Summary:
Introduces a new mechanism to build source maps that allows us to use real mapping segments instead of just mapping line-by-line.
This mechanism is only used when building development bundles to improve the debugging experience in Chrome.
The new mechanism takes advantage of a new feature in babel-generator that exposes raw mapping objects. These raw mapping objects are converted to arrays with 2, 4, or 5 for the most compact representation possible.
We no longer generate a source map for the bundle that maps each line to itself in conjunction with configuring babel generator to retain lines.
Instead, we create a source map with a large mappings object produced from the mappings of each individual file in conjunction with a “carry over” – the number of preceding lines in the bundle.
The implementation makes a couple of assumptions that hold true for babel transform results, e.g. mappings being in the order of the generated code, and that a block of mappings always belongs to the same source file. In addition, the implementation avoids allocation of objects and strings at all costs. All calculations are purely numeric, and base64 vlq produces numeric ascii character codes. These are written to a preallocated buffer objects, which is turned to a string only at the end of the building process. This implementation is ~5x faster than using the source-map library.
In addition to providing development source maps that work better, we can now also produce individual high-quality source maps for production builds and combine them to an “index source map”. This approach is unfeasable for development source maps, because index source map consistently crash Chrome.
Better production source maps are useful to get precise information about source location and symbol names when symbolicating stack traces from crashes in production.
Reviewed By: jeanlauliac
Differential Revision: D4382290
fbshipit-source-id: 365a176fa142729d0a4cef43edeb81084361e54d
Summary: Adds flow types for output functionality for easier maintenance and interop with new code
Reviewed By: matryoshcow
Differential Revision: D4211863
fbshipit-source-id: 591407d3a6d49536054ae94ba31125c18a1e1fa1
Summary:
Adds the possibility to specify an array of files (group roots) that are used to bundle modules outside of the “startup section” into bigger groups by colocating their code.
A require call for any grouped module will load all modules in that group.
Files contained by multiple groups are deoptimized (i.e. bundled as individual script)
Reviewed By: martinbigio
Differential Revision: D3841780
fbshipit-source-id: 8d37782792efd66b5f557c7567489f68c9b229d8
Summary:This adds support for source maps that can be used for “random access modules” / “unbundles”
- source maps contain an extra custom field: `x_facebook_offsets`
- this field maps module IDs to line offsets
- the source map is built as if all files were concatenated
Decoding/symbolication works as follows:
- when decoding a stack trace, and a stack frame comes from a filename that contains only numbers and ends with `.js`, look up the additionally needed line offset in the offset map and add it to the original line of the stack frame.
- consume the source map as usual
Reviewed By: martinbigio
Differential Revision: D3072426
fb-gh-sync-id: 827e6dc13b1959f02903baafa7f9e4fc2e0d4bb9
shipit-source-id: 827e6dc13b1959f02903baafa7f9e4fc2e0d4bb9
