219 lines
7.1 KiB
Markdown
Executable File
219 lines
7.1 KiB
Markdown
Executable File
# @ampproject/remapping
|
|
|
|
> Remap sequential sourcemaps through transformations to point at the original source code
|
|
|
|
Remapping allows you to take the sourcemaps generated through transforming your code and "remap"
|
|
them to the original source locations. Think "my minified code, transformed with babel and bundled
|
|
with webpack", all pointing to the correct location in your original source code.
|
|
|
|
With remapping, none of your source code transformations need to be aware of the input's sourcemap,
|
|
they only need to generate an output sourcemap. This greatly simplifies building custom
|
|
transformations (think a find-and-replace).
|
|
|
|
## Installation
|
|
|
|
```sh
|
|
npm install @ampproject/remapping
|
|
```
|
|
|
|
## Usage
|
|
|
|
```typescript
|
|
function remapping(
|
|
map: SourceMap | SourceMap[],
|
|
loader: (file: string, ctx: LoaderContext) => (SourceMap | null | undefined),
|
|
options?: { excludeContent: boolean, decodedMappings: boolean }
|
|
): SourceMap;
|
|
|
|
// LoaderContext gives the loader the importing sourcemap, tree depth, the ability to override the
|
|
// "source" location (where child sources are resolved relative to, or the location of original
|
|
// source), and the ability to override the "content" of an original source for inclusion in the
|
|
// output sourcemap.
|
|
type LoaderContext = {
|
|
readonly importer: string;
|
|
readonly depth: number;
|
|
source: string;
|
|
content: string | null | undefined;
|
|
}
|
|
```
|
|
|
|
`remapping` takes the final output sourcemap, and a `loader` function. For every source file pointer
|
|
in the sourcemap, the `loader` will be called with the resolved path. If the path itself represents
|
|
a transformed file (it has a sourcmap associated with it), then the `loader` should return that
|
|
sourcemap. If not, the path will be treated as an original, untransformed source code.
|
|
|
|
```js
|
|
// Babel transformed "helloworld.js" into "transformed.js"
|
|
const transformedMap = JSON.stringify({
|
|
file: 'transformed.js',
|
|
// 1st column of 2nd line of output file translates into the 1st source
|
|
// file, line 3, column 2
|
|
mappings: ';CAEE',
|
|
sources: ['helloworld.js'],
|
|
version: 3,
|
|
});
|
|
|
|
// Uglify minified "transformed.js" into "transformed.min.js"
|
|
const minifiedTransformedMap = JSON.stringify({
|
|
file: 'transformed.min.js',
|
|
// 0th column of 1st line of output file translates into the 1st source
|
|
// file, line 2, column 1.
|
|
mappings: 'AACC',
|
|
names: [],
|
|
sources: ['transformed.js'],
|
|
version: 3,
|
|
});
|
|
|
|
const remapped = remapping(
|
|
minifiedTransformedMap,
|
|
(file, ctx) => {
|
|
|
|
// The "transformed.js" file is an transformed file.
|
|
if (file === 'transformed.js') {
|
|
// The root importer is empty.
|
|
console.assert(ctx.importer === '');
|
|
// The depth in the sourcemap tree we're currently loading.
|
|
// The root `minifiedTransformedMap` is depth 0, and its source children are depth 1, etc.
|
|
console.assert(ctx.depth === 1);
|
|
|
|
return transformedMap;
|
|
}
|
|
|
|
// Loader will be called to load transformedMap's source file pointers as well.
|
|
console.assert(file === 'helloworld.js');
|
|
// `transformed.js`'s sourcemap points into `helloworld.js`.
|
|
console.assert(ctx.importer === 'transformed.js');
|
|
// This is a source child of `transformed`, which is a source child of `minifiedTransformedMap`.
|
|
console.assert(ctx.depth === 2);
|
|
return null;
|
|
}
|
|
);
|
|
|
|
console.log(remapped);
|
|
// {
|
|
// file: 'transpiled.min.js',
|
|
// mappings: 'AAEE',
|
|
// sources: ['helloworld.js'],
|
|
// version: 3,
|
|
// };
|
|
```
|
|
|
|
In this example, `loader` will be called twice:
|
|
|
|
1. `"transformed.js"`, the first source file pointer in the `minifiedTransformedMap`. We return the
|
|
associated sourcemap for it (its a transformed file, after all) so that sourcemap locations can
|
|
be traced through it into the source files it represents.
