Add --check option (#5629)

docs/api.md

@@ -18,7 +18,7 @@ prettier.format("foo ( );", { semi: false, parser: "babylon" });
 
 ## `prettier.check(source [, options])`
 
-`check` checks to see if the file has been formatted with Prettier given those options and returns a `Boolean`. This is similar to the `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios.
+`check` checks to see if the file has been formatted with Prettier given those options and returns a `Boolean`. This is similar to the `--check` or `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios.
 
 ## `prettier.formatWithCursor(source [, options])`
 

docs/cli.md

@@ -21,6 +21,38 @@ Don't forget the quotes around the globs! The quotes make sure that Prettier exp
 
 Prettier CLI will ignore files located in `node_modules` directory. To opt-out from this behavior use `--with-node-modules` flag.
 
+## `--check`
+
+When you want to check if your files are formatted, you can run Prettier with the `--check` flag (or `-c`).
+This will output a human-friendly message and a list of unformatted files, if any.
+
+```bash
+prettier --check "src/**/*.js"
+```
+
+Console output if all files are formatted:
+
+```
+Checking formatting...
+All matched files use Prettier code style!
+```
+
+Console output if some of the files require re-formatting:
+
+```
+Checking formatting...
+src/fileA.js
+src/fileB.js
+Code style issues found in the above file(s). Forgot to run Prettier?
+```
+
+The command will return exit code 1 in the second case, which is helpful inside the CI pipelines.
+Human-friendly status messages help project contributors react on possible problems.
+To minimise the number of times `prettier --check` finds unformatted files, you may be interested in configuring a [pre-commit hook](precommit.md) in your repo.
+Applying this practice will minimise the number of times the CI fails because of code formatting problems.
+
+If you need to pipe the list of unformatted files to another command, you can use [`--list-different`](./cli.md#list-different) flag instead of `--check`.
+
 ## `--debug-check`
 
 If you're worried that Prettier will change the correctness of your code, add `--debug-check` to the command. This will cause Prettier to print an error message if it detects that code correctness might have changed. Note that `--write` cannot be used with `--debug-check`.
@@ -72,6 +104,8 @@ Another useful flag is `--list-different` (or `-l`) which prints the filenames o
 prettier --single-quote --list-different "src/**/*.js"
 ```
 
+You can also use [`--check`](./cli.md#check) flag, which works the same way as `--list-different`, but also prints a human-friendly summary message to stdout.
+
 ## `--no-config`
 
 Do not look for a configuration file. The default settings will be used.

docs/options.md

@@ -310,7 +310,7 @@ If you want to make sure that your git repository only contains Linux-style line
 
 1. Set `endOfLine` option to `lf`
 1. Configure [a pre-commit hook](./precommit.md) that will run Prettier
-1. Configure Prettier to run in your CI pipeline (e.g. using [`prettier-check` npm package](https://www.npmjs.com/package/prettier-check))
+1. Configure Prettier to run in your CI pipeline using [`--check` flag](./cli.md#check)
 1. Ask Windows users to run `git config core.autocrlf false` before working on your repo so that git did not convert `LF` to `CRLF` on checkout.
    Alternatively, you can add `* text=auto eol=lf` to the repo's `.gitattributes` file to achieve this.
 

src/cli/constant.js

@@ -70,6 +70,15 @@ const categoryOrder = [
  * Note: The options below are sorted alphabetically.
  */
 const options = {
+  check: {
+    type: "boolean",
+    category: coreOptions.CATEGORY_OUTPUT,
+    alias: "c",
+    description: dedent`
+      Check if the given files are formatted, print a human-friendly summary
+      message and paths to unformatted files (see also --list-different).
+    `
+  },
   color: {
     // The supports-color package (a sub sub dependency) looks directly at
     // `process.argv` for `--no-color` and such-like options. The reason it is
@@ -170,7 +179,7 @@ const options = {
     category: coreOptions.CATEGORY_OUTPUT,
     alias: "l",
     description:
-      "Print the names of files that are different from Prettier's formatting."
+      "Print the names of files that are different from Prettier's formatting (see also --check)."
