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feat(rules): add no-complex-expressions-in-message rule
Disallows complex expressions (binary ops, function calls, conditionals) in Lingui messages. Configurable via: - allowedCallees: whitelist function names (default: i18n helpers) - allowMemberExpressions: allow props.name style access - maxExpressionDepth: limit member chain depth
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‎README.md‎

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| Rule | Description | Recommended |
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|------|-------------|:-----------:|
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| [no-complex-expressions-in-message](docs/rules/no-complex-expressions-in-message.md) | Restrict complexity of expressions in messages | ✅ |
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| [no-nested-macros](docs/rules/no-nested-macros.md) | Disallow nesting Lingui macros | ✅ |
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| [no-single-tag-message](docs/rules/no-single-tag-message.md) | Disallow messages with only a single markup tag | ✅ |
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| [no-single-variable-message](docs/rules/no-single-variable-message.md) | Disallow messages that consist only of a single variable | ✅ |
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### Planned Rules
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- `no-complex-expressions-in-message` — Restrict complexity of expressions in messages
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- `valid-t-call-location` — Enforce valid locations for `t` macro calls
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- `no-unlocalized-strings` — Detect user-visible strings not wrapped in Lingui
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- `text-restrictions` — Enforce project-specific text restrictions

‎docs/rules/no-complex-expressions-in-message.md‎

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# no-complex-expressions-in-message
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Disallow complex expressions in Lingui messages.
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## Why?
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Complex expressions in translation messages:
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- Make it harder for translators to understand the context
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- Can cause issues with message extraction
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- May lead to runtime errors if the expression fails
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- Make the code harder to maintain
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Extract complex logic to variables before using them in messages.
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## Rule Details
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This rule reports complex expressions inside `t` tagged templates and `<Trans>` components.
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### ❌ Invalid
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```tsx
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// Binary/arithmetic expressions
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t`Price: ${price * 1.2}`
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<Trans>Total: {count + 1}</Trans>
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// Non-whitelisted function calls
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t`Random: ${Math.random()}`
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<Trans>Date: {formatDate(date)}</Trans>
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t`Items: ${items.join(', ')}`
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// Member expressions (by default)
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t`Hello ${user.name}`
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// Conditional expressions
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t`Status: ${isActive ? 'Active' : 'Inactive'}`
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// Logical expressions
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t`Name: ${name || 'Unknown'}`
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```
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### ✅ Valid
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```tsx
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// Simple identifiers
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t`Hello ${name}`
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<Trans>You have {count} items</Trans>
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// Whitelisted Lingui helpers
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t`Price: ${i18n.number(price)}`
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t`Date: ${i18n.date(date)}`
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<Trans>Items: {i18n.plural(count, { one: '#', other: '#' })}</Trans>
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// Extract complex logic first
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const displayPrice = price * 1.2
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t`Price: ${displayPrice}`
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const formattedDate = formatDate(date)
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<Trans>Date: {formattedDate}</Trans>
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```
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## Options
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### `allowedCallees`
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Array of function names that are allowed. Format: dot-separated strings.
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Default: `["i18n.number", "i18n.date", "i18n.plural", "i18n.select"]`
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```ts
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{
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"lingui-ts/no-complex-expressions-in-message": ["error", {
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"allowedCallees": ["i18n.number", "i18n.date", "formatCurrency"]
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}]
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}
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```
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### `allowMemberExpressions`
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Whether to allow simple member expressions like `props.name`. Default: `false`
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```ts
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{
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"lingui-ts/no-complex-expressions-in-message": ["error", {
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"allowMemberExpressions": true
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}]
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}
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```
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### `maxExpressionDepth`
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Maximum depth for member expression chains when `allowMemberExpressions` is `true`. Default: `1`
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- `1`: allows `user.name` but not `user.address.street`
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- `2`: allows up to `user.address.street`
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- `null`: no limit
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```ts
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{
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"lingui-ts/no-complex-expressions-in-message": ["error", {
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"allowMemberExpressions": true,
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"maxExpressionDepth": 2
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}]
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}
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```
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## When Not To Use It
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If your codebase has established patterns that rely on inline expressions and you handle translation complexity elsewhere, you can disable this rule.
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‎src/index.ts‎

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* @packageDocumentation
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*/
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import { noComplexExpressionsInMessage } from "./rules/no-complex-expressions-in-message.js"
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import { noNestedMacros } from "./rules/no-nested-macros.js"
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import { noSingleTagMessage } from "./rules/no-single-tag-message.js"
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import { noSingleVariableMessage } from "./rules/no-single-variable-message.js"
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version: "1.0.0"
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},
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rules: {
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"no-complex-expressions-in-message": noComplexExpressionsInMessage,
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"no-nested-macros": noNestedMacros,
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"no-single-tag-message": noSingleTagMessage,
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"no-single-variable-message": noSingleVariableMessage
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"lingui-ts": plugin
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},
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rules: {
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"lingui-ts/no-complex-expressions-in-message": "error",
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"lingui-ts/no-nested-macros": "error",
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"lingui-ts/no-single-tag-message": "error",
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"lingui-ts/no-single-variable-message": "error"

