `
+      import { build } from "bun";
+      
+      const result = await build({
+        entrypoints: ["./input.js"],
+        outdir: "./dist",
+        env: "disable",
+      });
+      
+      if (!result.success) {
+        throw new Error("Build failed");
+      }
+    `,
+  });
+
+  // Run the build
+  const buildProc = Bun.spawn({
+    cmd: [bunExe(), "build.js"],
+    env: { ...bunEnv, NODE_ENV: "production" },
+    cwd: String(dir),
+    stderr: "pipe",
+    stdout: "pipe",
+  });
+
+  const [buildStdout, buildStderr, buildExitCode] = await Promise.all([
+    buildProc.stdout.text(),
+    buildProc.stderr.text(),
+    buildProc.exited,
+  ]);
+
+  expect(buildExitCode).toBe(0);
+
+  // Read the output file
+  const outputFile = Bun.file(join(String(dir), "dist", "input.js"));
+  const outputContent = await outputFile.text();
+
+  // The output should contain process.env.NODE_ENV, not the inlined value
+  expect(outputContent).toContain("process.env.NODE_ENV");
+  expect(outputContent).not.toContain('"production"');
+  expect(outputContent).not.toContain('"development"');
+
+  // Also test that it works correctly at runtime
+  const runProc = Bun.spawn({
+    cmd: [bunExe(), join("dist", "input.js")],
+    env: { ...bunEnv, NODE_ENV: "test-runtime" },
+    cwd: String(dir),
+    stdout: "pipe",
+  });
+
+  const [runStdout, runExitCode] = await Promise.all([runProc.stdout.text(), runProc.exited]);
+
+  expect(runExitCode).toBe(0);
+  expect(runStdout.trim()).toBe("test-runtime");
+});
+
+test("Bun.build CLI with --env=disable should not inline process.env.NODE_ENV", async () => {
+  using dir = tempDir("build-cli-env-disable", {
+    "input.js": `console.log(process.env.NODE_ENV);`,
+  });
+
+  // Run the build via CLI
+  const buildProc = Bun.spawn({
+    cmd: [bunExe(), "build", "./input.js", "--outdir", "./dist", "--env=disable"],
+    env: { ...bunEnv, NODE_ENV: "production" },
+    cwd: String(dir),
+    stderr: "pipe",
+    stdout: "pipe",
+  });
+
+  const [buildStdout, buildStderr, buildExitCode] = await Promise.all([
+    buildProc.stdout.text(),
+    buildProc.stderr.text(),
+    buildProc.exited,
+  ]);
+
+  expect(buildExitCode).toBe(0);
+
+  // Read the output file
+  const outputFile = Bun.file(join(String(dir), "dist", "input.js"));
+  const outputContent = await outputFile.text();
+
+  // The output should contain process.env.NODE_ENV, not the inlined value
+  expect(outputContent).toContain("process.env.NODE_ENV");
+  expect(outputContent).not.toContain('"production"');
+  expect(outputContent).not.toContain('"development"');
+});
+
+test("Bun.build with env: 'inline' should inline process.env.NODE_ENV", async () => {
+  using dir = tempDir("build-env-inline", {
+    "input.js": `console.log(process.env.NODE_ENV);`,
+    "build.js": `
+      import { build } from "bun";
+      
+      const result = await build({
+        entrypoints: ["./input.js"],
+        outdir: "./dist",
+        env: "inline",
+      });
+      
+      if (!result.success) {
+        throw new Error("Build failed");
+      }
+    `,
+  });
+
+  // Run the build with NODE_ENV=production
+  const buildProc = Bun.spawn({
+    cmd: [bunExe(), "build.js"],
+    env: { ...bunEnv, NODE_ENV: "production" },
+    cwd: String(dir),
+    stderr: "pipe",
+    stdout: "pipe",
+  });
+
+  const [buildStdout, buildStderr, buildExitCode] = await Promise.all([
+    buildProc.stdout.text(),
+    buildProc.stderr.text(),
+    buildProc.exited,
+  ]);
+
+  expect(buildExitCode).toBe(0);
+
+  // Read the output file
+  const outputFile = Bun.file(join(String(dir), "dist", "input.js"));
+  const outputContent = await outputFile.text();
+
+  // The output should contain the inlined value, not process.env.NODE_ENV
+  expect(outputContent).not.toContain("process.env.NODE_ENV");
+  expect(outputContent).toContain('"production"');
+});