Add dev hint about css object (generated by Babel) being stringified by accident (#1569)

Author: Andarist

.changeset/green-worms-grab.md

@@ -0,0 +1,6 @@
+---
+'babel-plugin-emotion': patch
+'@emotion/babel-preset-css-prop': patch
+---
+
+Add dev hint about css object (generated by Babel) being stringified by accident

packages/babel-plugin-emotion/__tests__/__snapshots__/css-requires-options.js.snap

@@ -16,6 +16,8 @@ const SomeComponent = props => (
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 /** @jsx jsx */
 import { jsx, css } from '@emotion/core';
 
@@ -25,7 +27,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"zszx19-SomeComponent\\",
   styles: \\"color:hotpink;;label:SomeComponent;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImNvcmUtd2l0aC1jc3MtaW1wb3J0LmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQUtZIiwiZmlsZSI6ImNvcmUtd2l0aC1jc3MtaW1wb3J0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3gsIGNzcyB9IGZyb20gJ0BlbW90aW9uL2NvcmUnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBwcm9wcyA9PiAoXG4gIDxkaXZcbiAgICBjc3M9e2Nzc2BcbiAgICAgIGNvbG9yOiBob3RwaW5rO1xuICAgIGB9XG4gICAgey4uLnByb3BzfVxuICAvPlxuKVxuIl19 */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImNvcmUtd2l0aC1jc3MtaW1wb3J0LmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQUtZIiwiZmlsZSI6ImNvcmUtd2l0aC1jc3MtaW1wb3J0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3gsIGNzcyB9IGZyb20gJ0BlbW90aW9uL2NvcmUnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBwcm9wcyA9PiAoXG4gIDxkaXZcbiAgICBjc3M9e2Nzc2BcbiAgICAgIGNvbG9yOiBob3RwaW5rO1xuICAgIGB9XG4gICAgey4uLnByb3BzfVxuICAvPlxuKVxuIl19 */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 const SomeComponent = props => <div css={_ref} {...props} />;"
@@ -65,6 +68,8 @@ function Logo(props) {
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 // @flow
 import * as React from 'react';
 import { jsx } from '@emotion/core';
@@ -75,7 +80,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"1f6ttp4-Logo\\",
   styles: \\"display:block;;label:Logo;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImZ1bmN0aW9uLWRlY2xhcmF0aW9uLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQU9NIiwiZmlsZSI6ImZ1bmN0aW9uLWRlY2xhcmF0aW9uLmpzIiwic291cmNlc0NvbnRlbnQiOlsiLy8gQGZsb3dcbmltcG9ydCAqIGFzIFJlYWN0IGZyb20gJ3JlYWN0J1xuaW1wb3J0IHsganN4IH0gZnJvbSAnQGVtb3Rpb24vY29yZSdcblxuZnVuY3Rpb24gTG9nbyhwcm9wcykge1xuICByZXR1cm4gKFxuICAgIDxhXG4gICAgICBjc3M9e3tcbiAgICAgICAgZGlzcGxheTogJ2Jsb2NrJ1xuICAgICAgfX1cbiAgICAvPlxuICApXG59XG4iXX0= */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImZ1bmN0aW9uLWRlY2xhcmF0aW9uLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQU9NIiwiZmlsZSI6ImZ1bmN0aW9uLWRlY2xhcmF0aW9uLmpzIiwic291cmNlc0NvbnRlbnQiOlsiLy8gQGZsb3dcbmltcG9ydCAqIGFzIFJlYWN0IGZyb20gJ3JlYWN0J1xuaW1wb3J0IHsganN4IH0gZnJvbSAnQGVtb3Rpb24vY29yZSdcblxuZnVuY3Rpb24gTG9nbyhwcm9wcykge1xuICByZXR1cm4gKFxuICAgIDxhXG4gICAgICBjc3M9e3tcbiAgICAgICAgZGlzcGxheTogJ2Jsb2NrJ1xuICAgICAgfX1cbiAgICAvPlxuICApXG59XG4iXX0= */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 function Logo(props) {
@@ -109,6 +115,8 @@ const SomeComponent = props => (
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 /** @jsx jsx */
 import { jsx } from '@emotion/core';
 