   },
   loglevel: {
     type: "choice",

src/cli/index.js

@@ -12,6 +12,11 @@ function run(args) {
 
     context.logger.debug(`normalized argv: ${JSON.stringify(context.argv)}`);
 
+    if (context.argv["check"] && context.argv["list-different"]) {
+      context.logger.error("Cannot use --check and --list-different together.");
+      process.exit(1);
+    }
+
     if (context.argv["write"] && context.argv["debug-check"]) {
       context.logger.error("Cannot use --write and --debug-check together.");
       process.exit(1);

src/cli/util.js

@@ -58,7 +58,7 @@ function handleError(context, filename, error) {
       readline.clearLine(process.stdout, 0);
       readline.cursorTo(process.stdout, 0, null);
     }
-    if (!context.argv["list-different"]) {
+    if (!context.argv["check"] && !context.argv["list-different"]) {
       process.exitCode = 2;
     }
     context.logger.error(error.message);
@@ -133,7 +133,7 @@ function writeOutput(context, result, options) {
 }
 
 function listDifferent(context, input, options, filename) {
-  if (!context.argv["list-different"]) {
+  if (!context.argv["check"] && !context.argv["list-different"]) {
     return;
   }
 
@@ -441,18 +441,25 @@ function formatFiles(context) {
   // before any files are actually written
   const ignorer = createIgnorerFromContextOrDie(context);
 
+  let numberOfUnformattedFilesFound = 0;
+
+  if (context.argv["check"]) {
+    context.logger.log("Checking formatting...");
+  }
+
   eachFilename(context, context.filePatterns, (filename, options) => {
     const fileIgnored = ignorer.filter([filename]).length === 0;
     if (
       fileIgnored &&
       (context.argv["debug-check"] ||
         context.argv["write"] ||
+        context.argv["check"] ||
         context.argv["list-different"])
     ) {
       return;
     }
 
-    if (context.argv["write"] && process.stdout.isTTY) {
+    if (process.stdout.isTTY) {
       // Don't use `console.log` here since we need to replace this line.
       context.logger.log(filename, { newline: false });
     }
@@ -496,24 +503,17 @@ function formatFiles(context) {
 
     const isDifferent = output !== input;
 
-    if (context.argv["list-different"] && isDifferent) {
-      context.logger.log(filename);
-      if (!context.argv["write"]) {
-        process.exitCode = 1;
-      }
+    if (process.stdout.isTTY) {
+      // Remove previously printed filename to log it with duration.
+      readline.clearLine(process.stdout, 0);
+      readline.cursorTo(process.stdout, 0, null);
     }
 
     if (context.argv["write"]) {
-      if (process.stdout.isTTY) {
-        // Remove previously printed filename to log it with duration.
-        readline.clearLine(process.stdout, 0);
-        readline.cursorTo(process.stdout, 0, null);
-      }
-
       // Don't write the file if it won't change in order not to invalidate
       // mtime based caches.
       if (isDifferent) {
-        if (!context.argv["list-different"]) {
+        if (!context.argv["check"] && !context.argv["list-different"]) {
           context.logger.log(`${filename} ${Date.now() - start}ms`);
         }
 
@@ -526,7 +526,7 @@ function formatFiles(context) {
           // Don't exit the process if one file failed
           process.exitCode = 2;
         }
-      } else if (!context.argv["list-different"]) {
+      } else if (!context.argv["check"] && !context.argv["list-different"]) {
         context.logger.log(`${chalk.grey(filename)} ${Date.now() - start}ms`);
       }
     } else if (context.argv["debug-check"]) {
@@ -535,10 +535,39 @@ function formatFiles(context) {
       } else {
         process.exitCode = 2;
       }
-    } else if (!context.argv["list-different"]) {
+    } else if (!context.argv["check"] && !context.argv["list-different"]) {
       writeOutput(context, result, options);
     }
+
+    if (
+      (context.argv["check"] || context.argv["list-different"]) &&
+      isDifferent
+    ) {
+      context.logger.log(filename);
+      numberOfUnformattedFilesFound += 1;
+    }
   });
+
+  // Print check summary based on expected exit code
+  if (context.argv["check"]) {
+    context.logger.log(
+      numberOfUnformattedFilesFound === 0
+        ? "All matched files use Prettier code style!"
+        : context.argv["write"]
+        ? "Code style issues fixed in the above file(s)."
+        : "Code style issues found in the above file(s). Forgot to run Prettier?"
