Embedding · Source maps

lessish emits Source Maps v3, matching less.js's output. There are two ways to ask for one.

compile_with_source_map

The dedicated entry point returns a SourceMapResult with the CSS, the map JSON, and the annotation URL split apart:

import json
from lessish import Lessish

ls = Lessish()
result = ls.compile_with_source_map(
    '.a { color: red; }',
    filename='styles.less',
    source_map={'outputSourceFiles': True},
)

# CSS, with the trailing /*# sourceMappingURL=… */ annotation.
result.css
# => '.a {\n  color: red;\n}\n/*# sourceMappingURL=styles.css.map */'

# The URL embedded in that annotation.
result.annotation_url
# => 'styles.css.map'

# The Source Maps v3 JSON, as a string.
document = json.loads(result.map_json)
assert document['version'] == 3
assert document['file'] == 'styles.css'
assert document['sources'] == ['styles.less']
# outputSourceFiles=True inlines the original Less into sourcesContent.
assert 'sourcesContent' in document

source_map accepts the same options dict less.js does — for example outputSourceFiles, sourceMapURL, sourceMapBasepath, sourceMapRootpath. Pass source_map=True for defaults.

Via compile(source_map=…)

compile also accepts source_map; when set, it returns the CSS string with the annotation appended (the same result.css as above), without the separate map JSON. Use compile_with_source_map when you need the map file itself.

from lessish import Lessish

css = Lessish().compile('.a { color: red; }', filename='styles.less', source_map=True)
assert css.endswith('/*# sourceMappingURL=styles.css.map */')

SourceMapResult fields

Field	Type	Meaning
css	str	CSS with the trailing sourceMappingURL annotation.
map_json	str	The Source Maps v3 document, serialised.
annotation_url	str	The URL embedded in the annotation comment.

Writing the two artifacts to disk is exactly what the CLI's --source-map / --source-map-out flags do — see ../cli.md.

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