mirror of
https://github.com/swc-project/swc.git
synced 2024-12-18 11:11:30 +03:00
33 lines
1.0 KiB
Markdown
33 lines
1.0 KiB
Markdown
|
# Reserve `BytePos(0)` for dummy spans
|
||
|
|
|
||
|
|
- Status: accepted
|
||
|
|
- Deciders: @kdy1
|
||
|
|
- Date: 2020-05-11
|
||
|
|
|
||
|
|
## Context and Problem Statement
|
||
|
|
|
||
|
|
`BytePos(0)` was causing lots of problems because a span generated for user input can have `BytePos(0)`.
|
||
|
|
We tried various ways to distinguish the user input from synthesized spans, but all were not successful.
|
||
|
|
It especially caused various issues on source maps.
|
||
|
|
|
||
|
|
## Decision Drivers <!-- optional -->
|
||
|
|
|
||
|
|
- Source map issues, cause by `BytePos(0)`.
|
||
|
|
|
||
|
|
## Considered Options
|
||
|
|
|
||
|
|
- Adding one empty file to `SourceMap` each time we create one.
|
||
|
|
|
||
|
|
## Decision Outcome
|
||
|
|
|
||
|
|
Reserving `0` of `BytePos` provides guarantee which can be used by various codegen crates.
|
||
|
|
As `BytePos(0)` is reserved, `swc_ecma_codegen` can know if a `BytePos` is dummy without checking both of `lo` and `hi`.
|
||
|
|
|
||
|
|
### Positive Consequences
|
||
|
|
|
||
|
|
- Cleaner code, as detecting if a `BytePos` is dummy become easier.
|
||
|
|
|
||
|
|
### Adding one empty file to `SourceMap` each time we create one.
|
||
|
|
|
||
|
|
This is a code smell, and if we select this, we can't depend on the fact `BytePos(0)` is dummy.
|