Repository: psf/black

Issue:
Safety checks are disabled when passing in code using `-c` / `--code`
I've been writing some docs during my documentation reorganization effort, and I've found myself writing this warning:

> --check, --diff, and --safe / --fast have no effect when using -c / --code. Safety checks normally turned on by default that verify Black's output are disabled as well.

~Is this by design? IMO it seems like an oversight / bug that should fixed.~

edit: yep this is in fact a bug, [thanks Jelle](https://github.com/psf/black/issues/2104#issuecomment-818302531)!

cc @JelleZijlstra @cooperlees 
--code doesn't work with --check or --diff
**Describe the bug**

- `--code` is supposed to take the code as an input string
- `--check` is supposed to change the exit code based on whether edits were made while formatting
- `--diff` is supposed to only output a diff, instead of the entire formatted source

What I found was the the `--check` and `--diff` flags did not work when passing input using `--code`; it behaved as if the extra flags hadn't been passed at all.

**To Reproduce** Steps to reproduce the behavior:

1. Run this command (notice the double space after `=`):

```sh
black --check --code 'a =  5'
```

2. The command exits with a status `0`, despite making edits (removing the double space).

**Expected behavior** The command should have exited with a status of `1`, since edits were made.

**Environment (please complete the following information):**

- Version: `20.8b1`
- OS and Python version: Arch Linux/Python 3.8.6



Discussion:
Seems like a bug to me. I added `-c` to make it easy to test Black's behavior without having to write a file, and testing is harder if it behaves differently from using a file.
I had a look over this. The code responsible for the `-c` behavior is:
https://github.com/psf/black/blob/b2ee211b5ad84b62738ac0997b73bf6ee9a74d06/src/black/__init__.py#L380-L382

Compared to standard formatting which does:
https://github.com/psf/black/blob/b2ee211b5ad84b62738ac0997b73bf6ee9a74d06/src/black/__init__.py#L406-L412

`write_back` and `fast` are notably missing and causing this bug. They are available at that point in the code, so they could be passed into the function.

The best way to handle this, which minimizes changes and code_repetition is to call `format_file_contents` instead of `format_str`, and add in the logic for write_back.

A sample implementation follows:
```py
    if code is not None:
        then = datetime.utcnow()
        formatted = format_file_contents(code, fast=fast, mode=mode)

        if write_back is WriteBack.CHECK:
            ctx.exit(0 if code == formatted else 1)
        elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
            now = datetime.utcnow()
            src_name = f"STDIN\t{then} +0000"
            dst_name = f"STDOUT\t{now} +0000"

            diff_contents = output.diff(code, formatted, src_name, dst_name)
            if write_back == WriteBack.COLOR_DIFF:
                diff_contents = color_diff(diff_contents)
            print(diff_contents)
        else:
            print(formatted)

        ctx.exit(0)
```

I'd like to make a PR for this if this fix seems reasonable.
Yes, that looks right. A PR would be welcome!


Resolving patch:
diff --git a/src/black/__init__.py b/src/black/__init__.py
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -384,47 +384,61 @@ def main(
     )
     if config and verbose:
         out(f"Using configuration from {config}.", bold=False, fg="blue")
+
     if code is not None:
-        print(format_str(code, mode=mode))
-        ctx.exit(0)
-    report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)
-    sources = get_sources(
-        ctx=ctx,
-        src=src,
-        quiet=quiet,
-        verbose=verbose,
-        include=include,
-        exclude=exclude,
-        extend_exclude=extend_exclude,
-        force_exclude=force_exclude,
-        report=report,
-        stdin_filename=stdin_filename,
-    )
+        # Run in quiet mode by default with -c; the extra output isn't useful.
+        # You can still pass -v to get verbose output.
+        quiet = True
 
-    path_empty(
-        sources,
-        "No Python files are present to be formatted. Nothing to do 😴",
-        quiet,
-        verbose,
-        ctx,
-    )
+    report = Report(check=check, diff=diff, quiet=quiet, verbose=verbose)
 
-    if len(sources) == 1:
-        reformat_one(
-            src=sources.pop(),
-            fast=fast,
-            write_back=write_back,
-            mode=mode,
-            report=report,
+    if code is not None:
+        reformat_code(
+            content=code, fast=fast, write_back=write_back, mode=mode, report=report
         )
     else:
-        reformat_many(
-            sources=sources, fast=fast, write_back=write_back, mode=mode, report=report
+        sources = get_sources(
+            ctx=ctx,
+            src=src,
+            quiet=quiet,
+            verbose=verbose,
+            include=include,
+            exclude=exclude,
+            extend_exclude=extend_exclude,
+            force_exclude=force_exclude,
+            report=report,
+            stdin_filename=stdin_filename,
         )
 
