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AlexWaygood merged 2 commits into from
Aug 27, 2025
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[ty] Infer slightly more precise types for comprehensions #20111

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4ea2e30
[ty] Infer slightly more precise types for comprehensions
AlexWaygood Aug 27, 2025
41b1b1b
add regression test for fixed conformance suite issue
AlexWaygood Aug 27, 2025
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18 changes: 18 additions & 0 deletions crates/ty_python_semantic/resources/mdtest/annotations/invalid.md
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Expand Up @@ -48,6 +48,24 @@ def _(
reveal_type(h_) # revealed: Unknown
reveal_type(i_) # revealed: Unknown
reveal_type(j_) # revealed: Unknown

# Inspired by the conformance test suite at
# https://github.com/python/typing/blob/d4f39b27a4a47aac8b6d4019e1b0b5b3156fabdc/conformance/tests/aliases_implicit.py#L88-L122
B = [x for x in range(42)]
C = {x for x in range(42)}
D = {x: y for x, y in enumerate(range(42))}
E = (x for x in range(42))

def _(
b: B, # error: [invalid-type-form]
c: C, # error: [invalid-type-form]
d: D, # error: [invalid-type-form]
e: E, # error: [invalid-type-form]
):
reveal_type(b) # revealed: Unknown
reveal_type(c) # revealed: Unknown
reveal_type(d) # revealed: Unknown
reveal_type(e) # revealed: Unknown
```

## Invalid AST nodes
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2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/assignment/annotations.md
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Expand Up @@ -75,7 +75,7 @@ a: tuple[()] = (1, 2)
# error: [invalid-assignment] "Object of type `tuple[Literal["foo"]]` is not assignable to `tuple[int]`"
b: tuple[int] = ("foo",)

# error: [invalid-assignment] "Object of type `tuple[list[Unknown], Literal["foo"]]` is not assignable to `tuple[str | int, str]`"
# error: [invalid-assignment]
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@AlexWaygood AlexWaygood Aug 27, 2025

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asserting the full error message here is now slightly more complicated because Todo types are rendered differently in release builds, and our mdtest regex that usually deals with that didn't seem able to handle a Todo type nested inside two pairs of square brackets. It didn't seem essential for us to assert the full error message here, so I just simplified the test

c: tuple[str | int, str] = ([], "foo")
```

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4 changes: 2 additions & 2 deletions crates/ty_python_semantic/resources/mdtest/del.md
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Expand Up @@ -46,7 +46,7 @@ def delete():
del d # error: [unresolved-reference] "Name `d` used when not defined"

delete()
reveal_type(d) # revealed: list[Unknown]
reveal_type(d) # revealed: list[@Todo(list literal element type)]

def delete_element():
# When the `del` target isn't a name, it doesn't force local resolution.
Expand All @@ -62,7 +62,7 @@ def delete_global():

delete_global()
# Again, the variable should have been removed, but we don't check it.
reveal_type(d) # revealed: list[Unknown]
reveal_type(d) # revealed: list[@Todo(list literal element type)]

def delete_nonlocal():
e = 2
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6 changes: 0 additions & 6 deletions crates/ty_python_semantic/resources/mdtest/directives/assert_never.md
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Expand Up @@ -33,12 +33,6 @@ def _():
def _():
assert_never(None) # error: [type-assertion-failure]

def _():
assert_never([]) # error: [type-assertion-failure]

def _():
assert_never({}) # error: [type-assertion-failure]

Comment on lines -36 to -41
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@AlexWaygood AlexWaygood Aug 27, 2025

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<!-- snapshot-diagnostics --> is enabled in this section, and it gets complicated to have snapshots for diagnostics that talk about Todo types because of the fact that Todo types are rendered differently in release builds. It seemed like we already had good test coverage of assert_never() diagnostics in this section even without these lines, so I just removed them

def _():
assert_never(()) # error: [type-assertion-failure]

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2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/import/dunder_all.md
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Expand Up @@ -785,7 +785,7 @@ from subexporter import *

# TODO: Should be `list[str]`
# TODO: Should we avoid including `Unknown` for this case?
reveal_type(__all__) # revealed: Unknown | list[Unknown]
reveal_type(__all__) # revealed: Unknown | list[@Todo(list literal element type)]

__all__.append("B")

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9 changes: 8 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/literal/collections/dictionary.md
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Expand Up @@ -3,5 +3,12 @@
## Empty dictionary

```py
reveal_type({}) # revealed: dict[Unknown, Unknown]
reveal_type({}) # revealed: dict[@Todo(dict literal key type), @Todo(dict literal value type)]
```

## Dict comprehensions

```py
# revealed: dict[@Todo(dict comprehension key type), @Todo(dict comprehension value type)]
reveal_type({x: y for x, y in enumerate(range(42))})
```
6 changes: 6 additions & 0 deletions ...y_python_semantic/resources/mdtest/literal/collections/generator_expressions.md
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@@ -0,0 +1,6 @@
# Generator expressions

```py
# revealed: GeneratorType[@Todo(generator expression yield type), @Todo(generator expression send type), @Todo(generator expression return type)]
reveal_type((x for x in range(42)))
```
8 changes: 7 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/literal/collections/list.md
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Expand Up @@ -3,5 +3,11 @@
## Empty list

```py
reveal_type([]) # revealed: list[Unknown]
reveal_type([]) # revealed: list[@Todo(list literal element type)]
```

