[Fix] Bring experimental_sx back with error code

docs/public/static/error-codes.json

@@ -17,5 +17,6 @@
   "16": "MUI: withTheme is no longer exported from @mui/material/styles.\nYou have to import it from @mui/styles.\nSee https://mui.com/r/migration-v4/#mui-material-styles for more details.",
   "17": "MUI: Expected valid input target. Did you use a custom `slots.input` and forget to forward refs? See https://mui.com/r/input-component-ref-interface for more info.",
   "18": "MUI: `vars` is a private field used for CSS variables support.\nPlease use another name.",
-  "19": "MUI: `useColorScheme` must be called under <CssVarsProvider />"
+  "19": "MUI: `useColorScheme` must be called under <CssVarsProvider />",
+  "20": "MUI: The `experimental_sx` has been moved to `theme.unstable_sx`.For more details, see https://github.com/mui/material-ui/pull/35150."
 }

packages/mui-material/src/styles/index.d.ts

@@ -65,6 +65,9 @@ export {
   StyledEngineProvider,
   SxProps,
 } from '@mui/system';
+// TODO: Remove this function in v6.
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function experimental_sx(): any;
 export { default as useTheme } from './useTheme';
 export { default as useThemeProps } from './useThemeProps';
 export * from './useThemeProps';

packages/mui-material/src/styles/index.js

@@ -1,3 +1,5 @@
+import MuiError from '@mui/utils/macros/MuiError.macro';
+
 export { default as adaptV4Theme } from './adaptV4Theme';
 export {
   hexToRgb,
@@ -14,6 +16,14 @@ export {
   css,
   keyframes,
 } from '@mui/system';
+// TODO: Remove this function in v6.
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function experimental_sx() {
+  throw new MuiError(
+    'MUI: The `experimental_sx` has been moved to `theme.unstable_sx`.' +
+      'For more details, see https://github.com/mui/material-ui/pull/35150.',
+  );
+}
 export { default as createTheme, createMuiTheme } from './createTheme';
 export { default as unstable_createMuiStrictModeTheme } from './createMuiStrictModeTheme';
 export { default as createStyles } from './createStyles';

packages/mui-system/src/index.d.ts

@@ -123,6 +123,10 @@ export {
 } from './styleFunctionSx';
 export * from './styleFunctionSx';
 
+// TODO: Remove this function in v6.
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function experimental_sx(): any;
+
 export { default as Box } from './Box';
 export * from './Box';
 

packages/mui-system/src/index.js

@@ -1,3 +1,5 @@
+import MuiError from '@mui/utils/macros/MuiError.macro';
+
 export { css, keyframes, GlobalStyles, StyledEngineProvider } from '@mui/styled-engine';
 export { default as borders } from './borders';
 export * from './borders';
@@ -31,6 +33,14 @@ export {
   extendSxProp as unstable_extendSxProp,
   unstable_defaultSxConfig,
 } from './styleFunctionSx';
+// TODO: Remove this function in v6
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function experimental_sx() {
+  throw new MuiError(
+    'MUI: The `experimental_sx` has been moved to `theme.unstable_sx`.' +
+      'For more details, see https://github.com/mui/material-ui/pull/35150.',
+  );
+}
 export { default as unstable_getThemeValue } from './getThemeValue';
 export { default as Box } from './Box';
 export { default as createBox } from './createBox';