+        path_empty(
+            sources,
+            "No Python files are present to be formatted. Nothing to do 😴",
+            quiet,
+            verbose,
+            ctx,
+        )
+
+        if len(sources) == 1:
+            reformat_one(
+                src=sources.pop(),
+                fast=fast,
+                write_back=write_back,
+                mode=mode,
+                report=report,
+            )
+        else:
+            reformat_many(
+                sources=sources,
+                fast=fast,
+                write_back=write_back,
+                mode=mode,
+                report=report,
+            )
+
     if verbose or not quiet:
         out("Oh no! 💥 💔 💥" if report.return_code else "All done! ✨ 🍰 ✨")
-        click.secho(str(report), err=True)
+        if code is None:
+            click.secho(str(report), err=True)
     ctx.exit(report.return_code)
 
 
@@ -512,6 +526,30 @@ def path_empty(
         ctx.exit(0)
 
 
+def reformat_code(
+    content: str, fast: bool, write_back: WriteBack, mode: Mode, report: Report
+) -> None:
+    """
+    Reformat and print out `content` without spawning child processes.
+    Similar to `reformat_one`, but for string content.
+
+    `fast`, `write_back`, and `mode` options are passed to
+    :func:`format_file_in_place` or :func:`format_stdin_to_stdout`.
+    """
+    path = Path("<string>")
+    try:
+        changed = Changed.NO
+        if format_stdin_to_stdout(
+            content=content, fast=fast, write_back=write_back, mode=mode
+        ):
+            changed = Changed.YES
+        report.done(path, changed)
+    except Exception as exc:
+        if report.verbose:
+            traceback.print_exc()
+        report.failed(path, str(exc))
+
+
 def reformat_one(
     src: Path, fast: bool, write_back: WriteBack, mode: Mode, report: "Report"
 ) -> None:
@@ -720,16 +758,27 @@ def format_file_in_place(
 
 
 def format_stdin_to_stdout(
-    fast: bool, *, write_back: WriteBack = WriteBack.NO, mode: Mode
+    fast: bool,
+    *,
+    content: Optional[str] = None,
+    write_back: WriteBack = WriteBack.NO,
+    mode: Mode,
 ) -> bool:
     """Format file on stdin. Return True if changed.
 
+    If content is None, it's read from sys.stdin.
+
     If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
     write a diff to stdout. The `mode` argument is passed to
     :func:`format_file_contents`.
     """
     then = datetime.utcnow()
-    src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
+
+    if content is None:
+        src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
+    else:
+        src, encoding, newline = content, "utf-8", ""
+
     dst = src
     try:
         dst = format_file_contents(src, fast=fast, mode=mode)
@@ -743,6 +792,8 @@ def format_stdin_to_stdout(
             sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
         )
         if write_back == WriteBack.YES:
+            # Make sure there's a newline after the content
+            dst += "" if dst[-1] == "\n" else "\n"
             f.write(dst)
         elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
             now = datetime.utcnow()
diff --git a/src/black/files.py b/src/black/files.py
--- a/src/black/files.py
+++ b/src/black/files.py
@@ -38,7 +38,7 @@ def find_project_root(srcs: Sequence[str]) -> Path:
     project root, the root of the file system is returned.
     """
     if not srcs:
-        return Path("/").resolve()
+        srcs = [str(Path.cwd().resolve())]
 
     path_srcs = [Path(Path.cwd(), src).resolve() for src in srcs]
 


Test patch:
diff --git a/tests/test_black.py b/tests/test_black.py
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -34,6 +34,7 @@
 from black import Feature, TargetVersion
 from black.cache import get_cache_file
 from black.debug import DebugVisitor
+from black.output import diff, color_diff
 from black.report import Report
 import black.files
 
@@ -63,6 +64,9 @@
 T = TypeVar("T")
 R = TypeVar("R")
 
+# Match the time output in a diff, but nothing else
+DIFF_TIME = re.compile(r"\t[\d-:+\. ]+")
+
 
 @contextmanager
 def cache_dir(exists: bool = True) -> Iterator[Path]:
@@ -2069,6 +2073,146 @@ def test_docstring_reformat_for_py27(self) -> None:
         actual = result.output
         self.assertFormatEqual(actual, expected)
 
