Update E999 to show all syntax errors (#11900)

## Summary

This PR updates the linter to show all the parse errors as diagnostics
instead of just the first one.

Note that this doesn't affect the parse error displayed as error log
message. This will be removed in a follow-up PR.

### Breaking?

I don't think this is a breaking change even though this might give more
diagnostics. The main reason is that this shouldn't affect any users
because it'll only give additional diagnostics in the case of multiple
syntax errors.

## Test Plan

Add an integration test case which would raise more than one parse
error.

Author: dhruvmanila

crates/ruff/tests/integration_test.rs

@@ -727,15 +727,32 @@ fn stdin_format_jupyter() {
 fn stdin_parse_error() {
     let mut cmd = RuffCheck::default().build();
     assert_cmd_snapshot!(cmd
-        .pass_stdin("from foo import =\n"), @r###"
+        .pass_stdin("from foo import\n"), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
-    -:1:17: E999 SyntaxError: Expected an import name
+    -:1:16: E999 SyntaxError: Expected one or more symbol names after import
     Found 1 error.
 
     ----- stderr -----
-    error: Failed to parse at 1:17: Expected an import name
+    error: Failed to parse at 1:16: Expected one or more symbol names after import
+    "###);
+}
+
+#[test]
+fn stdin_multiple_parse_error() {
+    let mut cmd = RuffCheck::default().build();
+    assert_cmd_snapshot!(cmd
+        .pass_stdin("from foo import\nbar =\n"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    -:1:16: E999 SyntaxError: Expected one or more symbol names after import
+    -:2:6: E999 SyntaxError: Expected an expression
+    Found 2 errors.
+
+    ----- stderr -----
+    error: Failed to parse at 1:16: Expected one or more symbol names after import
     "###);
 }
 

crates/ruff_linter/src/linter.rs

@@ -192,15 +192,17 @@ pub fn check_path(
                     doc_lines.extend(doc_lines_from_ast(parsed.suite(), locator));
                 }
             }
-            Err(parse_error) => {
+            Err(parse_errors) => {
                 // Always add a diagnostic for the syntax error, regardless of whether
                 // `Rule::SyntaxError` is enabled. We avoid propagating the syntax error
                 // if it's disabled via any of the usual mechanisms (e.g., `noqa`,
                 // `per-file-ignores`), and the easiest way to detect that suppression is
                 // to see if the diagnostic persists to the end of the function.
-                pycodestyle::rules::syntax_error(&mut diagnostics, parse_error, locator);
+                for parse_error in parse_errors {
+                    pycodestyle::rules::syntax_error(&mut diagnostics, parse_error, locator);
+                }
                 // TODO(dhruvmanila): Remove this clone
-                error = Some(parse_error.clone());
+                error = parse_errors.iter().next().cloned();
             }
         }
     }

crates/ruff_python_parser/src/lib.rs

@@ -274,11 +274,11 @@ impl<T> Parsed<T> {
 
     /// Returns the [`Parsed`] output as a [`Result`], returning [`Ok`] if it has no syntax errors,
     /// or [`Err`] containing the first [`ParseError`] encountered.
-    pub fn as_result(&self) -> Result<&Parsed<T>, &ParseError> {
-        if let [error, ..] = self.errors() {
-            Err(error)
-        } else {
+    pub fn as_result(&self) -> Result<&Parsed<T>, &[ParseError]> {
+        if self.is_valid() {
             Ok(self)
+        } else {
+            Err(&self.errors)
         }
     }
 

crates/ruff_python_parser/tests/fixtures.rs

@@ -126,8 +126,7 @@ fn test_invalid_syntax(input_path: &Path) {
 #[allow(clippy::print_stdout)]
 fn parser_quick_test() {
     let source = "\
-def foo()
-    pass
+from foo import
 ";
 
     let parsed = parse_unchecked(source, Mode::Module);