feat: Adds negative z-index rule to stylelint (#4)

src/stylelint/__tests__/z-index-value-constraint.test.js

@@ -0,0 +1,63 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import { describe, test, expect } from "vitest";
+import stylelint from "stylelint";
+
+import { configBasedir } from "./common.js";
+
+// This is for prettier format: https://github.com/prettier/prettier/issues/2330
+// String.raw is an identity function in this context
+const css = String.raw;
+
+function runPlugin(code) {
+  return stylelint.lint({
+    code,
+    configBasedir,
+    config: {
+      plugins: ["../z-index-value-constraint.js"],
+      rules: {
+        "@cloudscape-design/z-index-value-constraint": [true],
+      },
+    },
+  });
+}
+
+describe("z-index value contstraint rule", () => {
+  test("allows non integer z-index values", async () => {
+    const result = await runPlugin(css`
+      .styled-circle-motion {
+        @include styles.with-motion {
+          z-index: some.$variable;
+        }
+      }
+    `);
+
+    expect(result.errored).toBe(false);
+  });
+
+  test.each([0, 1000])("allows non negative z-index values: %s", async zIndexValue => {
+    const result = await runPlugin(css`
+      .styled-circle-motion {
+        @include styles.with-motion {
+          z-index: ${zIndexValue};
+        }
+      }
+    `);
+
+    expect(result.errored).toBe(false);
+  });
+
+  test("does not allow negative z-index values", async () => {
+    const result = await runPlugin(css`
+      .styled-circle-motion {
+        @include styles.with-motion {
+          z-index: -10;
+        }
+      }
+    `);
+
+    expect(result.errored).toBe(true);
+    expect(result.results[0].warnings[0].text).toBe(`Avoid using negative z-index values: -10.
+    This can cause the element to disappear behind its container's background color. (@cloudscape-design/z-index-value-constraint)`);
+  });
+});

src/stylelint/index.js

@@ -3,5 +3,6 @@
 import licenseHeaders from "./license-headers.js";
 import noImplicitDescendant from "./no-implicit-descendant.js";
 import noMotionOutsideOfMixin from "./no-motion-outside-of-mixin.js";
+import zIndexValueConstraint from "./z-index-value-constraint.js";
 
-export default [noImplicitDescendant, noMotionOutsideOfMixin, licenseHeaders];
+export default [noImplicitDescendant, noMotionOutsideOfMixin, licenseHeaders, zIndexValueConstraint];

src/stylelint/z-index-value-constraint.js

@@ -0,0 +1,43 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import stylelint from "stylelint";
+
+const ruleName = "@cloudscape-design/z-index-value-constraint";
+
+const messages = stylelint.utils.ruleMessages(ruleName, {
+  noNegativeZIndex: zIndexValue => {
+    return `Avoid using negative z-index values: ${zIndexValue}.
+    This can cause the element to disappear behind its container's background color.`;
+  },
+});
+
+function zIndexValueConstraint(enabled) {
+  if (!enabled) {
+    return;
+  }
+
+  return function (root, result) {
+    root.walkDecls(function (decl) {
+      if (decl.prop !== "z-index") return;
+
+      const zIndexValue = Number(decl.value);
+
+      // If the z-index value is not a number (e.g. variable), don't throw an error.
+      if (Number.isNaN(zIndexValue)) return;
+
+      if (zIndexValue < 0) {
+        stylelint.utils.report({
+          result,
+          ruleName,
+          message: messages.noNegativeZIndex(zIndexValue),
+          node: decl,
+        });
+      }
+    });
+  };
+}
+
+zIndexValueConstraint.ruleName = ruleName;
+zIndexValueConstraint.messages = messages;
+
+export default stylelint.createPlugin(ruleName, zIndexValueConstraint);