[Bug]: postcss-convert-values stripping % from 0 in initial-value for @property at-rule

[dougwollison]

Describe the bug

I'm trying to define the syntax for a css custom property using @property.

@property --percentage {
	inherits: false;
	initial-value: 0%;
	syntax: '<percentage>';
}

This is so I can animate the value of the custom property. However, it's failing due to the convert-values plugin stripping the % sign. Haven't been able to work around this, initial-value needs to be declared for this to work.

Expected behaviour

Output should leave initial-value untouched.

Steps to reproduce

Include the mentioned code in a stylesheet and compile using the default or advanced presets. The output will strip the % unit.

Version

6.0.1

Preset

default

Environment

System:
    OS: Linux 4.4 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
    CPU: (8) x64 Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz
    Memory: 12.21 GB / 31.96 GB
    Container: Yes
    Shell: 5.1.4 - /bin/bash

Package details

├─┬ autoprefixer@10.4.16
│ └── postcss@8.4.31 deduped        
├─┬ cssnano@6.0.1
│ ├─┬ cssnano-preset-default@6.0.1  
│ │ ├─┬ css-declaration-sorter@6.4.1
│ │ │ └── postcss@8.4.31 deduped    
│ │ ├─┬ cssnano-utils@4.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-calc@9.0.1
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-colormin@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-convert-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-comments@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-duplicates@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-empty@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-overridden@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-merge-longhand@6.0.0
│ │ │ ├── postcss@8.4.31 deduped
│ │ │ └─┬ stylehacks@6.0.0
│ │ │   └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-merge-rules@6.0.1
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-font-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-gradients@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-params@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-selectors@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-charset@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-display-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-positions@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-repeat-style@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-string@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-timing-functions@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-unicode@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-url@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-whitespace@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-ordered-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-reduce-initial@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-reduce-transforms@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-svgo@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-unique-selectors@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
├─┬ gulp-postcss@9.0.1
│ ├─┬ postcss-load-config@3.1.4
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
├─┬ gulp-sourcemaps@3.0.0
│ └─┬ @gulp-sourcemaps/identity-map@2.0.1
│   └── postcss@7.0.39
├─┬ postcss-csso@6.0.1
│ └── postcss@8.4.31 deduped
├─┬ postcss-preset-env@9.1.4
│ ├─┬ @csstools/postcss-cascade-layers@4.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-color-function@3.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-color-mix-function@2.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-exponential-functions@1.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-font-format-keywords@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-gradients-interpolation-method@4.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-hwb-function@3.0.5
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-ic-unit@3.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-initial@1.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-is-pseudo-class@4.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-float-and-clear@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-resize@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-viewport-units@2.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-media-minmax@1.1.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-media-queries-aspect-ratio-number-values@2.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-nested-calc@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-normalize-display-values@3.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-oklab-function@3.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-progressive-custom-properties@3.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-relative-color-syntax@2.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-scope-pseudo-class@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-stepped-value-functions@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-text-decoration-shorthand@3.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-trigonometric-functions@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-unset-value@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-blank-pseudo@6.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-has-pseudo@6.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-prefers-color-scheme@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-attribute-case-insensitive@6.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-clamp@4.1.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-functional-notation@6.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-hex-alpha@9.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-rebeccapurple@9.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-media@10.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-properties@13.3.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-selectors@7.1.5
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-dir-pseudo-class@8.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-double-position-gradients@5.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-focus-visible@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-focus-within@8.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-font-variant@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-gap-properties@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-image-set-function@6.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-lab-function@6.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-logical@7.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-nesting@12.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-opacity-percentage@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-overflow-shorthand@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-page-break@3.0.4
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-place@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-pseudo-class-any-link@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-replace-overflow-wrap@4.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-selector-not@7.0.1
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
└── postcss@8.4.31

Additional context

No response

[xiaojundebug]

I created a PR, but I don't know how to merge it.

#1531