‎src/rules/no-complex-expressions-in-message.test.ts‎

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import { RuleTester } from "@typescript-eslint/rule-tester"
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import { afterAll, describe, it } from "vitest"
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import { noComplexExpressionsInMessage } from "./no-complex-expressions-in-message.js"
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RuleTester.afterAll = afterAll
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RuleTester.describe = describe
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RuleTester.it = it
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const ruleTester = new RuleTester({
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languageOptions: {
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parserOptions: {
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ecmaVersion: 2022,
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sourceType: "module",
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ecmaFeatures: {
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jsx: true
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}
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}
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}
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})
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ruleTester.run("no-complex-expressions-in-message", noComplexExpressionsInMessage, {
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valid: [
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// Simple identifiers in t``
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"t`Hello ${name}`",
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"t`You have ${count} items`",
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"t`${greeting}, ${name}!`",
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// Simple identifiers in <Trans>
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"<Trans>Hello {name}</Trans>",
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"<Trans>You have {count} items</Trans>",
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// Allowed callees (default: i18n.number, i18n.date, etc.)
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"t`Price: ${i18n.number(price)}`",
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"t`Date: ${i18n.date(date)}`",
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"<Trans>Price: {i18n.number(price)}</Trans>",
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"<Trans>Items: {i18n.plural(count, { one: '#', other: '#' })}</Trans>",
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// Member expressions when allowed
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{
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code: "t`Hello ${props.name}`",
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options: [{ allowMemberExpressions: true, allowedCallees: [], maxExpressionDepth: 1 }]
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},
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{
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code: "<Trans>Hello {user.name}</Trans>",
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options: [{ allowMemberExpressions: true, allowedCallees: [], maxExpressionDepth: 1 }]
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},
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// Non-Lingui tagged templates should be ignored
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"css`color: ${theme.primary}`",
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"html`<div>${content}</div>`",
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// Non-Trans JSX elements should be ignored
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"<div>{Math.random()}</div>",
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"<Plural>{count * 2}</Plural>"
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],
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invalid: [
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// Binary expressions
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{
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code: "t`Price: ${price * 1.2}`",
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errors: [{ messageId: "complexExpression" }]
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},
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{
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code: "<Trans>Total: {count + 1}</Trans>",
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errors: [{ messageId: "complexExpression" }]
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},
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// Non-whitelisted function calls
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{
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code: "t`Random: ${Math.random()}`",
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errors: [{ messageId: "complexExpression" }]
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},
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{
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code: "<Trans>Date: {formatDate(date)}</Trans>",
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errors: [{ messageId: "complexExpression" }]
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},
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{
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code: "t`Items: ${items.join(', ')}`",
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errors: [{ messageId: "complexExpression" }]
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},
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// Member expressions when not allowed (default)
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{
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code: "t`Hello ${user.name}`",
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errors: [{ messageId: "complexExpression" }]
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},
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{
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code: "<Trans>Hello {props.value}</Trans>",
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errors: [{ messageId: "complexExpression" }]
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},
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// Deep member expressions even when allowed
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{
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code: "t`Street: ${user.address.street}`",
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options: [{ allowMemberExpressions: true, allowedCallees: [], maxExpressionDepth: 1 }],
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errors: [{ messageId: "complexExpression" }]
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},
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// Optional chaining
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{
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code: "t`Name: ${user?.name}`",
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options: [{ allowMemberExpressions: true, allowedCallees: [], maxExpressionDepth: 1 }],
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errors: [{ messageId: "complexExpression" }]
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},
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// Conditional expressions
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{
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code: "t`Status: ${isActive ? 'Active' : 'Inactive'}`",
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errors: [{ messageId: "complexExpression" }]
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},
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{
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code: "<Trans>Status: {isActive ? 'on' : 'off'}</Trans>",
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errors: [{ messageId: "complexExpression" }]
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},
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// Logical expressions
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{
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code: "t`Name: ${name || 'Unknown'}`",
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errors: [{ messageId: "complexExpression" }]
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},
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// Template literals inside
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{
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code: "t`Value: ${`nested ${x}`}`",
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errors: [{ messageId: "complexExpression" }]
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},
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// Multiple violations in one message
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{
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code: "t`${a + b} and ${Math.random()}`",
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errors: [
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{ messageId: "complexExpression" },
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{ messageId: "complexExpression" }
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]
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},
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{
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code: "<Trans>{x * 2} plus {y * 3}</Trans>",
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errors: [
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{ messageId: "complexExpression" },
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{ messageId: "complexExpression" }
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]
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}
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]
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})
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