Modify parsing of raise with cause when exception is absent (#15049)

When confronted with `raise from exc` the parser will now create a
`StmtRaise` that has `None` for the exception and `exc` for the cause.

Before, the parser created a `StmtRaise` with `from` for the exception,
no cause, and a spurious expression `exc` afterwards.

crates/ruff_python_parser/resources/inline/err/raise_stmt_from_without_exc.py

@@ -0,0 +1,2 @@
+raise from exc
+raise from None

crates/ruff_python_parser/src/parser/statement.rs

@@ -411,9 +411,21 @@ impl<'src> Parser<'src> {
         let start = self.node_start();
         self.bump(TokenKind::Raise);
 
-        let exc = if self.at(TokenKind::Newline) {
+        let exc = match self.current_token_kind() {
+            TokenKind::Newline => None,
+            TokenKind::From => {
+                // test_err raise_stmt_from_without_exc
+                // raise from exc
+                // raise from None
+                self.add_error(
+                    ParseErrorType::OtherError(
+                        "Exception missing in `raise` statement with cause".to_string(),
+                    ),
+                    self.current_token_range(),
+                );
                 None
-        } else {
+            }
+            _ => {
                 // test_err raise_stmt_invalid_exc
                 // raise *x
                 // raise yield x
@@ -433,9 +445,10 @@ impl<'src> Parser<'src> {
                 }
 
                 Some(Box::new(exc.expr))
+            }
         };
 
-        let cause = (exc.is_some() && self.eat(TokenKind::From)).then(|| {
+        let cause = self.eat(TokenKind::From).then(|| {
             // test_err raise_stmt_invalid_cause
             // raise x from *y
             // raise x from yield y

crates/ruff_python_parser/tests/snapshots/invalid_syntax@raise_stmt_from_without_exc.py.snap

@@ -0,0 +1,57 @@
+---
+source: crates/ruff_python_parser/tests/fixtures.rs
+input_file: crates/ruff_python_parser/resources/inline/err/raise_stmt_from_without_exc.py
+---
+## AST
+
+```
+Module(
+    ModModule {
+        range: 0..31,
+        body: [
+            Raise(
+                StmtRaise {
+                    range: 0..14,
+                    exc: None,
+                    cause: Some(
+                        Name(
+                            ExprName {
+                                range: 11..14,
+                                id: Name("exc"),
+                                ctx: Load,
+                            },
+                        ),
+                    ),
+                },
+            ),
+            Raise(
+                StmtRaise {
+                    range: 15..30,
+                    exc: None,
+                    cause: Some(
+                        NoneLiteral(
+                            ExprNoneLiteral {
+                                range: 26..30,
+                            },
+                        ),
+                    ),
+                },
+            ),
+        ],
+    },
+)
+```
+## Errors
+
+  |
+1 | raise from exc
+  |       ^^^^ Syntax Error: Exception missing in `raise` statement with cause
+2 | raise from None
+  |
+
+
+  |
+1 | raise from exc
+2 | raise from None
+  |       ^^^^ Syntax Error: Exception missing in `raise` statement with cause
+  |