[Bug]: Sass plugin does not compile styles for compound selectors containing ::v-deep/:deep()

[mietl]

Version

System:
    OS: macOS 15.5
    CPU: (8) arm64 Apple M2
    Memory: 1.23 GB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Browsers:
    Chrome: 137.0.7151.120
    Safari: 18.5
  npmPackages:
    @rsbuild/core: ^1.3.22 => 1.3.22 
    @rsbuild/plugin-sass: ^1.3.2 => 1.3.2 
    @rsbuild/plugin-vue2: ^1.0.3 => 1.0.3

Details

When using ‎@rsbuild/plugin-sass, styles for compound selectors that include ‎::v-deep are missing in the compiled CSS output. This happens when ‎::v-deep is used together with other class selectors in a compound selector.

Reproduce link

https://codesandbox.io/p/github/rspack-contrib/rsbuild-codesandbox-example/csb-k44dnf/draft/happy-goldberg

Reproduce Steps

Steps to Reproduce:

1. Use a compound selector with repeated class names in a ‎.scss file, for example:

.b{
   font-size: 21px
}
.b, .from deep(.a){
  color: red;
}

2. Check the compiled CSS output.

[mietl]

When there are repeated class names, only one compound selector appears in the compiled output.

[thinkasany]

https://rsbuild.rs/guide/styling/css-usage#lightning-css

It seems to be a Lightning-related issue. When I use tools: { lightningcssLoader: false }, it doesn't seem to have this problem.

before:

.el-form-item[data-v-17c684c8] {
  border: 1px solid red;
  height: 400px;
  padding: 20px;
}
.el-form-item[data-v-17c684c8] .el-form-item__content {
  height: 100%;
}
.t-textarea[data-v-17c684c8] {
  white-space: pre-wrap;
  word-wrap: break-word;
  white-space: pre-wrap;
  word-wrap: break-word;
  height: 100% !important;
}

after:

.el-form-item[data-v-17c684c8] {
  border: 1px solid red;
  height: 400px;
  padding: 20px;
}
.el-form-item[data-v-17c684c8] .el-form-item__content {
  height: 100%;
}
.t-textarea[data-v-17c684c8] {
  white-space: pre-wrap;
  word-wrap: break-word;
}
.t-textarea[data-v-17c684c8],
.t-textarea[data-v-17c684c8] .el-textarea__inner {
  white-space: pre-wrap;
  word-wrap: break-word;
  height: 100% !important;
}

[mietl]

https://rsbuild.rs/guide/styling/css-usage#lightning-css

It seems to be a Lightning-related issue. When I use tools: { lightningcssLoader: false }, it doesn't seem to have this problem.

I appreciate your help in pinpointing the cause!