Add a decoding algorithm for index maps #132
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takikawa
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Sep 27, 2024
takikawa
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Sep 27, 2024
source-map.bs
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| 1. If |offsetColumn| is not a number, [=optionally report an error=]. | ||
| 1. If |previousOffset| is not null, | ||
| 1. If |previousLastMapping| is not null, | ||
| 1. If |offsetLine| is less than |previousLastMapping|'s [=decoded mapping/generatedLine=], [=optionally report an error=]. |
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Should these range checks be "less than or equal to" to be strict inequality rather than allowing equality?
takikawa
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Sep 27, 2024
jkrems
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jridgewell
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jridgewell
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Could you rebase? :) |
These aren't linked to so they don't need the tags
* Fix first line issue * Use extend again for new mappings
* Check the overlap of ranges {lastFirst, lastPrev} and the
{first, last} of the current source map section instead of
current more complicated steps.
* The overlap check also ensures the order of the ranges, beyond
the ordering of the offsets (which itself doesn't guarantee
range order)
* Some editorial changes for the check
Also set a default value so the algorithm continues
An implementation may do a generated->original lookup in an index map
by first searching through the sections by their offset and looking in
only the section where the position is within the range {offset, nextOffset}.
This is only valid if all mappings in a given section are contained in
that range, rather than going into the next section's range.
Also simplifies the check by removing the firstPreviousMapping variable
and its use.
The algorithm checks that the
(1) the offsets are ordered (in 8g)
(2) the last mapping of the previous section is before the
current offset (in 8h)
(3) it doesn't check that the first mapping is after the
current offset because that is true by construction
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I rebased this and made some adjustments. It now checks that mapping ranges are always contained within the section offsets too, which I think is required for the assumptions made in implementations about mappings appearing in a unique bucket. That means mappings are ordered like this: and so on. |
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Rendered draft
This PR adds a decoding algorithm for index maps along the lines of the existing algorithms for normal source maps.
I'll leave a few comments for cases in the spec where it's not clear what we should do: