fix (#3256)

.changeset/tall-meals-walk.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-mobx": patch
+---
+
+fix `no-anonymous-observer` autofix for arrow functions without BlockStatement body

packages/eslint-plugin-mobx/preview/no-anonymous-observer.js

@@ -1,12 +1,15 @@
 /* eslint mobx/no-anonymous-observer: "error" */
 
-observer(() => { });
-observer(function () { });
-observer(class { });
+observer(() => {})
+observer(function () {})
+observer(class {})
 
-const Cmp = observer(() => { });
-const Cmp = observer(function () { });
-const Cmp = observer(class { });
+const Cmp = observer(() => {})
+const Cmp = observer(() => "") // different autofix
+const Cmp = observer(() => expr()) // different autofix
+const Cmp = observer(() => literal) // different autofix
+const Cmp = observer(function () {})
+const Cmp = observer(class {})
 
-observer(function Name() { });
-observer(class Name { });
+observer(function Name() {})
+observer(class Name {})

packages/eslint-plugin-mobx/src/no-anonymous-observer.js

@@ -1,57 +1,65 @@
-'use strict';
+"use strict"
 
 function create(context) {
-  const sourceCode = context.getSourceCode();
+    const sourceCode = context.getSourceCode()
 
-  return {
-    'CallExpression[callee.name="observer"]': observer => {
-      const cmp = observer.arguments[0];
-      if (!cmp) return;
-      if (cmp?.id?.name) return;
+    return {
+        'CallExpression[callee.name="observer"]': observer => {
+            const cmp = observer.arguments[0]
+            if (!cmp) return
+            if (cmp?.id?.name) return
 
-      const fix = fixer => {
-        // Use name from variable for autofix 
-        const name = observer.parent?.type === 'VariableDeclarator'
-          ? observer.parent.id.name
-          : undefined;
+            const fix = fixer => {
+                // Use name from variable for autofix
+                const name =
+                    observer.parent?.type === "VariableDeclarator"
+                        ? observer.parent.id.name
+                        : undefined
 
-        if (!name) return;
-        if (cmp.type === 'ArrowFunctionExpression') {
-          const arrowToken = sourceCode.getTokenBefore(cmp.body);
-          return [
-            fixer.replaceText(arrowToken, ''),
-            fixer.insertTextBefore(cmp, `function ${name}`),
-          ]
+                if (!name) return
+                if (cmp.type === "ArrowFunctionExpression") {
+                    const arrowToken = sourceCode.getTokenBefore(cmp.body)
+                    const fixes = [
+                        fixer.replaceText(arrowToken, ""),
+                        fixer.insertTextBefore(cmp, `function ${name}`)
+                    ]
+                    if (cmp.body.type !== "BlockStatement") {
+                        fixes.push(
+                            fixer.insertTextBefore(cmp.body, `{ return `),
+                            fixer.insertTextAfter(cmp.body, ` }`)
+                        )
+                    }
+                    return fixes
+                }
+                if (cmp.type === "FunctionExpression") {
+                    const functionToken = sourceCode.getFirstToken(cmp)
+                    return fixer.replaceText(functionToken, `function ${name}`)
+                }
+                if (cmp.type === "ClassExpression") {
+                    const classToken = sourceCode.getFirstToken(cmp)
+                    return fixer.replaceText(classToken, `class ${name}`)
+                }
+            }
+            context.report({
+                node: cmp,
+                messageId: "observerComponentMustHaveName",
+                fix
+            })
         }
-        if (cmp.type === 'FunctionExpression') {
-          const functionToken = sourceCode.getFirstToken(cmp);
-          return fixer.replaceText(functionToken, `function ${name}`);
-        }
-        if (cmp.type === 'ClassExpression') {
-          const classToken = sourceCode.getFirstToken(cmp);
-          return fixer.replaceText(classToken, `class ${name}`);
-        }
-      }
-      context.report({
-        node: cmp,
-        messageId: 'observerComponentMustHaveName',
-        fix,
-      })
-    },
-  };
+    }
 }
 
 module.exports = {
-  meta: {
-    type: 'problem',
-    fixable: 'code',
-    docs: {
-      description: 'forbids anonymous functions or classes as `observer` components',
-      recommended: true,
-    },
-    messages: {
-      observerComponentMustHaveName: "`observer` component must have a name.",
+    meta: {
+        type: "problem",
+        fixable: "code",
+        docs: {
+            description: "forbids anonymous functions or classes as `observer` components",
+            recommended: true
+        },
+        messages: {
+            observerComponentMustHaveName: "`observer` component must have a name."
+        }
     },
-  },
-  create,
-};
+    create
+}