+    @staticmethod
+    def compare_results(
+        result: click.testing.Result, expected_value: str, expected_exit_code: int
+    ) -> None:
+        """Helper method to test the value and exit code of a click Result."""
+        assert (
+            result.output == expected_value
+        ), "The output did not match the expected value."
+        assert result.exit_code == expected_exit_code, "The exit code is incorrect."
+
+    def test_code_option(self) -> None:
+        """Test the code option with no changes."""
+        code = 'print("Hello world")\n'
+        args = ["--code", code]
+        result = CliRunner().invoke(black.main, args)
+
+        self.compare_results(result, code, 0)
+
+    def test_code_option_changed(self) -> None:
+        """Test the code option when changes are required."""
+        code = "print('hello world')"
+        formatted = black.format_str(code, mode=DEFAULT_MODE)
+
+        args = ["--code", code]
+        result = CliRunner().invoke(black.main, args)
+
+        self.compare_results(result, formatted, 0)
+
+    def test_code_option_check(self) -> None:
+        """Test the code option when check is passed."""
+        args = ["--check", "--code", 'print("Hello world")\n']
+        result = CliRunner().invoke(black.main, args)
+        self.compare_results(result, "", 0)
+
+    def test_code_option_check_changed(self) -> None:
+        """Test the code option when changes are required, and check is passed."""
+        args = ["--check", "--code", "print('hello world')"]
+        result = CliRunner().invoke(black.main, args)
+        self.compare_results(result, "", 1)
+
+    def test_code_option_diff(self) -> None:
+        """Test the code option when diff is passed."""
+        code = "print('hello world')"
+        formatted = black.format_str(code, mode=DEFAULT_MODE)
+        result_diff = diff(code, formatted, "STDIN", "STDOUT")
+
+        args = ["--diff", "--code", code]
+        result = CliRunner().invoke(black.main, args)
+
+        # Remove time from diff
+        output = DIFF_TIME.sub("", result.output)
+
+        assert output == result_diff, "The output did not match the expected value."
+        assert result.exit_code == 0, "The exit code is incorrect."
+
+    def test_code_option_color_diff(self) -> None:
+        """Test the code option when color and diff are passed."""
+        code = "print('hello world')"
+        formatted = black.format_str(code, mode=DEFAULT_MODE)
+
+        result_diff = diff(code, formatted, "STDIN", "STDOUT")
+        result_diff = color_diff(result_diff)
+
+        args = ["--diff", "--color", "--code", code]
+        result = CliRunner().invoke(black.main, args)
+
+        # Remove time from diff
+        output = DIFF_TIME.sub("", result.output)
+
+        assert output == result_diff, "The output did not match the expected value."
+        assert result.exit_code == 0, "The exit code is incorrect."
+
+    def test_code_option_safe(self) -> None:
+        """Test that the code option throws an error when the sanity checks fail."""
+        # Patch black.assert_equivalent to ensure the sanity checks fail
+        with patch.object(black, "assert_equivalent", side_effect=AssertionError):
+            code = 'print("Hello world")'
+            error_msg = f"{code}\nerror: cannot format <string>: \n"
+
+            args = ["--safe", "--code", code]
+            result = CliRunner().invoke(black.main, args)
+
+            self.compare_results(result, error_msg, 123)
+
+    def test_code_option_fast(self) -> None:
+        """Test that the code option ignores errors when the sanity checks fail."""
+        # Patch black.assert_equivalent to ensure the sanity checks fail
+        with patch.object(black, "assert_equivalent", side_effect=AssertionError):
+            code = 'print("Hello world")'
+            formatted = black.format_str(code, mode=DEFAULT_MODE)
+
+            args = ["--fast", "--code", code]
+            result = CliRunner().invoke(black.main, args)
+
+            self.compare_results(result, formatted, 0)
+
+    def test_code_option_config(self) -> None:
+        """
+        Test that the code option finds the pyproject.toml in the current directory.
+        """
+        with patch.object(black, "parse_pyproject_toml", return_value={}) as parse:
+            # Make sure we are in the project root with the pyproject file
+            if not Path("tests").exists():
+                os.chdir("..")
+
+            args = ["--code", "print"]
+            CliRunner().invoke(black.main, args)
+
+            pyproject_path = Path(Path().cwd(), "pyproject.toml").resolve()
+            assert (
+                len(parse.mock_calls) >= 1
+            ), "Expected config parse to be called with the current directory."
+
+            _, call_args, _ = parse.mock_calls[0]
+            assert (
+                call_args[0].lower() == str(pyproject_path).lower()
+            ), "Incorrect config loaded."
+
+    def test_code_option_parent_config(self) -> None:
+        """
+        Test that the code option finds the pyproject.toml in the parent directory.
+        """
+        with patch.object(black, "parse_pyproject_toml", return_value={}) as parse:
+            # Make sure we are in the tests directory
+            if Path("tests").exists():
+                os.chdir("tests")
+
+            args = ["--code", "print"]
+            CliRunner().invoke(black.main, args)
+
+            pyproject_path = Path(Path().cwd().parent, "pyproject.toml").resolve()
+            assert (
+                len(parse.mock_calls) >= 1
+            ), "Expected config parse to be called with the current directory."
+
+            _, call_args, _ = parse.mock_calls[0]
+            assert (
+                call_args[0].lower() == str(pyproject_path).lower()
+            ), "Incorrect config loaded."
+
 
 with open(black.__file__, "r", encoding="utf-8") as _bf:
     black_source_lines = _bf.readlines()