|
|
2. `"helloworld.js"`, our original, unmodified source code. This file does not have a sourcemap, so
|
|
we return `null`.
|
|
|
|
The `remapped` sourcemap now points from `transformed.min.js` into locations in `helloworld.js`. If
|
|
you were to read the `mappings`, it says "0th column of the first line output line points to the 1st
|
|
column of the 2nd line of the file `helloworld.js`".
|
|
|
|
### Multiple transformations of a file
|
|
|
|
As a convenience, if you have multiple single-source transformations of a file, you may pass an
|
|
array of sourcemap files in the order of most-recent transformation sourcemap first. Note that this
|
|
changes the `importer` and `depth` of each call to our loader. So our above example could have been
|
|
written as:
|
|
|
|
```js
|
|
const remapped = remapping(
|
|
[minifiedTransformedMap, transformedMap],
|
|
() => null
|
|
);
|
|
|
|
console.log(remapped);
|
|
// {
|
|
// file: 'transpiled.min.js',
|
|
// mappings: 'AAEE',
|
|
// sources: ['helloworld.js'],
|
|
// version: 3,
|
|
// };
|
|
```
|
|
|
|
### Advanced control of the loading graph
|
|
|
|
#### `source`
|
|
|
|
The `source` property can overridden to any value to change the location of the current load. Eg,
|
|
for an original source file, it allows us to change the location to the original source regardless
|
|
of what the sourcemap source entry says. And for transformed files, it allows us to change the
|
|
relative resolving location for child sources of the loaded sourcemap.
|
|
|
|
```js
|
|
const remapped = remapping(
|
|
minifiedTransformedMap,
|
|
(file, ctx) => {
|
|
|
|
if (file === 'transformed.js') {
|
|
// We pretend the transformed.js file actually exists in the 'src/' directory. When the nested
|
|
// source files are loaded, they will now be relative to `src/`.
|
|
ctx.source = 'src/transformed.js';
|
|
return transformedMap;
|
|
}
|
|
|
|
console.assert(file === 'src/helloworld.js');
|
|
// We could futher change the source of this original file, eg, to be inside a nested directory
|
|
// itself. This will be reflected in the remapped sourcemap.
|
|
ctx.source = 'src/nested/transformed.js';
|
|
return null;
|
|
}
|
|
);
|
|
|
|
console.log(remapped);
|
|
// {
|
|
// …,
|
|
// sources: ['src/nested/helloworld.js'],
|
|
// };
|
|
```
|
|
|
|
|
|
#### `content`
|
|
|
|
The `content` property can be overridden when we encounter an original source file. Eg, this allows
|
|
you to manually provide the source content of the original file regardless of whether the
|
|
`sourcesContent` field is present in the parent sourcemap. It can also be set to `null` to remove
|
|
the source content.
|
|
|
|
```js
|
|
const remapped = remapping(
|
|
minifiedTransformedMap,
|
|
(file, ctx) => {
|
|
|
|
if (file === 'transformed.js') {
|
|
// transformedMap does not include a `sourcesContent` field, so usually the remapped sourcemap
|
|
// would not include any `sourcesContent` values.
|
|
return transformedMap;
|
|
}
|
|
|
|
console.assert(file === 'helloworld.js');
|
|
// We can read the file to provide the source content.
|
|
ctx.content = fs.readFileSync(file, 'utf8');
|
|
return null;
|
|
}
|
|
);
|
|
|
|
console.log(remapped);
|
|
// {
|
|
// …,
|
|
// sourcesContent: [
|
|
// 'console.log("Hello world!")',
|
|
// ],
|
|
// };
|
|
```
|
|
|
|
### Options
|
|
|
|
#### excludeContent
|
|
|
|
By default, `excludeContent` is `false`. Passing `{ excludeContent: true }` will exclude the
|
|
`sourcesContent` field from the returned sourcemap. This is mainly useful when you want to reduce
|
|
the size out the sourcemap.
|
|
|
|
#### decodedMappings
|
|
|
|
By default, `decodedMappings` is `false`. Passing `{ decodedMappings: true }` will leave the
|
|
`mappings` field in a [decoded state](https://github.com/rich-harris/sourcemap-codec) instead of
|
|
encoding into a VLQ string.
|