+    );
+  }
+
+  // Ensure non-zero exitCode when using --check/list-different is not combined with --write
+  if (
+    (context.argv["check"] || context.argv["list-different"]) &&
+    numberOfUnformattedFilesFound > 0 &&
+    !process.exitCode &&
+    !context.argv["write"]
+  ) {
+    process.exitCode = 1;
+  }
 }
 
 function getOptionsWithOpposites(options) {

tests_integration/__tests__/__snapshots__/check.js.snap

@@ -0,0 +1,5 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`checks stdin with --check (write) 1`] = `Array []`;
+
+exports[`checks stdin with -c (alias for --check) (write) 1`] = `Array []`;

tests_integration/__tests__/__snapshots__/debug-check.js.snap

@@ -4,6 +4,17 @@ exports[`checks stdin with --debug-check (write) 1`] = `Array []`;
 
 exports[`doesn't crash when --debug-check is passed (write) 1`] = `Array []`;
 
+exports[`should not exit non-zero for already prettified code with --debug-check + --check (stderr) 1`] = `""`;
+
+exports[`should not exit non-zero for already prettified code with --debug-check + --check (stdout) 1`] = `
+"Checking formatting...
+issue-4599.js
+All matched files use Prettier code style!
+"
+`;
+
+exports[`should not exit non-zero for already prettified code with --debug-check + --check (write) 1`] = `Array []`;
+
 exports[`should not exit non-zero for already prettified code with --debug-check + --list-different (stderr) 1`] = `""`;
 
 exports[`should not exit non-zero for already prettified code with --debug-check + --list-different (stdout) 1`] = `

tests_integration/__tests__/__snapshots__/early-exit.js.snap

@@ -5,7 +5,7 @@ exports[`show detailed usage with --help l (alias) (stderr) 1`] = `""`;
 exports[`show detailed usage with --help l (alias) (stdout) 1`] = `
 "-l, --list-different
 
-  Print the names of files that are different from Prettier's formatting.
+  Print the names of files that are different from Prettier's formatting (see also --check).
 "
 `;
 
@@ -51,7 +51,9 @@ Stdin is read if it is piped to Prettier and no files are given.
 
 Output options:
 
-  -l, --list-different     Print the names of files that are different from Prettier's formatting.
+  -c, --check              Check if the given files are formatted, print a human-friendly summary
+                           message and paths to unformatted files (see also --list-different).
+  -l, --list-different     Print the names of files that are different from Prettier's formatting (see also --check).
   --write                  Edit files in-place. (Beware!)
 
 Format options:
@@ -197,7 +199,9 @@ Stdin is read if it is piped to Prettier and no files are given.
 
 Output options:
 
-  -l, --list-different     Print the names of files that are different from Prettier's formatting.
+  -c, --check              Check if the given files are formatted, print a human-friendly summary
+                           message and paths to unformatted files (see also --list-different).
+  -l, --list-different     Print the names of files that are different from Prettier's formatting (see also --check).
   --write                  Edit files in-place. (Beware!)
 
 Format options:
@@ -296,6 +300,15 @@ Other options:
 
 exports[`throw error and show usage with something unexpected (write) 1`] = `Array []`;
 
+exports[`throw error with --check + --list-different (stderr) 1`] = `
+"[error] Cannot use --check and --list-different together.
+"
+`;
+
+exports[`throw error with --check + --list-different (stdout) 1`] = `""`;
+
+exports[`throw error with --check + --list-different (write) 1`] = `Array []`;
+
 exports[`throw error with --file-info + multiple files (stderr) 1`] = `
 "[error] Cannot use --file-info with multiple files
 "

tests_integration/__tests__/__snapshots__/help-options.js.snap

@@ -31,6 +31,18 @@ Default: true
 
 exports[`show detailed usage with --help bracket-spacing (write) 1`] = `Array []`;
 
+exports[`show detailed usage with --help check (stderr) 1`] = `""`;
+
+exports[`show detailed usage with --help check (stdout) 1`] = `
+"-c, --check
+
+  Check if the given files are formatted, print a human-friendly summary
+  message and paths to unformatted files (see also --list-different).
+"
+`;
+
+exports[`show detailed usage with --help check (write) 1`] = `Array []`;
+
 exports[`show detailed usage with --help color (stderr) 1`] = `""`;
 
 exports[`show detailed usage with --help color (stdout) 1`] = `
@@ -235,7 +247,7 @@ exports[`show detailed usage with --help list-different (stderr) 1`] = `""`;
 exports[`show detailed usage with --help list-different (stdout) 1`] = `
 "-l, --list-different
 
-  Print the names of files that are different from Prettier's formatting.
+  Print the names of files that are different from Prettier's formatting (see also --check).
