@warn

在编写 混入 和 函数 时，你可能希望阻止用户传递某些参数或某些值。他们可能会传递现在已弃用的旧参数，或者他们可能会以不太理想的方式调用你的 API。

@warn 规则就是为此而设计的。它被写为 @warn <expression>，并为用户打印 表达 的值（通常是一个字符串），以及指示如何调用当前 mixin 或函数的堆栈跟踪。但与 @error 规则 不同的是，它并不能完全阻止 Sass。

¥The @warn rule is designed just for that. It’s written @warn <expression> and it prints the value of the expression (usually a string) for the user, along with a stack trace indicating how the current mixin or function was called. Unlike the @error rule, though, it doesn’t stop Sass entirely.

SCSS Syntax

$known-prefixes: webkit, moz, ms, o;

@mixin prefix($property, $value, $prefixes) {
  @each $prefix in $prefixes {
    @if not index($known-prefixes, $prefix) {
      @warn "Unknown prefix #{$prefix}.";
    }

    -#{$prefix}-#{$property}: $value;
  }
  #{$property}: $value;
}

.tilt {
  // Oops, we typo'd "webkit" as "wekbit"!
  @include prefix(transform, rotate(15deg), wekbit ms);
}

Sass Syntax

$known-prefixes: webkit, moz, ms, o

@mixin prefix($property, $value, $prefixes)
  @each $prefix in $prefixes
    @if not index($known-prefixes, $prefix)
      @warn "Unknown prefix #{$prefix}."


    -#{$prefix}-#{$property}: $value

  #{$property}: $value


.tilt
  // Oops, we typo'd "webkit" as "wekbit"!
  @include prefix(transform, rotate(15deg), wekbit ms)

CSS Output

.tilt {
  -wekbit-transform: rotate(15deg);
  -ms-transform: rotate(15deg);
  transform: rotate(15deg);
}

警告和堆栈跟踪的确切格式因实现而异。这就是 Dart Sass 中的样子：

¥The exact format of the warning and stack trace varies from implementation to implementation. This is what it looks like in Dart Sass:

Warning: Unknown prefix wekbit.
    example.scss 6:7   prefix()
    example.scss 16:3  root stylesheet