[Fix] no-this-in-sfc, component detection: Improve stateless component detection

Fixes #3054.

Author: Wesitos

CHANGELOG.md

@@ -5,6 +5,11 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 
 ## Unreleased
 
+### Fixed
+* [`no-this-in-sfc`], component detection: Improve stateless component detection ([#3056][] @Wesitos)
+
+[#3056]: https://github.com/yannickcr/eslint-plugin-react/pull/3056
+
 ## [7.25.0] - 2021.08.27
 
 ### Added

lib/util/Components.js

@@ -608,6 +608,7 @@ function componentRule(rule, context) {
      * @returns {ASTNode | undefined}
      */
     getStatelessComponent(node) {
+      const parent = node.parent;
       if (
         node.type === 'FunctionDeclaration'
         && (!node.id || isFirstLetterCapitalized(node.id.name))
@@ -617,6 +618,13 @@ function componentRule(rule, context) {
       }
 
       if (node.type === 'FunctionExpression' || node.type === 'ArrowFunctionExpression') {
+        const isMethod = parent.type === 'Property' && parent.method;
+        const isPropertyAssignment = parent.type === 'AssignmentExpression'
+          && parent.left.type === 'MemberExpression';
+        const isModuleExportsAssignment = isPropertyAssignment
+          && parent.left.object.name === 'module'
+          && parent.left.property.name === 'exports';
+
         if (node.parent.type === 'ExportDefaultDeclaration') {
           if (utils.isReturningJSX(node)) {
             return node;
@@ -630,31 +638,38 @@ function componentRule(rule, context) {
           }
           return undefined;
         }
-        if (utils.isInAllowedPositionForComponent(node) && utils.isReturningJSXOrNull(node)) {
-          if (utils.isParentComponentNotStatelessComponent(node)) return undefined;
 
-          const isMethod = node.parent.type === 'Property' && node.parent.method;
+        // Case like `React.memo(() => <></>)` or `React.forwardRef(...)`
+        const pragmaComponentWrapper = utils.getPragmaComponentWrapper(node);
+        if (pragmaComponentWrapper) {
+          return pragmaComponentWrapper;
+        }
 
-          if (isMethod && !isFirstLetterCapitalized(node.parent.key.name)) {
-            return utils.isReturningJSX(node) ? node : undefined;
-          }
+        if (!(utils.isInAllowedPositionForComponent(node) && utils.isReturningJSXOrNull(node))) {
+          return undefined;
+        }
 
-          if (node.id && isFirstLetterCapitalized(node.id.name)) {
-            return node;
-          }
+        if (utils.isParentComponentNotStatelessComponent(node)) {
+          return undefined;
+        }
 
-          if (!node.id) {
-            return node;
-          }
+        if (isMethod && !isFirstLetterCapitalized(node.parent.key.name)) {
+          return utils.isReturningJSX(node) ? node : undefined;
+        }
 
-          return undefined;
+        if (node.id) {
+          return isFirstLetterCapitalized(node.id.name) ? node : undefined;
         }
 
-        // Case like `React.memo(() => <></>)` or `React.forwardRef(...)`
-        const pragmaComponentWrapper = utils.getPragmaComponentWrapper(node);
-        if (pragmaComponentWrapper) {
-          return pragmaComponentWrapper;
+        if (
+          isPropertyAssignment
+          && !isModuleExportsAssignment
+          && !isFirstLetterCapitalized(parent.left.property.name)
+        ) {
+          return undefined;
         }
+
+        return node;
       }
 
       return undefined;
@@ -783,7 +798,7 @@ function componentRule(rule, context) {
     },
 
     isParentComponentNotStatelessComponent(node) {
-      return (
+      return !!(
         node.parent
         && node.parent.key
         && node.parent.key.type === 'Identifier'

tests/lib/rules/no-this-in-sfc.js

@@ -23,7 +23,7 @@ const parserOptions = {
 
 const ruleTester = new RuleTester({parserOptions});
 ruleTester.run('no-this-in-sfc', rule, {
-  valid: [{
+  valid: [].concat({
     code: `
     function Foo(props) {
       const { foo } = props;
@@ -141,7 +141,21 @@ ruleTester.run('no-this-in-sfc', rule, {
         },
       });
     `
-  }],
+  }, {
+    code: `
+      obj.notAComponent = function () {
+        return this.a || null;
+      };`
+  }, parsers.TS([{
+    code: `
+      $.fn.getValueAsStringWeak = function (): string | null {
+        const val = this.length === 1 ? this.val() : null;
+      
+        return typeof val === 'string' ? val : null;
+      };
+    `,
+    parser: parsers['@TYPESCRIPT_ESLINT']
+  }])),
   invalid: [{
     code: `
     function Foo(props) {