Add bunfig.toml flag to disable automatic .env file loading

Adds a new `dotenv` boolean field to bunfig.toml that controls whether
Bun automatically loads .env files at runtime. When set to false, .env
file loading is disabled while process.env still works normally.

This is useful for preventing accidental .env file loading in production
environments or when using alternative environment variable management.

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

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

docs/runtime/bunfig.md

@@ -109,6 +109,19 @@ The `telemetry` field permit to enable/disable the analytics records. Bun record
 telemetry = false
 ```
 
+### `dotenv`
+
+Control whether Bun automatically loads `.env` files. Default `true`.
+
+```toml
+# Disable automatic .env file loading
+dotenv = false
+```
+
+When set to `false`, Bun will not automatically load `.env`, `.env.local`, `.env.production`, `.env.development`, or `.env.test` files at runtime. Environment variables set in your shell or passed to the process will still be available via `process.env`.
+
+See [Runtime > Environment variables](/docs/runtime/env#disabling-automatic-env-file-loading) for more details.
+
 ### `console`
 
 Configure console output behavior.

docs/runtime/env.md

@@ -69,6 +69,20 @@ $ bun --env-file=.env.1 src/index.ts
 $ bun --env-file=.env.abc --env-file=.env.def run build
 ```
 
+### Disabling automatic `.env` file loading
+
+You can disable Bun's automatic `.env` file loading by setting `dotenv = false` in your [`bunfig.toml`](/docs/runtime/bunfig) configuration file.
+
+```toml#bunfig.toml
+dotenv = false
+```
+
+When disabled, Bun will not automatically load `.env`, `.env.local`, `.env.production`, `.env.development`, or `.env.test` files. However, environment variables set in your shell or passed to the process will still be available via `process.env`.
+
+{% callout %}
+**Note:** When `dotenv = false`, you can still manually load specific `.env` files using the `--env-file` flag.
+{% /callout %}
+
 ### Quotation marks
 
 Bun supports double quotes, single quotes, and template literal backticks:

src/api/schema.zig

@@ -1734,6 +1734,9 @@ pub const api = struct {
         /// from --unhandled-rejections, default is 'bun'
         unhandled_rejections: ?UnhandledRejections = null,
 
+        /// from bunfig.toml dotenv field, disables .env file loading when true
+        disable_dotenv: bool = false,
+
         bunfig_path: []const u8,
 
         pub fn decode(reader: anytype) anyerror!TransformOptions {

src/bunfig.zig

@@ -779,6 +779,18 @@ pub const Bunfig = struct {
                         }
                     }
                 }
+
+                if (json.get("dotenv")) |dotenv_expr| {
+                    if (dotenv_expr.asBool()) |value| {
+                        // When dotenv is set to false, disable .env loading
+                        // When true or not set, keep the default behavior
+                        if (!value) {
+                            this.bunfig.disable_dotenv = true;
+                        }
+                    } else {
+                        try this.addError(dotenv_expr.loc, "Expected boolean");
+                    }
+                }
             }
 
             if (json.getObject("serve")) |serve_obj2| {

src/transpiler.zig

@@ -474,6 +474,17 @@ pub const Transpiler = struct {
     }
 
     pub fn runEnvLoader(this: *Transpiler, skip_default_env: bool) !void {
+        // Check if dotenv is disabled via bunfig.toml
+        if (this.options.transform_options.disable_dotenv) {
+            // Skip .env loading but still load from process.env
+            try this.env.loadProcess();
+            if (this.env.isProduction()) {
+                this.options.setProduction(true);
+                this.resolver.opts.setProduction(true);
+            }
+            return;
+        }
+
         switch (this.options.env.behavior) {
             .prefix, .load_all, .load_all_without_inlining => {
                 // Step 1. Load the project root.

test/cli/run/env.test.ts

@@ -857,3 +857,45 @@ LARGE3="${"c".repeat(3000)}"
     expect(stdout).toBe("4096");
   });
 });
+
+describe("bunfig.toml dotenv flag", () => {
+  test("dotenv = false disables .env loading", () => {
+    const dir = tempDirWithFiles("bunfig-dotenv-disable", {
+      ".env": "FOO=from_env\n",
+      "bunfig.toml": "dotenv = false\n",
+      "index.ts": "console.log(process.env.FOO || 'undefined');",
+    });
+    const { stdout } = bunRun(`${dir}/index.ts`);
+    expect(stdout).toBe("undefined");
+  });
+
+  test("dotenv = false still allows process.env to work", () => {
+    const dir = tempDirWithFiles("bunfig-dotenv-disable-processenv", {
+      ".env": "FOO=from_env\n",
+      "bunfig.toml": "dotenv = false\n",
+      "index.ts": "console.log(process.env.BAR || 'undefined');",
+    });
+    const { stdout } = bunRun(`${dir}/index.ts`, { BAR: "from_process" });
+    expect(stdout).toBe("from_process");
+  });
+
+  test("dotenv = true allows .env loading (explicit)", () => {
+    const dir = tempDirWithFiles("bunfig-dotenv-enable", {
+      ".env": "FOO=from_env\n",
+      "bunfig.toml": "dotenv = true\n",
+      "index.ts": "console.log(process.env.FOO);",
+    });
+    const { stdout } = bunRun(`${dir}/index.ts`);
+    expect(stdout).toBe("from_env");
+  });
+
+  test("without bunfig.toml dotenv field, .env loads by default", () => {
+    const dir = tempDirWithFiles("bunfig-dotenv-default", {
+      ".env": "FOO=from_env\n",
+      "bunfig.toml": "# no dotenv field\n",
+      "index.ts": "console.log(process.env.FOO);",
+    });
+    const { stdout } = bunRun(`${dir}/index.ts`);
+    expect(stdout).toBe("from_env");
+  });
+});