red_knot_python_semantic: migrate INVALID_ASSIGNMENT for shadowing

We mostly keep things the same here, but the message has been moved from
the annotation to the diagnostic's top-line message. I think this is
perhaps a little worse, but some bigger improvements could be made here.
Indeed, we could perhaps even add a "fix" here.

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

@@ -0,0 +1,19 @@
+# Shadowing
+
+<!-- snapshot-diagnostics -->
+
+## Implicit class shadowing
+
+```py
+class C: ...
+
+C = 1  # error: [invalid-assignment]
+```
+
+## Implicit function shadowing
+
+```py
+def f(): ...
+
+f = 1  # error: [invalid-assignment]
+```

crates/red_knot_python_semantic/resources/mdtest/shadowing/class.md

@@ -5,7 +5,7 @@
 ```py
 class C: ...
 
-C = 1  # error: "Implicit shadowing of class `C`; annotate to make it explicit if this is intentional"
+C = 1  # error: "Implicit shadowing of class `C`"
 ```
 
 ## Explicit

crates/red_knot_python_semantic/resources/mdtest/shadowing/function.md

@@ -15,7 +15,7 @@ def f(x: str):
 ```py
 def f(): ...
 
-f = 1  # error: "Implicit shadowing of function `f`; annotate to make it explicit if this is intentional"
+f = 1  # error: "Implicit shadowing of function `f`"
 ```
 
 ## Explicit shadowing

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Instance_attributes_with_class-level_defaults.snap

@@ -26,13 +26,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:6:1
   |
 4 | instance = C()
 5 | instance.attr = 1  # fine
 6 | instance.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^^^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^^^^^^^^
 7 |
 8 | C.attr = 1  # fine
   |
@@ -40,12 +40,12 @@ error: lint:invalid-assignment
 ```
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:9:1
   |
 8 | C.attr = 1  # fine
 9 | C.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Pure_instance_attributes.snap

@@ -26,13 +26,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:7:1
   |
 5 | instance = C()
 6 | instance.attr = 1  # fine
 7 | instance.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^^^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^^^^^^^^
 8 |
 9 | C.attr = 1  # error: [invalid-attribute-access]
   |

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_`ClassVar`s.snap

@@ -27,12 +27,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:7:1
   |
 6 | C.attr = 1  # fine
 7 | C.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^
 8 |
 9 | instance = C()
   |

crates/red_knot_python_semantic/resources/mdtest/snapshots/shadowing.md_-_Shadowing_-_Implicit_class_shadowing.snap

@@ -0,0 +1,33 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: shadowing.md - Shadowing - Implicit class shadowing
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/shadowing.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | class C: ...
+2 | 
+3 | C = 1  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error: lint:invalid-assignment: Implicit shadowing of class `C`
+ --> /src/mdtest_snippet.py:3:1
+  |
+1 | class C: ...
+2 |
+3 | C = 1  # error: [invalid-assignment]
+  | ^
+  |
+info: Annotate to make it explicit if this is intentional
+
+```

crates/red_knot_python_semantic/resources/mdtest/snapshots/shadowing.md_-_Shadowing_-_Implicit_function_shadowing.snap

@@ -0,0 +1,33 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: shadowing.md - Shadowing - Implicit function shadowing
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/shadowing.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | def f(): ...
+2 | 
+3 | f = 1  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error: lint:invalid-assignment: Implicit shadowing of function `f`
+ --> /src/mdtest_snippet.py:3:1
+  |
+1 | def f(): ...
+2 |
+3 | f = 1  # error: [invalid-assignment]
+  | ^
+  |
+info: Annotate to make it explicit if this is intentional
+
+```

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -1116,19 +1116,26 @@ fn report_invalid_assignment_with_message(
     target_ty: Type,
     message: std::fmt::Arguments,
 ) {
+    let Some(builder) = context.report_lint(&INVALID_ASSIGNMENT, node) else {
+        return;
+    };
     match target_ty {
         Type::ClassLiteral(class) => {
-            context.report_lint_old(&INVALID_ASSIGNMENT, node, format_args!(
-                    "Implicit shadowing of class `{}`; annotate to make it explicit if this is intentional",
-                    class.name(context.db())));
+            let mut diag = builder.into_diagnostic(format_args!(
+                "Implicit shadowing of class `{}`",
+                class.name(context.db()),
+            ));
+            diag.info("Annotate to make it explicit if this is intentional");
         }
         Type::FunctionLiteral(function) => {
-            context.report_lint_old(&INVALID_ASSIGNMENT, node, format_args!(
-                    "Implicit shadowing of function `{}`; annotate to make it explicit if this is intentional",
-                    function.name(context.db())));
+            let mut diag = builder.into_diagnostic(format_args!(
+                "Implicit shadowing of function `{}`",
+                function.name(context.db()),
+            ));
+            diag.info("Annotate to make it explicit if this is intentional");
         }
         _ => {
-            context.report_lint_old(&INVALID_ASSIGNMENT, node, message);
+            builder.into_diagnostic(message);
         }
     }
 }