 "
 `;
 

tests_integration/__tests__/__snapshots__/infer-parser.js.snap

@@ -1,5 +1,28 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`--check with unknown path and no parser multiple files (stderr) 1`] = `
+"[error] No parser could be inferred for file: FOO
+"
+`;
+
+exports[`--check with unknown path and no parser multiple files (stdout) 1`] = `
+"Checking formatting...
+foo.js
+Code style issues found in the above file(s). Forgot to run Prettier?
+"
+`;
+
+exports[`--check with unknown path and no parser specific file (stderr) 1`] = `
+"[error] No parser could be inferred for file: FOO
+"
+`;
+
+exports[`--check with unknown path and no parser specific file (stdout) 1`] = `
+"Checking formatting...
+All matched files use Prettier code style!
+"
+`;
+
 exports[`--list-different with unknown path and no parser multiple files (stderr) 1`] = `
 "[error] No parser could be inferred for file: FOO
 "
@@ -10,6 +33,39 @@ exports[`--list-different with unknown path and no parser specific file (stderr)
 "
 `;
 
+exports[`--write and --check with unknown path and no parser multiple files (stderr) 1`] = `
+"[error] No parser could be inferred for file: FOO
+"
+`;
+
+exports[`--write and --check with unknown path and no parser multiple files (stdout) 1`] = `
+"Checking formatting...
+foo.js
+Code style issues fixed in the above file(s).
+"
+`;
+
+exports[`--write and --check with unknown path and no parser multiple files (write) 1`] = `
+Array [
+  Object {
+    "content": "foo();
+",
+    "filename": "foo.js",
+  },
+]
+`;
+
+exports[`--write and --check with unknown path and no parser specific file (stderr) 1`] = `
+"[error] No parser could be inferred for file: FOO
+"
+`;
+
+exports[`--write and --check with unknown path and no parser specific file (stdout) 1`] = `
+"Checking formatting...
+All matched files use Prettier code style!
+"
+`;
+
 exports[`--write and --list-different with unknown path and no parser multiple files (stderr) 1`] = `
 "[error] No parser could be inferred for file: FOO
 "
@@ -72,6 +128,11 @@ Array [
 ]
 `;
 
+exports[`stdin no path and no parser --check logs error but exits with 0 (stderr) 1`] = `
+"[error] No parser and no file path given, couldn't infer a parser.
+"
+`;
+
 exports[`stdin no path and no parser --list-different logs error but exits with 0 (stderr) 1`] = `
 "[error] No parser and no file path given, couldn't infer a parser.
 "
@@ -82,6 +143,11 @@ exports[`stdin no path and no parser logs error and exits with 2 (stderr) 1`] =
 "
 `;
 
+exports[`stdin with unknown path and no parser --check logs error but exits with 0 (stderr) 1`] = `
+"[error] No parser could be inferred for file: foo
+"
+`;
+
 exports[`stdin with unknown path and no parser --list-different logs error but exits with 0 (stderr) 1`] = `
 "[error] No parser could be inferred for file: foo
 "

tests_integration/__tests__/__snapshots__/list-different.js.snap

@@ -1,3 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`checks stdin with --list-different (write) 1`] = `Array []`;
+
+exports[`checks stdin with -l (alias for --list-different) (write) 1`] = `Array []`;

tests_integration/__tests__/__snapshots__/piped-output.js.snap

@@ -1,5 +1,25 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`no file diffs with --check + formatted file (stderr) 1`] = `""`;
+
+exports[`no file diffs with --check + formatted file (stderr) 2`] = `""`;
+
+exports[`no file diffs with --check + formatted file (stdout) 1`] = `
+"Checking formatting...
+formatted.jsAll matched files use Prettier code style!
+"
+`;
+
+exports[`no file diffs with --check + formatted file (stdout) 2`] = `
+"Checking formatting...
+All matched files use Prettier code style!
+"
+`;
+
+exports[`no file diffs with --check + formatted file (write) 1`] = `Array []`;
+
+exports[`no file diffs with --check + formatted file (write) 2`] = `Array []`;
+
 exports[`no file diffs with --list-different + formatted file (stderr) 1`] = `""`;
 
 exports[`no file diffs with --list-different + formatted file (stderr) 2`] = `""`;
@@ -12,6 +32,44 @@ exports[`no file diffs with --list-different + formatted file (write) 1`] = `Arr
 
 exports[`no file diffs with --list-different + formatted file (write) 2`] = `Array []`;
 
+exports[`output with --check + unformatted differs when piped (stderr) 1`] = `""`;
+
+exports[`output with --check + unformatted differs when piped (stderr) 2`] = `""`;
+
+exports[`output with --check + unformatted differs when piped (stdout) 1`] = `
+"Checking formatting...
