https://github.com/meteor/meteor/issues/10112#issuecomment-428646872
Further down in the mergeCss function, when we call CssTools.stringifyCss,
we pass the following option:
// don't try to read the referenced sourcemaps from the input
inputSourcemaps: false
Apparently this isn't enough to avoid reading inline source maps from the
input file, so we should be a bit more aggressive about preventing postcss
from picking up inline source maps.
This change mostly affects .css files imported from node_modules, and
possibly raw .css files in the application that happen to have inline
sourceMappingURL= comments. For CSS output from compiler plugins like LESS
and SCSS, we have a totally different mechanism of handling source maps,
namely file.getSourceMap().
Should fix#10112.
The previous implementation had a run time quadratic in the number of CSS files with an associated source map. This new implementation has a linear run time because it iterates only once through all mappings of each CSS file.
We shouldn't be processing .css files on the server anyway, because of a
similar restriction in packages/meteor/plugin/basic-file-types.js, but
it seemed wise to enforce that restriction redundantly here.
