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node_modules/stylelint/lib/rules/function-linear-gradient-no-nonstandard-direction/README.md

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+# function-linear-gradient-no-nonstandard-direction
+
+Disallow direction values in `linear-gradient()` calls that are not valid according to the
+[standard syntax](https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient#Syntax).
+
+```css
+.foo { background: linear-gradient(to top, #fff, #000); }
+/**                                ↑
+ * This (optional) first argument is the "direction" */
+```
+
+A valid and standard direction value is one of the following:
+
+-   an angle
+-   `to ` plus a side-or-corner (`to top`, `to bottom`, `to left`, `to right`; `to top right`, `to right top`, `to bottom left`, etc.)
+
+A common mistake (matching outdated non-standard syntax) is to use just a side-or-corner without the preceding `to`.
+
+## Options
+
+### `true`
+
+The following patterns are considered warnings:
+
+```css
+.foo { background: linear-gradient(top, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(bottom, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(left, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(45, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(to top top, #fff, #000); }
+```
+
+The following patterns are *not* considered warnings:
+
+```css
+.foo { background: linear-gradient(to top, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(to bottom right, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(45deg, #fff, #000); }
+```
+
+```css
+.foo { background: linear-gradient(1.57rad, #fff, #000); }
+```
+
+```css
+/* Direction defaults to "to bottom" */
+.foo { background: linear-gradient(#fff, #000); }
+```

node_modules/stylelint/lib/rules/function-linear-gradient-no-nonstandard-direction/index.js

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+"use strict"
+
+const functionArgumentsSearch = require("../../utils/functionArgumentsSearch")
+const report = require("../../utils/report")
+const ruleMessages = require("../../utils/ruleMessages")
+const validateOptions = require("../../utils/validateOptions")
+const postcss = require("postcss")
+
+const ruleName = "function-linear-gradient-no-nonstandard-direction"
+
+const messages = ruleMessages(ruleName, {
+  rejected: "Unexpected nonstandard direction",
+})
+
+function isStandardDirection(source, withToPrefix) {
+  const regexp = withToPrefix ? /^to (top|left|bottom|right)(?: (top|left|bottom|right))?$/ : /^(top|left|bottom|right)(?: (top|left|bottom|right))?$/
+
+  const matches = source.match(regexp)
+  if (!matches) {
+    return false
+  }
+  if (matches.length === 2) {
+    return true
+  }
+  // Cannot repeat side-or-corner, e.g. "to top top"
+  if (matches.length === 3 && matches[1] !== matches[2]) {
+    return true
+  }
+  return false
+}
+
+const rule = function (actual) {
+  return (root, result) => {
+    const validOptions = validateOptions(result, ruleName, { actual })
+    if (!validOptions) {
+      return
+    }
+
+    root.walkDecls(decl => {
+      functionArgumentsSearch(decl.toString().toLowerCase(), "linear-gradient", (expression, expressionIndex) => {
+        const firstArg = expression.split(",")[0].trim()
+
+        // If the first character is a number, we can assume the user intends an angle
+        if (/[\d\.]/.test(firstArg[0])) {
+          if (/^[\d\.]+(?:deg|grad|rad|turn)$/.test(firstArg)) {
+            return
+          }
+          complain()
+          return
+        }
+
+        // The first argument may not be a direction: it may be an angle,
+        // or a color stop (in which case user gets default direction, "to bottom")
+        // cf. https://drafts.csswg.org/css-images-3/#linear-gradient-syntax
+        if (!/left|right|top|bottom/.test(firstArg)) {
+          return
+        }
+
+        const withToPrefix = !postcss.vendor.prefix(decl.value)
+        if (!isStandardDirection(firstArg, withToPrefix)) {
+          complain()
+          return
+        }
+
+        function complain() {
+          report({
+            message: messages.rejected,
+            node: decl,
+            index: expressionIndex,
+            result,
+            ruleName,
+          })
+        }
+      })
+    })
+  }
+}
+
+rule.ruleName = ruleName
+rule.messages = messages
+module.exports = rule