+unformatted.jsunformatted.js
+Code style issues fixed in the above file(s).
+"
+`;
+
+exports[`output with --check + unformatted differs when piped (stdout) 2`] = `
+"Checking formatting...
+unformatted.js
+Code style issues fixed in the above file(s).
+"
+`;
+
+exports[`output with --check + unformatted differs when piped (write) 1`] = `
+Array [
+  Object {
+    "content": "var x = 1;
+",
+    "filename": "unformatted.js",
+  },
+]
+`;
+
+exports[`output with --check + unformatted differs when piped (write) 2`] = `
+Array [
+  Object {
+    "content": "var x = 1;
+",
+    "filename": "unformatted.js",
+  },
+]
+`;
+
 exports[`output with --list-different + unformatted differs when piped (stderr) 1`] = `""`;
 
 exports[`output with --list-different + unformatted differs when piped (stderr) 2`] = `""`;

tests_integration/__tests__/__snapshots__/plugin-options.js.snap

@@ -5,7 +5,7 @@ exports[` 1`] = `
 - First value
 + Second value
 
-@@ -15,10 +15,12 @@
+@@ -17,10 +17,12 @@
                              Defaults to avoid.
     --no-bracket-spacing     Do not print spaces between brackets.
     --end-of-line <auto|lf|crlf|cr>

tests_integration/__tests__/__snapshots__/with-parser-inference.js.snap

@@ -14,6 +14,16 @@ exports[`infers postcss parser (stdout) 1`] = `
 
 exports[`infers postcss parser (write) 1`] = `Array []`;
 
+exports[`infers postcss parser with --check (stderr) 1`] = `""`;
+
+exports[`infers postcss parser with --check (stdout) 1`] = `
+"Checking formatting...
+All matched files use Prettier code style!
+"
+`;
+
+exports[`infers postcss parser with --check (write) 1`] = `Array []`;
+
 exports[`infers postcss parser with --list-different (stderr) 1`] = `""`;
 
 exports[`infers postcss parser with --list-different (stdout) 1`] = `""`;

tests_integration/__tests__/check.js

@@ -0,0 +1,23 @@
+"use strict";
+
+const runPrettier = require("../runPrettier");
+
+describe("checks stdin with --check", () => {
+  runPrettier("cli/with-shebang", ["--check", "--parser", "babylon"], {
+    input: "0"
+  }).test({
+    stdout: "(stdin)\n",
+    stderr: "",
+    status: "non-zero"
+  });
+});
+
+describe("checks stdin with -c (alias for --check)", () => {
+  runPrettier("cli/with-shebang", ["-c", "--parser", "babylon"], {
+    input: "0"
+  }).test({
+    stdout: "(stdin)\n",
+    stderr: "",
+    status: "non-zero"
+  });
+});

tests_integration/__tests__/debug-check.js

@@ -33,6 +33,16 @@ describe("show diff for 2+ error files with --debug-check", () => {
   });
 });
 
+describe("should not exit non-zero for already prettified code with --debug-check + --check", () => {
+  runPrettier("cli/debug-check", [
+    "issue-4599.js",
+    "--debug-check",
+    "--check"
+  ]).test({
+    status: 0
+  });
+});
+
 describe("should not exit non-zero for already prettified code with --debug-check + --list-different", () => {
   runPrettier("cli/debug-check", [
     "issue-4599.js",

tests_integration/__tests__/early-exit.js

@@ -56,6 +56,12 @@ describe("show warning with --help not-found (typo)", () => {
   });
 });
 
+describe("throw error with --check + --list-different", () => {
+  runPrettier("cli", ["--check", "--list-different"]).test({
+    status: 1
+  });
+});
+
 describe("throw error with --write + --debug-check", () => {
   runPrettier("cli", ["--write", "--debug-check"]).test({
     status: 1

tests_integration/__tests__/infer-parser.js

@@ -12,6 +12,16 @@ describe("stdin no path and no parser", () => {
     });
   });
 
+  describe("--check logs error but exits with 0", () => {
+    runPrettier("cli/infer-parser/", ["--check", "--stdin"], {
+      input: "foo"
+    }).test({
+      status: 0,
+      stdout: "",
+      write: []
+    });
+  });
+
   describe("--list-different logs error but exits with 0", () => {
     runPrettier("cli/infer-parser/", ["--list-different", "--stdin"], {
       input: "foo"
@@ -34,6 +44,18 @@ describe("stdin with unknown path and no parser", () => {
