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65 lines
1.9 KiB
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65 lines
1.9 KiB
Plaintext
---
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title: "Breaking Change: Strict Unary Operators"
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introduction: >
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Sass has historically allowed `-` and `+` to be used in ways that make it
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ambiguous whether the author intended them to be a binary or unary operator.
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This confusing syntax is being deprecated.
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---
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How is this property compiled?
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<% example(autogen_css: false) do %>
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$size: 10px;
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div {
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margin: 15px -$size;
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}
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===
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$size: 10px
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div
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margin: 15px -$size
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<% end %>
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Some users might say "the `-` is attached to `$size`, so it should be `margin:
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20px -10px`". Others might say "the `-` is between `20px` and `$size`, so it
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should be `margin: 5px`." Sass currently agrees with the latter opinion, but the
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real problem is that it's so confusing in the first place! This is a natural but
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unfortunate consequence of CSS's space-separated list syntax combined with
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Sass's arithmetic syntax.
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That's why we're moving to make this an error. In the future, if you want to use
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a binary `-` or `+` operator (that is, one that subtracts or adds two numbers),
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you'll need to put whitespace on both sides or on neither side:
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* Valid: `15px - $size`
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* Valid: `(15px)-$size`
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* Invalid: `15px -$size`
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If you want to use a unary `-` or `+` operator as part of a space-separated
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list, you'll (still) need to wrap it in parentheses:
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* Valid: `15px (-$size)`
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## Transition Period
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<% impl_status dart: '1.55.0', libsass: false, ruby: false %>
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We'll make this an error in Dart Sass 2.0.0, but until then it'll just emit a
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deprecation warning.
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<%= partial '../snippets/silence-deprecations' %>
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## Automatic Migration
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You can use [the Sass migrator] to automatically update your stylesheets to add
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a space after any `-` or `+` operators that need it, which will preserve the
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existing behavior of these stylesheets.
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[the Sass migrator]: https://github.com/sass/migrator#readme
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```shellsession
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$ npm install -g sass-migrator
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$ sass-migrator strict-unary **/*.scss
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```
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