@@ -118,7 +126,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"zszx19-SomeComponent\\",
   styles: \\"color:hotpink;;label:SomeComponent;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImpzeC1ob2lzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFLSSIsImZpbGUiOiJqc3gtaG9pc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyIvKiogQGpzeCBqc3ggKi9cbmltcG9ydCB7IGpzeCB9IGZyb20gJ0BlbW90aW9uL2NvcmUnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBwcm9wcyA9PiAoXG4gIDxkaXZcbiAgICBjc3M9e3tcbiAgICAgIGNvbG9yOiAnaG90cGluaydcbiAgICB9fVxuICAgIHsuLi5wcm9wc31cbiAgLz5cbilcbiJdfQ== */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImpzeC1ob2lzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFLSSIsImZpbGUiOiJqc3gtaG9pc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyIvKiogQGpzeCBqc3ggKi9cbmltcG9ydCB7IGpzeCB9IGZyb20gJ0BlbW90aW9uL2NvcmUnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBwcm9wcyA9PiAoXG4gIDxkaXZcbiAgICBjc3M9e3tcbiAgICAgIGNvbG9yOiAnaG90cGluaydcbiAgICB9fVxuICAgIHsuLi5wcm9wc31cbiAgLz5cbilcbiJdfQ== */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 const SomeComponent = props => <div css={_ref} {...props} />;"
@@ -142,6 +151,9 @@ function Logo(props) {
       ↓ ↓ ↓ ↓ ↓ ↓
 
 import _styled from \\"@emotion/styled-base\\";
+
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 // @flow
 import * as React from 'react';
 import { jsx } from '@emotion/core';
@@ -155,7 +167,8 @@ const MyObject = {
   } : {
     name: \\"1lrxbo5\\",
     styles: \\"color:hotpink;\\",
-    map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,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 */\\"
+    map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,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 */\\",
+    toString: _EMOTION_STRINGIFIED_CSS_ERROR__
   })
 };
 
@@ -181,6 +194,8 @@ const SomeComponent = props => (
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 /** @jsx jsx */
 import { jsx } from '@emotion/core';
 
@@ -190,7 +205,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"dwt66v-SomeComponent\\",
   styles: \\"color:hotpink;background-color:green;;label:SomeComponent;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInN0YXRpYy1vYmplY3Qtd2l0aC1jYW1lbC1jYXNlLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQUtJIiwiZmlsZSI6InN0YXRpYy1vYmplY3Qtd2l0aC1jYW1lbC1jYXNlLmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3ggfSBmcm9tICdAZW1vdGlvbi9jb3JlJ1xuXG5jb25zdCBTb21lQ29tcG9uZW50ID0gcHJvcHMgPT4gKFxuICA8ZGl2XG4gICAgY3NzPXt7XG4gICAgICBjb2xvcjogJ2hvdHBpbmsnLFxuICAgICAgYmFja2dyb3VuZENvbG9yOiAnZ3JlZW4nXG4gICAgfX1cbiAgICB7Li4ucHJvcHN9XG4gIC8+XG4pXG4iXX0= */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInN0YXRpYy1vYmplY3Qtd2l0aC1jYW1lbC1jYXNlLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQUtJIiwiZmlsZSI6InN0YXRpYy1vYmplY3Qtd2l0aC1jYW1lbC1jYXNlLmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3ggfSBmcm9tICdAZW1vdGlvbi9jb3JlJ1xuXG5jb25zdCBTb21lQ29tcG9uZW50ID0gcHJvcHMgPT4gKFxuICA8ZGl2XG4gICAgY3NzPXt7XG4gICAgICBjb2xvcjogJ2hvdHBpbmsnLFxuICAgICAgYmFja2dyb3VuZENvbG9yOiAnZ3JlZW4nXG4gICAgfX1cbiAgICB7Li4ucHJvcHN9XG4gIC8+XG4pXG4iXX0= */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 const SomeComponent = props => <div css={_ref} {...props} />;"
@@ -218,6 +234,8 @@ const SomeComponent = props => {
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 /** @jsx jsx */
 import { jsx } from '@emotion/core';
 
@@ -227,7 +245,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"1vvht02-SomeComponent\\",
   styles: \\"color:green;:hover{color:hotpink;};label:SomeComponent;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,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 */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,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 */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 const SomeComponent = props => {

packages/babel-plugin-emotion/__tests__/__snapshots__/css.js.snap

@@ -9,13 +9,17 @@ css({ color: 'hotpink' })
       ↓ ↓ ↓ ↓ ↓ ↓
 
 import _css from \\"@emotion/css\\";
+
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 process.env.NODE_ENV === \\"production\\" ? {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\"
 } : {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFQSIsImZpbGUiOiJzb3VyY2UtbWFwLnRlc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyJpbXBvcnQgY3NzIGZyb20gJ0BlbW90aW9uL2NzcydcblxuY3NzKHsgY29sb3I6ICdob3RwaW5rJyB9KVxuIl19 */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFQSIsImZpbGUiOiJzb3VyY2UtbWFwLnRlc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyJpbXBvcnQgY3NzIGZyb20gJ0BlbW90aW9uL2NzcydcblxuY3NzKHsgY29sb3I6ICdob3RwaW5rJyB9KVxuIl19 */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };"
 `;
 
