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[ty] Improved diagnostic for reassignments of Final symbols #19214

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merged 1 commit into from
Jul 8, 2025
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[ty] Improved diagnostic for reassignments of Final symbols #19214

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37 changes: 27 additions & 10 deletions ...ces/mdtest/snapshots/final.md_-_`typing.Final`_-_Full_diagnostics_(174fdd8134fb325b).snap
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Original file line number Diff line number Diff line change
Expand Up @@ -12,31 +12,48 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/type_qualifiers/final.md
## mdtest_snippet.py

```
1 | from typing import Final
2 |
3 | MY_CONSTANT: Final[int] = 1
4 |
5 | # more code
6 |
7 | MY_CONSTANT = 2 # error: [invalid-assignment]
1 | from typing import Final
2 |
3 | MY_CONSTANT: Final[int] = 1
4 |
5 | # more code
6 |
7 | MY_CONSTANT = 2 # error: [invalid-assignment]
8 | from _stat import ST_INO
9 |
10 | ST_INO = 1 # error: [invalid-assignment]
```

# Diagnostics

```
error[invalid-assignment]: Reassignment of `Final` symbol `MY_CONSTANT` is not allowed
--> src/mdtest_snippet.py:3:1
--> src/mdtest_snippet.py:3:14
|
1 | from typing import Final
2 |
3 | MY_CONSTANT: Final[int] = 1
| --------------------------- Original definition
| ---------- Symbol declared as `Final` here
4 |
5 | # more code
6 |
7 | MY_CONSTANT = 2 # error: [invalid-assignment]
| ^^^^^^^^^^^ Reassignment of `Final` symbol
| ^^^^^^^^^^^^^^^ Symbol later reassigned here
8 | from _stat import ST_INO
|
info: rule `invalid-assignment` is enabled by default

```

```
error[invalid-assignment]: Reassignment of `Final` symbol `ST_INO` is not allowed
--> src/mdtest_snippet.py:10:1
|
8 | from _stat import ST_INO
9 |
10 | ST_INO = 1 # error: [invalid-assignment]
| ^^^^^^^^^^ Reassignment of `Final` symbol
|
info: rule `invalid-assignment` is enabled by default

```
10 changes: 10 additions & 0 deletions crates/ty_python_semantic/resources/mdtest/type_qualifiers/final.md
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Expand Up @@ -260,6 +260,8 @@ class C:

<!-- snapshot-diagnostics -->

Annotated assignment:

```py
from typing import Final

Expand All @@ -270,4 +272,12 @@ MY_CONSTANT: Final[int] = 1
MY_CONSTANT = 2 # error: [invalid-assignment]
```

Imported `Final` symbol:

```py
from _stat import ST_INO

ST_INO = 1 # error: [invalid-assignment]
```

[`typing.final`]: https://docs.python.org/3/library/typing.html#typing.Final
28 changes: 23 additions & 5 deletions crates/ty_python_semantic/src/types/infer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1663,7 +1663,10 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {

if !is_local || previous_definition.is_some() {
let place = place_table.place_expr(binding.place(db));
if let Some(builder) = self.context.report_lint(&INVALID_ASSIGNMENT, node) {
if let Some(builder) = self.context.report_lint(
&INVALID_ASSIGNMENT,
binding.full_range(self.db(), self.module()),
) {
let mut diagnostic = builder.into_diagnostic(format_args!(
"Reassignment of `Final` symbol `{place}` is not allowed"
));
Expand All @@ -1676,10 +1679,25 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
// module, but that information is currently not threaded through attribute
// lookup.
if !previous_definition.kind(db).is_import() {
let range = previous_definition.full_range(self.db(), self.module());
diagnostic.annotate(
self.context.secondary(range).message("Original definition"),
);
if let DefinitionKind::AnnotatedAssignment(assignment) =
previous_definition.kind(db)
{
let range = assignment.annotation(self.module()).range();
diagnostic.annotate(
self.context
.secondary(range)
.message("Symbol declared as `Final` here"),
);
} else {
let range =
previous_definition.full_range(self.db(), self.module());
diagnostic.annotate(
self.context
.secondary(range)
.message("Symbol declared as `Final` here"),
);
Comment on lines +1692 to +1698
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@sharkdp sharkdp Jul 8, 2025 •
edited
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This is a fallback that currently can't be triggered, I believe, because there are no other annotated definitions that would allow a Final annotation. I guess it doesn't hurt to leave this in here, but I can also remove it.

In particular, function parameters are not allowed to be annotated with Final:

Final may only be used in assignments or variable annotations. Using it in any other position is an error. In particular, Final can’t be used in annotations for function arguments

https://typing.python.org/en/latest/spec/qualifiers.html#uppercase-final

This is something that we still have to implement (added a note to the ticket for typing.Final).

}
diagnostic.set_primary_message("Symbol later reassigned here");
}
}
}
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