Define how to extract the sourceMappingURL comment
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JavaScript, CSS and WebAssembly sources. It defines multiple ways to do so: either by actually parsing the code, or by just going through all the lines of the program looking for what "looks like" a comment. This is so that different implementations can choose what's best for them, depending on whether they are already parsing the code or not. To ensure consist behavior accross implementations that choose different strategies, the specification enforces additional requirements on tools that append a `sourceMappingURL` comment to the generated code: the comment must be placed in such a way that all extraction methods yield the same result. This is not an unresonable burden, since if the progeram is syntactically valid, simply adding the comment at the end of the file only potentially followed by other tool-injected comments is enough. This requirement is lifted if the input code given to the tool is already "maliciously crafted", since we would otherwise require tool to go rewrite that code (for example, splitting strings that contain something that looks like a comment). I have left the CSS extraction method as TODO because first I want to check how do you feel about the JS one. It has the following properties: - It iterates line by line. Implementations can thus optimize it by going through each line _in reverse order_, and then scanning through its characters from the beginning to the end (which is what a regexp would do). - It expects multi-line comments to actually be in a single line. - It returns the last `sourceMappingURL` comment (or well, comment-like) found in the source. - It only considers comments after the last piece of code (i.e. it discards any comment found so far every time it sees some non-comment non-whitespace characters). - It has no requirements about what is _before_ a comment. Adding the comment at the end of the file without first ensuring that there is a newline before it is valid.
nicolo-ribaudo
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Jun 13, 2024
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| 1. [=Collect a sequence of code points=] that are [=white space code points|ECMAScript | ||
| white space code points=] from |line| given |position|. |
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In the original PR there was this comment by @gibson042:
Is it a problem that ECMAScript white space is subject to change over time as future Unicode editions change the set of code points in general category "Space_Separator"?
I think it's ok to expect implementations to evolve together with Unicode, but how do other folks feel?
jkup
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Jun 25, 2024
takikawa
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jkup
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gibson042
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Jul 14, 2024
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| ### Linking through HTTP headers | ||
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| If a file is served through HTTP(S) with a `sourcemap` header, the value of the header is | ||
| the URL of the linked source map. | ||
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| ``` | ||
| sourcemap: <url> | ||
| ``` | ||
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| Note: Previous revisions of this document recommended a header name of `x-sourcemap`. This | ||
| is now deprecated; `sourcemap` is now expected. |
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Some [belated] observations:
- The most precise vocabulary is "[HTTP] header field" per RFC 9110; should that be adopted in this document or should it stick with the colloquial "header"?
sourcemapreally should be registered in Message Headers, but is currently not.- Is
<url>valid and meaningful? For a more precise and analogous definition, see RFC 8288.
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This was originally opened at tc39/source-map-spec#30
I am currently being hand-wavy about CSS, only saying "it should be similar to JS". I can propose the adjusted algorithm in a followup, but given that technically source maps are not language-specific we might also just say "other text languages should be like JS, adapted to their own comments syntax".
This patch explicitly defines how to extract such comments from JavaScript, CSS and WebAssembly sources.
It defines multiple ways to do so: either by actually parsing the code, or by just going through all the lines of the program looking for what "looks like" a comment. This is so that different implementations can choose what's best for them, depending on whether they are already parsing the code or not.
To ensure consist behavior accross implementations that choose different strategies, the specification enforces additional requirements on tools that append a
sourceMappingURLcomment to the generated code: the comment must be placed in such a way that all extraction methods yield the same result. This is not an unresonable burden, since if the progeram is syntactically valid, simply adding the comment at the end of the file only potentially followed by other tool-injected comments is enough. This requirement is lifted if the input code given to the tool is already "maliciously crafted", since we would otherwise require tool to go rewrite that code (for example, splitting strings that contain something that looks like a comment).It has the following properties:
sourceMappingURLcomment (or well, comment-like) found in the source.