@@ -28,6 +32,8 @@ const SomeComponent = props => <div css={{ color: 'hotpink' }} {...props} />
 
       ↓ ↓ ↓ ↓ ↓ ↓
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 /** @jsx jsx */
 import { jsx } from '@emotion/core';
 
@@ -37,7 +43,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"zszx19-SomeComponent\\",
   styles: \\"color:hotpink;;label:SomeComponent;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFHb0MiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3ggfSBmcm9tICdAZW1vdGlvbi9jb3JlJ1xuXG5jb25zdCBTb21lQ29tcG9uZW50ID0gcHJvcHMgPT4gPGRpdiBjc3M9e3sgY29sb3I6ICdob3RwaW5rJyB9fSB7Li4ucHJvcHN9IC8+XG4iXX0= */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFHb0MiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiLyoqIEBqc3gganN4ICovXG5pbXBvcnQgeyBqc3ggfSBmcm9tICdAZW1vdGlvbi9jb3JlJ1xuXG5jb25zdCBTb21lQ29tcG9uZW50ID0gcHJvcHMgPT4gPGRpdiBjc3M9e3sgY29sb3I6ICdob3RwaW5rJyB9fSB7Li4ucHJvcHN9IC8+XG4iXX0= */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 const SomeComponent = props => <div css={_ref} {...props} />;"
@@ -82,13 +89,17 @@ css\`
       ↓ ↓ ↓ ↓ ↓ ↓
 
 import _css from \\"@emotion/css\\";
+
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 process.env.NODE_ENV === \\"production\\" ? {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\"
 } : {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFRyIsImZpbGUiOiJzb3VyY2UtbWFwLnRlc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyJpbXBvcnQgY3NzIGZyb20gJ0BlbW90aW9uL2NzcydcblxuY3NzYFxuICBjb2xvcjogaG90cGluaztcbmBcbiJdfQ== */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFRyIsImZpbGUiOiJzb3VyY2UtbWFwLnRlc3QuanMiLCJzb3VyY2VzQ29udGVudCI6WyJpbXBvcnQgY3NzIGZyb20gJ0BlbW90aW9uL2NzcydcblxuY3NzYFxuICBjb2xvcjogaG90cGluaztcbmBcbiJdfQ== */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };"
 `;
 
@@ -130,6 +141,8 @@ const SomeComponent = styled.div({
 
 import _styled from \\"@emotion/styled-base\\";
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 const SomeComponent = _styled(\\"div\\", {
   target: \\"eb28ebz0\\",
   label: \\"SomeComponent\\"
@@ -139,7 +152,8 @@ const SomeComponent = _styled(\\"div\\", {
 } : {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFc0IiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0IHN0eWxlZCBmcm9tICdAZW1vdGlvbi9zdHlsZWQnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBzdHlsZWQuZGl2KHtcbiAgY29sb3I6ICdob3RwaW5rJ1xufSlcbiJdfQ== */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFc0IiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0IHN0eWxlZCBmcm9tICdAZW1vdGlvbi9zdHlsZWQnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBzdHlsZWQuZGl2KHtcbiAgY29sb3I6ICdob3RwaW5rJ1xufSlcbiJdfQ== */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 });"
 `;
 
@@ -155,6 +169,8 @@ const SomeComponent = styled.div\`
 
 import _styled from \\"@emotion/styled-base\\";
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 const SomeComponent = _styled(\\"div\\", {
   target: \\"eb28ebz0\\",
   label: \\"SomeComponent\\"
@@ -164,6 +180,7 @@ const SomeComponent = _styled(\\"div\\", {
 } : {
   name: \\"1lrxbo5\\",
   styles: \\"color:hotpink;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFZ0MiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0IHN0eWxlZCBmcm9tICdAZW1vdGlvbi9zdHlsZWQnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBzdHlsZWQuZGl2YFxuICBjb2xvcjogaG90cGluaztcbmBcbiJdfQ== */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXAudGVzdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFZ0MiLCJmaWxlIjoic291cmNlLW1hcC50ZXN0LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0IHN0eWxlZCBmcm9tICdAZW1vdGlvbi9zdHlsZWQnXG5cbmNvbnN0IFNvbWVDb21wb25lbnQgPSBzdHlsZWQuZGl2YFxuICBjb2xvcjogaG90cGluaztcbmBcbiJdfQ== */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 });"
 `;

packages/babel-plugin-emotion/__tests__/__snapshots__/index.js.snap

@@ -8,6 +8,13 @@ import { simplifyObject } from './object-to-string'
 import { appendStringToArguments, joinStringLiterals } from './strings'
 import { isTaggedTemplateExpressionTranspiledByTypeScript } from './checks'
 
