Update: Correctly indent JSXText with trailing linebreaks (fixes #9878) (#10055)

This fixes a bug in the `indent` rule where a line comparison with the end of a token would use the end location of any trailing whitespace in the token, rather than the location of the last non-whitespace character in the token. This behavior went against user intuition for tokens with trailing whitespace.

Author: not-an-aardvark

lib/rules/indent.js

@@ -779,6 +779,19 @@ module.exports = {
             return (statement.type === "ExpressionStatement" || statement.type === "VariableDeclaration") && statement.parent.type === "Program";
         }
 
+        /**
+         * Counts the number of linebreaks that follow the last non-whitespace character in a string
+         * @param {string} string The string to check
+         * @returns {number} The number of JavaScript linebreaks that follow the last non-whitespace character,
+         * or the total number of linebreaks if the string is all whitespace.
+         */
+        function countTrailingLinebreaks(string) {
+            const trailingWhitespace = string.match(/\s*$/)[0];
+            const linebreakMatches = trailingWhitespace.match(astUtils.createGlobalLinebreakMatcher());
+
+            return linebreakMatches === null ? 0 : linebreakMatches.length;
+        }
+
         /**
          * Check indentation for lists of elements (arrays, objects, function params)
          * @param {ASTNode[]} elements List of elements that should be offset
@@ -836,8 +849,12 @@ module.exports = {
                 } else {
                     const previousElement = elements[index - 1];
                     const firstTokenOfPreviousElement = previousElement && getFirstToken(previousElement);
+                    const previousElementLastToken = previousElement && sourceCode.getLastToken(previousElement);
 
-                    if (previousElement && sourceCode.getLastToken(previousElement).loc.end.line > startToken.loc.end.line) {
+                    if (
+                        previousElement &&
+                        previousElementLastToken.loc.end.line - countTrailingLinebreaks(previousElementLastToken.value) > startToken.loc.end.line
+                    ) {
                         offsets.setDesiredOffsets(element.range, firstTokenOfPreviousElement, 0);
                     }
                 }

tests/lib/rules/indent.js

@@ -4607,6 +4607,16 @@ ruleTester.run("indent", rule, {
                     );
                 }
             `,
+        unIndent`
+            <div>foo
+                <div>bar</div>
+            </div>
+        `,
+        unIndent`
+            <small>Foo bar&nbsp;
+                <a>baz qux</a>.
+            </small>
+        `,
         {
             code: unIndent`
                 a(b
@@ -9136,6 +9146,32 @@ ruleTester.run("indent", rule, {
             `,
             errors: expectedErrors([3, 8, 6, "Block"])
         },
+        {
+            code: unIndent`
+                <div>foo
+                <div>bar</div>
+                </div>
+            `,
+            output: unIndent`
+                <div>foo
+                    <div>bar</div>
+                </div>
+            `,
+            errors: expectedErrors([2, 4, 0, "Punctuator"])
+        },
+        {
+            code: unIndent`
+                <small>Foo bar&nbsp;
+                <a>baz qux</a>.
+                </small>
+            `,
+            output: unIndent`
+                <small>Foo bar&nbsp;
+                    <a>baz qux</a>.
+                </small>
+            `,
+            errors: expectedErrors([2, 4, 0, "Punctuator"])
+        },
         {
             code: unIndent`
                 ({