Expand Semantic Syntax Coverage (#17725)

Re: #17526 

## Summary
Adds tests to red knot and `linter.rs` for the semantic syntax. 

Specifically add tests for `ReboundComprehensionVariable`,
`DuplicateTypeParameter`, and `MultipleCaseAssignment`.

Refactor the `test_async_comprehension_in_sync_comprehension` →
`test_semantic_error` to be more general for all semantic syntax test
cases.

## Test Plan
This is a test.

## Question
I'm happy to contribute more tests the coming days. 

Should that happen here or should we merge this PR such that the
refactor `test_async_comprehension_in_sync_comprehension` →
`test_semantic_error` is available on main and others can chime in, too?

crates/red_knot_python_semantic/resources/mdtest/diagnostics/semantic_syntax_errors.md

@@ -130,6 +130,62 @@ async def g():
 (x async for x in g())
 ```
 
+## Rebound comprehension variable
+
+Walrus operators cannot rebind variables already in use as iterators:
+
+```py
+# error: [invalid-syntax] "assignment expression cannot rebind comprehension variable"
+[x := 2 for x in range(10)]
+
+# error: [invalid-syntax] "assignment expression cannot rebind comprehension variable"
+{y := 5 for y in range(10)}
+```
+
+## Multiple case assignments
+
+Variable names in pattern matching must be unique within a single pattern:
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+x = [1, 2]
+match x:
+    # error: [invalid-syntax] "multiple assignments to name `a` in pattern"
+    case [a, a]:
+        pass
+    case _:
+        pass
+
+d = {"key": "value"}
+match d:
+    # error: [invalid-syntax] "multiple assignments to name `b` in pattern"
+    case {"key": b, "other": b}:
+        pass
+```
+
+## Duplicate type parameter
+
+Type parameter names must be unique in a generic class or function definition:
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+# error: [invalid-syntax] "duplicate type parameter"
+class C[T, T]:
+    pass
+
+# error: [invalid-syntax] "duplicate type parameter"
+def f[X, Y, X]():
+    pass
+```
+
 ## `await` outside async function
 
 This error includes `await`, `async for`, `async with`, and `async` comprehensions.

crates/ruff_linter/src/linter.rs

@@ -1006,19 +1006,22 @@ mod tests {
     }
 
     #[test_case(
-        "error_on_310",
+        "async_in_sync_error_on_310",
         "async def f(): return [[x async for x in foo(n)] for n in range(3)]",
-        PythonVersion::PY310
+        PythonVersion::PY310,
+        "AsyncComprehensionOutsideAsyncFunction"
     )]
     #[test_case(
-        "okay_on_311",
+        "async_in_sync_okay_on_311",
         "async def f(): return [[x async for x in foo(n)] for n in range(3)]",
-        PythonVersion::PY311
+        PythonVersion::PY311,
+        "AsyncComprehensionOutsideAsyncFunction"
     )]
     #[test_case(
-        "okay_on_310",
+        "async_in_sync_okay_on_310",
         "async def test(): return [[x async for x in elements(n)] async for n in range(3)]",
-        PythonVersion::PY310
+        PythonVersion::PY310,
+        "AsyncComprehensionOutsideAsyncFunction"
     )]
     #[test_case(
         "deferred_function_body",
@@ -1028,15 +1031,46 @@ mod tests {
 			def g(): ...
 			[x async for x in foo()]
 		",
-        PythonVersion::PY310
+        PythonVersion::PY310,
+        "AsyncComprehensionOutsideAsyncFunction"
     )]
-    #[test_case("false_positive", "[x async for x in y]", PythonVersion::PY310)]
+    #[test_case(
-    fn test_async_comprehension_in_sync_comprehension(
+        "async_in_sync_false_positive",
+        "[x async for x in y]",
+        PythonVersion::PY310,
+        "AsyncComprehensionOutsideAsyncFunction"
+    )]
+    #[test_case(
+        "rebound_comprehension",
+        "[x:= 2 for x in range(2)]",
+        PythonVersion::PY310,
+        "ReboundComprehensionVariable"
+    )]
+    #[test_case(
+        "duplicate_type_param",
+        "class C[T, T]: pass",
+        PythonVersion::PY312,
+        "DuplicateTypeParameter"
+    )]
+    #[test_case(
+        "multiple_case_assignment",
+        "
+        match x:
+            case [a, a]:
+                pass
+            case _:
+                pass
+        ",
+        PythonVersion::PY310,
+        "MultipleCaseAssignment"
+    )]
+    fn test_semantic_errors(
         name: &str,
         contents: &str,
         python_version: PythonVersion,
+        error_type: &str,
     ) {
-        let snapshot = format!("async_comprehension_in_sync_comprehension_{name}_{python_version}");
+        let snapshot = format!("semantic_syntax_error_{error_type}_{name}_{python_version}");
         let messages = test_snippet_syntax_errors(
             contents,
             &LinterSettings {

crates/ruff_linter/src/snapshots/ruff_linter__linter__tests__semantic_syntax_error_AsyncComprehensionOutsideAsyncFunction_deferred_function_body_3.10.snap

@@ -1,3 +1,4 @@
 ---
 source: crates/ruff_linter/src/linter.rs
 ---
+

crates/ruff_linter/src/snapshots/ruff_linter__linter__tests__semantic_syntax_error_DuplicateTypeParameter_duplicate_type_param_3.12.snap

@@ -0,0 +1,8 @@
+---
+source: crates/ruff_linter/src/linter.rs
+---
+<filename>:1:12: SyntaxError: duplicate type parameter
+  |
+1 | class C[T, T]: pass
+  |            ^
+  |

crates/ruff_linter/src/snapshots/ruff_linter__linter__tests__semantic_syntax_error_MultipleCaseAssignment_multiple_case_assignment_3.10.snap

@@ -0,0 +1,11 @@
+---
+source: crates/ruff_linter/src/linter.rs
+---
+<filename>:3:14: SyntaxError: multiple assignments to name `a` in pattern
+  |
+2 | match x:
+3 |     case [a, a]:
+  |              ^
+4 |         pass
+5 |     case _:
+  |

crates/ruff_linter/src/snapshots/ruff_linter__linter__tests__semantic_syntax_error_ReboundComprehensionVariable_rebound_comprehension_3.10.snap

@@ -0,0 +1,8 @@
+---
+source: crates/ruff_linter/src/linter.rs
+---
+<filename>:1:2: SyntaxError: assignment expression cannot rebind comprehension variable
+  |
+1 | [x:= 2 for x in range(2)]
+  |  ^
+  |