+const CSS_OBJECT_STRINGIFIED_ERROR =
+  "You have tried to stringify object returned from `css` function. It isn't supposed to be used directly (e.g. as value of the `className` prop), but rather handed to emotion so it can handle it (e.g. as value of `css` prop)."
+
+// with babel@6 fallback
+const cloneNode = (t, node) =>
+  typeof t.cloneNode === 'function' ? t.cloneNode(node) : t.cloneDeep(node)
+
 function createSourceMapConditional(t, production, development) {
   return t.conditionalExpression(
     t.binaryExpression(
@@ -91,10 +98,29 @@ export let transformExpressionWithStyles = ({
       ])
       let node = prodNode
       if (sourceMap) {
+        if (!state.emotionStringifiedCssId) {
+          const uid = state.file.scope.generateUidIdentifier(
+            '__EMOTION_STRINGIFIED_CSS_ERROR__'
+          )
+          state.emotionStringifiedCssId = uid
+          const cssObjectToString = t.functionDeclaration(
+            uid,
+            [],
+            t.blockStatement([
+              t.returnStatement(t.stringLiteral(CSS_OBJECT_STRINGIFIED_ERROR))
+            ])
+          )
+          cssObjectToString._compact = true
+          state.file.path.unshiftContainer('body', [cssObjectToString])
+        }
         let devNode = t.objectExpression([
           t.objectProperty(t.identifier('name'), t.stringLiteral(res.name)),
           t.objectProperty(t.identifier('styles'), t.stringLiteral(res.styles)),
-          t.objectProperty(t.identifier('map'), t.stringLiteral(sourceMap))
+          t.objectProperty(t.identifier('map'), t.stringLiteral(sourceMap)),
+          t.objectProperty(
+            t.identifier('toString'),
+            cloneNode(t, state.emotionStringifiedCssId)
+          )
         ])
         node = createSourceMapConditional(t, prodNode, devNode)
       }
@@ -128,7 +154,7 @@ export let transformExpressionWithStyles = ({
             t.binaryExpression(
               '+',
               lastElement.node,
-              t.cloneNode(sourceMapConditional)
+              cloneNode(t, sourceMapConditional)
             )
           )
         })

packages/babel-plugin-emotion/__tests__/__snapshots__/styled.js.snap

@@ -23,6 +23,8 @@ import { jsx as ___EmotionJSX } from \\"@emotion/core\\";
 
 function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
 
+function _EMOTION_STRINGIFIED_CSS_ERROR__() { return \\"You have tried to stringify object returned from \`css\` function. It isn't supposed to be used directly (e.g. as value of the \`className\` prop), but rather handed to emotion so it can handle it (e.g. as value of \`css\` prop).\\"; }
+
 import * as React from 'react';
 
 var _ref = process.env.NODE_ENV === \\"production\\" ? {
@@ -31,7 +33,8 @@ var _ref = process.env.NODE_ENV === \\"production\\" ? {
 } : {
   name: \\"1q24rv0-Button\\",
   styles: \\"color:hotpink;;label:Button;\\",
-  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImluZGV4LmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQU1RIiwiZmlsZSI6ImluZGV4LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0ICogYXMgUmVhY3QgZnJvbSAncmVhY3QnXG5cbmV4cG9ydCBsZXQgQnV0dG9uID0gcHJvcHMgPT4ge1xuICByZXR1cm4gKFxuICAgIDw+XG4gICAgICA8YnV0dG9uXG4gICAgICAgIGNzcz17e1xuICAgICAgICAgIGNvbG9yOiAnaG90cGluaydcbiAgICAgICAgfX1cbiAgICAgICAgey4uLnByb3BzfVxuICAgICAgLz5cbiAgICA8Lz5cbiAgKVxufVxuIl19 */\\"
+  map: \\"/*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImluZGV4LmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQU1RIiwiZmlsZSI6ImluZGV4LmpzIiwic291cmNlc0NvbnRlbnQiOlsiaW1wb3J0ICogYXMgUmVhY3QgZnJvbSAncmVhY3QnXG5cbmV4cG9ydCBsZXQgQnV0dG9uID0gcHJvcHMgPT4ge1xuICByZXR1cm4gKFxuICAgIDw+XG4gICAgICA8YnV0dG9uXG4gICAgICAgIGNzcz17e1xuICAgICAgICAgIGNvbG9yOiAnaG90cGluaydcbiAgICAgICAgfX1cbiAgICAgICAgey4uLnByb3BzfVxuICAgICAgLz5cbiAgICA8Lz5cbiAgKVxufVxuIl19 */\\",
+  toString: _EMOTION_STRINGIFIED_CSS_ERROR__
 };
 
 export let Button = props => {