     });
   });
 
+  describe("--check logs error but exits with 0", () => {
+    runPrettier(
+      "cli/infer-parser/",
+      ["--check", "--stdin", "--stdin-filepath", "foo"],
+      { input: "foo" }
+    ).test({
+      status: 0,
+      stdout: "",
+      write: []
+    });
+  });
+
   describe("--list-different logs error but exits with 0", () => {
     runPrettier(
       "cli/infer-parser/",
@@ -64,6 +86,22 @@ describe("unknown path and no parser", () => {
   });
 });
 
+describe("--check with unknown path and no parser", () => {
+  describe("specific file", () => {
+    runPrettier("cli/infer-parser/", ["--check", "FOO"]).test({
+      status: 0,
+      write: []
+    });
+  });
+
+  describe("multiple files", () => {
+    runPrettier("cli/infer-parser/", ["--check", "*"]).test({
+      status: 1,
+      write: []
+    });
+  });
+});
+
 describe("--list-different with unknown path and no parser", () => {
   describe("specific file", () => {
     runPrettier("cli/infer-parser/", ["--list-different", "FOO"]).test({
@@ -98,6 +136,21 @@ describe("--write with unknown path and no parser", () => {
   });
 });
 
+describe("--write and --check with unknown path and no parser", () => {
+  describe("specific file", () => {
+    runPrettier("cli/infer-parser/", ["--check", "--write", "FOO"]).test({
+      status: 0,
+      write: []
+    });
+  });
+
+  describe("multiple files", () => {
+    runPrettier("cli/infer-parser/", ["--check", "--write", "*"]).test({
+      status: 0
+    });
+  });
+});
+
 describe("--write and --list-different with unknown path and no parser", () => {
   describe("specific file", () => {
     runPrettier("cli/infer-parser/", [

tests_integration/__tests__/list-different.js

@@ -11,3 +11,13 @@ describe("checks stdin with --list-different", () => {
     status: "non-zero"
   });
 });
+
+describe("checks stdin with -l (alias for --list-different)", () => {
+  runPrettier("cli/with-shebang", ["-l", "--parser", "babylon"], {
+    input: "0"
+  }).test({
+    stdout: "(stdin)\n",
+    stderr: "",
+    status: "non-zero"
+  });
+});

tests_integration/__tests__/piped-output.js

@@ -2,6 +2,49 @@
 
 const runPrettier = require("../runPrettier");
 
+describe("output with --check + unformatted differs when piped", () => {
+  const result0 = runPrettier(
+    "cli/write",
+    ["--write", "--check", "--no-color", "unformatted.js"],
+    { stdoutIsTTY: true }
+  ).test({
+    status: 0
+  });
+
+  const result1 = runPrettier(
+    "cli/write",
+    ["--write", "--check", "--no-color", "unformatted.js"],
+    { stdoutIsTTY: false }
+  ).test({
+    status: 0
+  });
+
+  expect(result0.stdout.length).toBeGreaterThan(result1.stdout.length);
+  expect(result0.write).toEqual(result1.write);
+});
+
+describe("no file diffs with --check + formatted file", () => {
+  const result0 = runPrettier(
+    "cli/write",
+    ["--write", "--check", "--no-color", "formatted.js"],
+    { stdoutIsTTY: true }
+  ).test({
+    status: 0
+  });
+
+  const result1 = runPrettier(
+    "cli/write",
+    ["--write", "--check", "--no-color", "formatted.js"],
+    { stdoutIsTTY: false }
+  ).test({
+    status: 0
+  });
+
+  expect(result0.stdout).not.toEqual(result1.stdout);
+  expect(result0.stdout.length).toBeGreaterThan(result1.stdout.length);
+  expect(result0.write).toEqual(result1.write);
+});
+
 describe("output with --list-different + unformatted differs when piped", () => {
   const result0 = runPrettier(
     "cli/write",

tests_integration/__tests__/with-parser-inference.js

@@ -9,6 +9,12 @@ describe("infers postcss parser", () => {
   });
 });
 
+describe("infers postcss parser with --check", () => {
+  runPrettier("cli/with-parser-inference", ["--check", "*"]).test({
+    status: 0
+  });
+});
+
 describe("infers postcss parser with --list-different", () => {
   runPrettier("cli/with-parser-inference", ["--list-different", "*"]).test({
     status: 0