implement build api `define` and `loaders` (#2805)

* parse error logs

* clean up types

* remove --jsx-production. use NODE_ENV instead

* add define to js api

* add loaders to js api

* fixups

* sourcemap

* typo fix

* remove label, comment dir just for now

* test tweaks

* test work

* make optional enums actually optional.
allows `sourcemap: undefined`

* overload host ram test

* string tests

* tests

* test for 2815

* requested changes

* sort this list

* remove this test file now that it passes

* oops

* add --format

* finish ts tests

* doc typos related to define and loader

2 files changed, 87 insertions, 17 deletions

diff --git a/docs/bundler/migration.md b/docs/bundler/migration.md
index 260acf1ba..aac37479c 100644
--- a/docs/bundler/migration.md
+++ b/docs/bundler/migration.md
@@ -63,8 +63,8 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 ---
 
-- `--loader`
-- `--loader`
+- `--loader:.ext=loader`
+- `--loader .ext:loader`
 - Bun supports a different set of built-in loaders than esbuild; see [Bundler > Loaders](/docs/bundler/loaders) for a complete reference. The esbuild loaders `dataurl`, `binary`, `base64`, `copy`, and `empty` are not yet implemented.
 
   The syntax for `--loader` is slightly different.
@@ -131,7 +131,7 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--watch`
 - n/a
-- Not applicable.
+- Not applicable
 
 ---
 
@@ -143,7 +143,7 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--analyze`
 - n/a
-- Not supported. Use `--manifest` to generate a manifest file.
+- Not supported
 
 ---
 
@@ -161,7 +161,7 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--certfile`
 - n/a
-- Not applicable, Bun's bundler does
+- Not applicable
 
 ---
 
@@ -203,7 +203,7 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--global-name`
 - n/a
-- Not applicable, Bun does not support `iife` output at this time.
+- Not applicable, Bun does not support `iife` output at this time
 
 ---
 
@@ -248,7 +248,7 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--jsx-side-effects`
 - n/a
-- JSX is always assumed to be side-effect-free.
+- JSX is always assumed to be side-effect-free
 
 ---
 
@@ -313,7 +313,8 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 ---
 
 - `--metafile`
-- `--manifest`
+- n/a
+- Not supported
 
 ---
 
@@ -340,7 +341,6 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `--outbase`
 - `--root`
-- Not supported
 
 ---
 
@@ -515,7 +515,6 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 
 - `define`
 - `define`
-- Not supported in JS API
 
 ---
 
@@ -637,8 +636,8 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 ---
 
 - `loader`
-- n/a
-- Not supported in JS API
+- `loader`
+- Bun supports a different set of built-in loaders than esbuild; see [Bundler > Loaders](/docs/bundler/loaders) for a complete reference. The esbuild loaders `dataurl`, `binary`, `base64`, `copy`, and `empty` are not yet implemented.
 
 ---
 
@@ -685,8 +684,11 @@ In Bun's CLI, simple boolean flags like `--minify` do not accept an argument. Ot
 ---
 
 - `metafile`
-- `manifest`
-- When `manifest` is `true`, the result of `Bun.build()` will contain a `manifest` property. The manifest is compatible with esbuild's metafile format.
+- n/a
+- Not supported
+
+<!-- - `manifest`
+- When `manifest` is `true`, the result of `Bun.build()` will contain a `manifest` property. The manifest is compatible with esbuild's metafile format. -->
 
 ---
 
diff --git a/docs/cli/build.md b/docs/cli/build.md
index f205969d5..01262944d 100644
--- a/docs/cli/build.md
+++ b/docs/cli/build.md
@@ -324,7 +324,7 @@ Depending on the target, Bun will apply different module resolution rules and op
 
 {% /table %}
 
-<!-- ### `module`
+### `format`
 
 Specifies the module format to be used in the generated bundles.
 
@@ -714,6 +714,24 @@ var value = z.string().parse("Hello world!")
 console.log(_.upperCase(value));
 ```
 
+To mark all imports as external, use the wildcard `*`:
+
+{% codetabs %}
+
+```ts#JavaScript
+await Bun.build({
+  entrypoints: ['./index.tsx'],
+  outdir: './out',
+  external: ['*'],
+})
+```
+
+```bash#CLI
+$ bun build ./index.tsx --outdir ./out --external '*'
+```
+
+{% /codetabs %}
+
 ### `naming`
 
 Customizes the generated file names. Defaults to `./[dir]/[name].[ext]`.
@@ -988,6 +1006,56 @@ The output file would now look something like this.
 + var logo = 'https://cdn.example.com/logo-a7305bdef.svg';
 ```
 
+### `define`
+
+A map of global identifiers to be replaced at build time. Keys of this object are identifier names, and values are JSON strings that will be inlined.
+
+{% callout }
+This is not needed to inline `process.env.NODE_ENV`, as Bun does this automatically.
+{% /callout %}
+
+{% codetabs %}
+
+```ts#JavaScript
+await Bun.build({
+  entrypoints: ['./index.tsx'],
+  outdir: './out',
+  define: {
+    STRING: JSON.stringify("value"),
+    "nested.boolean": "true",
+  },
+})
+```
+
+```bash#CLI
+$ bun build ./index.tsx --outdir ./out --define 'STRING="value"' --define "nested.boolean=true"
+```
+
+{% /codetabs %}
+
+### `loader`
+
+A map of file extensions to [built-in loader names](https://bun.sh/docs/bundler/loaders#built-in-loaders). This can be used to quickly customize how certain file files are loaded.
+
+{% codetabs %}
+
+```ts#JavaScript
+await Bun.build({
+  entrypoints: ['./index.tsx'],
+  outdir: './out',
+  loader: {
+    ".png": "dataurl",
+    ".txt": "file",
+  },
+})
+```
+
+```bash#CLI
+$ bun build ./index.tsx --outdir ./out --loader .png:dataurl --loader .txt:file
+```
+
+{% /codetabs %}
+
 ## Reference
 
 ```ts
@@ -1003,8 +1071,8 @@ interface BuildOptions {
   outdir?: string; // default: no write (in-memory only)
   target?: "browser" | "bun" | "node"; // "browser"
   splitting?: boolean; // true
-  plugins?: BunPlugin[]; // []
-  loader?: { [k in string]: Loader };
+  plugins?: BunPlugin[]; // [] // See https://bun.sh/docs/bundler/plugins
+  loader?: { [k in string]: Loader }; // See https://bun.sh/docs/bundler/loaders
   manifest?: boolean; // false
   external?: string[]; // []
   sourcemap?: "none" | "inline" | "external"; // "none"