Support square bracket notation in paths

CHANGELOG.md

@@ -17,7 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Don't output unparsable values ([#6469](https://github.com/tailwindlabs/tailwindcss/pull/6469))
 - Fix text decoration utilities from overriding the new text decoration color/style/thickness utilities when used with a modifier ([#6378](https://github.com/tailwindlabs/tailwindcss/pull/6378))
 - Move defaults to their own always-on layer ([#6500](https://github.com/tailwindlabs/tailwindcss/pull/6500))
-- Support negative values in safelist patterns ([6480](https://github.com/tailwindlabs/tailwindcss/pull/6480))
+- Support negative values in safelist patterns ([#6480](https://github.com/tailwindlabs/tailwindcss/pull/6480))
+- Support square bracket notation in paths ([#6519](https://github.com/tailwindlabs/tailwindcss/pull/6519))
 
 ## [3.0.2] - 2021-12-13
 

src/lib/evaluateTailwindFunctions.js

@@ -42,7 +42,7 @@ function validatePath(config, path, defaultValue) {
     ? pathToString(path)
     : path.replace(/^['"]+/g, '').replace(/['"]+$/g, '')
   const pathSegments = Array.isArray(path) ? path : toPath(pathString)
-  const value = dlv(config.theme, pathString, defaultValue)
+  const value = dlv(config.theme, pathSegments, defaultValue)
 
   if (value === undefined) {
     let error = `'${pathString}' does not exist in your theme config.`

src/util/toPath.js

@@ -1,4 +1,26 @@
+/**
+ * Parse a path string into an array of path segments.
+ *
+ * Square bracket notation `a[b]` may be used to "escape" dots that would otherwise be interpreted as path separators.
+ *
+ * Example:
+ * a -> ['a]
+ * a.b.c -> ['a', 'b', 'c']
+ * a[b].c -> ['a', 'b', 'c']
+ * a[b.c].e.f -> ['a', 'b.c', 'e', 'f']
+ * a[b][c][d] -> ['a', 'b', 'c', 'd']
+ *
+ * @param {string|string[]} path
+ **/
 export function toPath(path) {
   if (Array.isArray(path)) return path
-  return path.split(/[\.\]\[]+/g)
+
+  let openBrackets = path.split('[').length - 1
+  let closedBrackets = path.split(']').length - 1
+
+  if (openBrackets !== closedBrackets) {
+    throw new Error(`Path is invalid. Has unbalanced brackets: ${path}`)
+  }
+
+  return path.split(/\.(?![^\[]*\])|[\[\]]/g).filter(Boolean)
 }

tests/evaluateTailwindFunctions.test.js

@@ -31,6 +31,111 @@ test('it looks up values in the theme using dot notation', () => {
   })
 })
 
+test('it looks up values in the theme using bracket notation', () => {
+  let input = css`
+    .banana {
+      color: theme('colors[yellow]');
+    }
+  `
+
+  let output = css`
+    .banana {
+      color: #f7cc50;
+    }
+  `
+
+  return run(input, {
+    theme: {
+      colors: {
+        yellow: '#f7cc50',
+      },
+    },
+  }).then((result) => {
+    expect(result.css).toEqual(output)
+    expect(result.warnings().length).toBe(0)
+  })
+})
+
+test('it looks up values in the theme using consecutive bracket notation', () => {
+  let input = css`
+    .banana {
+      color: theme('colors[yellow][100]');
+    }
+  `
+
+  let output = css`
+    .banana {
+      color: #f7cc50;
+    }
+  `
+
+  return run(input, {
+    theme: {
+      colors: {
+        yellow: {
+          100: '#f7cc50',
+        },
+      },
+    },
+  }).then((result) => {
+    expect(result.css).toEqual(output)
+    expect(result.warnings().length).toBe(0)
+  })
+})
+
+test('it looks up values in the theme using bracket notation that have dots in them', () => {
+  let input = css`
+    .banana {
+      padding-top: theme('spacing[1.5]');
+    }
+  `
+
+  let output = css`
+    .banana {
+      padding-top: 0.375rem;
+    }
+  `
+
+  return run(input, {
+    theme: {
+      spacing: {
+        '1.5': '0.375rem',
+      },
+    },
+  }).then((result) => {
+    expect(result.css).toEqual(output)
+    expect(result.warnings().length).toBe(0)
+  })
+})
+
+test('theme with mismatched brackets throws an error ', async () => {
+  let config = {
+    theme: {
+      spacing: {
+        '1.5': '0.375rem',
+      },
+    },
+  }
+
+  let input = (path) => css`
+    .banana {
+      padding-top: theme('${path}');
+    }
+  `
+
+  await expect(run(input('spacing[1.5]]'), config)).rejects.toThrowError(
+    `Path is invalid. Has unbalanced brackets: spacing[1.5]]`
+  )
+
+  await expect(run(input('spacing[[1.5]'), config)).rejects.toThrowError(
+    `Path is invalid. Has unbalanced brackets: spacing[[1.5]`
+  )
+
+  await expect(run(input('spacing[a['), config)).rejects.toThrowError(
+    `Path is invalid. Has unbalanced brackets: spacing[a[`
+  )
+})
+
 test('color can be a function', () => {
   let input = css`
     .backgroundColor {

tests/to-path.test.js

@@ -7,11 +7,12 @@ it('should keep an array as an array', () => {
 })
 
 it.each`
-  input         | output
-  ${'a.b.c'}    | ${['a', 'b', 'c']}
-  ${'a[0].b.c'} | ${['a', '0', 'b', 'c']}
-  ${'.a'}       | ${['', 'a']}
-  ${'[].a'}     | ${['', 'a']}
+  input             | output
+  ${'a.b.c'}        | ${['a', 'b', 'c']}
+  ${'a[0].b.c'}     | ${['a', '0', 'b', 'c']}
+  ${'.a'}           | ${['a']}
+  ${'[].a'}         | ${['a']}
+  ${'a[1.5][b][c]'} | ${['a', '1.5', 'b', 'c']}
 `('should convert "$input" to "$output"', ({ input, output }) => {
   expect(toPath(input)).toEqual(output)
 })