Rename run.rs command to check.rs (#6980)

The CLI command is called "check", so this is more consistent (and
consistent with the pattern used in other commands).

crates/ruff_cli/src/commands/check_stdin.rs

@@ -0,0 +1,47 @@
+use std::io::{self, Read};
+use std::path::Path;
+
+use anyhow::Result;
+
+use ruff::packaging;
+use ruff::settings::flags;
+use ruff_workspace::resolver::{python_file_at_path, PyprojectConfig};
+
+use crate::args::Overrides;
+use crate::diagnostics::{lint_stdin, Diagnostics};
+
+/// Read a `String` from `stdin`.
+pub(crate) fn read_from_stdin() -> Result<String> {
+    let mut buffer = String::new();
+    io::stdin().lock().read_to_string(&mut buffer)?;
+    Ok(buffer)
+}
+
+/// Run the linter over a single file, read from `stdin`.
+pub(crate) fn check_stdin(
+    filename: Option<&Path>,
+    pyproject_config: &PyprojectConfig,
+    overrides: &Overrides,
+    noqa: flags::Noqa,
+    autofix: flags::FixMode,
+) -> Result<Diagnostics> {
+    if let Some(filename) = filename {
+        if !python_file_at_path(filename, pyproject_config, overrides)? {
+            return Ok(Diagnostics::default());
+        }
+    }
+    let package_root = filename.and_then(Path::parent).and_then(|path| {
+        packaging::detect_package_root(path, &pyproject_config.settings.lib.namespace_packages)
+    });
+    let stdin = read_from_stdin()?;
+    let mut diagnostics = lint_stdin(
+        filename,
+        package_root,
+        stdin,
+        &pyproject_config.settings.lib,
+        noqa,
+        autofix,
+    )?;
+    diagnostics.messages.sort_unstable();
+    Ok(diagnostics)
+}