## List comprehensions

```py
reveal_type([x for x in range(42)]) # revealed: list[@Todo(list comprehension element type)]
```
8 changes: 7 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/literal/collections/set.md
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Expand Up @@ -3,5 +3,11 @@
## Basic set

```py
reveal_type({1, 2}) # revealed: set[Unknown]
reveal_type({1, 2}) # revealed: set[@Todo(set literal element type)]
```

## Set comprehensions

```py
reveal_type({x for x in range(42)}) # revealed: set[@Todo(set comprehension element type)]
```
2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/narrow/assignment.md
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Expand Up @@ -207,7 +207,7 @@ dd[0] = 0
cm: ChainMap[int, int] = ChainMap({1: 1}, {0: 0})
cm[0] = 0
# TODO: should be ChainMap[int, int]
reveal_type(cm) # revealed: ChainMap[Unknown, Unknown]
reveal_type(cm) # revealed: ChainMap[@Todo(dict literal key type), @Todo(dict literal value type)]

reveal_type(l[0]) # revealed: Literal[0]
reveal_type(d[0]) # revealed: Literal[0]
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2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/narrow/conditionals/nested.md
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Expand Up @@ -318,7 +318,7 @@ def f(l: list[str | None]):
l: list[str | None] = [None]
def _():
# TODO: should be `str | None`
reveal_type(l[0]) # revealed: Unknown
reveal_type(l[0]) # revealed: @Todo(list literal element type)

def _():
def _():
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86 changes: 23 additions & 63 deletions ...ert_never.md_-_`assert_never`_-_Basic_functionality_-_Diagnostics_(be8f5d8b0718ee54).snap
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Expand Up @@ -25,22 +25,16 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/directives/assert_never.
11 | assert_never(None) # error: [type-assertion-failure]
12 |
13 | def _():
14 | assert_never([]) # error: [type-assertion-failure]
14 | assert_never(()) # error: [type-assertion-failure]
15 |
16 | def _():
17 | assert_never({}) # error: [type-assertion-failure]
16 | def _(flag: bool, never: Never):
17 | assert_never(1 if flag else never) # error: [type-assertion-failure]
18 |
19 | def _():
20 | assert_never(()) # error: [type-assertion-failure]
19 | def _(any_: Any):
20 | assert_never(any_) # error: [type-assertion-failure]
21 |
22 | def _(flag: bool, never: Never):
23 | assert_never(1 if flag else never) # error: [type-assertion-failure]
24 |
25 | def _(any_: Any):
26 | assert_never(any_) # error: [type-assertion-failure]
27 |
28 | def _(unknown: Unknown):
29 | assert_never(unknown) # error: [type-assertion-failure]
22 | def _(unknown: Unknown):
23 | assert_never(unknown) # error: [type-assertion-failure]
```

# Diagnostics
Expand Down Expand Up @@ -101,46 +95,12 @@ error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:14:5
|
13 | def _():
14 | assert_never([]) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^--^
| |
| Inferred type of argument is `list[Unknown]`
15 |
16 | def _():
|
info: `Never` and `list[Unknown]` are not equivalent types
info: rule `type-assertion-failure` is enabled by default

```

```
error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:17:5
|
16 | def _():
17 | assert_never({}) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^--^
| |
| Inferred type of argument is `dict[Unknown, Unknown]`
18 |
19 | def _():
|
info: `Never` and `dict[Unknown, Unknown]` are not equivalent types
info: rule `type-assertion-failure` is enabled by default

```

```
error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:20:5
|
19 | def _():
20 | assert_never(()) # error: [type-assertion-failure]
14 | assert_never(()) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^--^
| |
| Inferred type of argument is `tuple[()]`
21 |
22 | def _(flag: bool, never: Never):
15 |
16 | def _(flag: bool, never: Never):
|
info: `Never` and `tuple[()]` are not equivalent types
info: rule `type-assertion-failure` is enabled by default
Expand All @@ -149,15 +109,15 @@ info: rule `type-assertion-failure` is enabled by default

```
error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:23:5
--> src/mdtest_snippet.py:17:5
|
22 | def _(flag: bool, never: Never):
23 | assert_never(1 if flag else never) # error: [type-assertion-failure]
16 | def _(flag: bool, never: Never):
17 | assert_never(1 if flag else never) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^--------------------^
| |
| Inferred type of argument is `Literal[1]`
24 |
25 | def _(any_: Any):
18 |
19 | def _(any_: Any):
|
info: `Never` and `Literal[1]` are not equivalent types
info: rule `type-assertion-failure` is enabled by default
Expand All @@ -166,15 +126,15 @@ info: rule `type-assertion-failure` is enabled by default

```
error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:26:5
--> src/mdtest_snippet.py:20:5
|
25 | def _(any_: Any):
26 | assert_never(any_) # error: [type-assertion-failure]
19 | def _(any_: Any):
20 | assert_never(any_) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^----^
| |
| Inferred type of argument is `Any`
27 |
28 | def _(unknown: Unknown):
21 |
22 | def _(unknown: Unknown):
|
info: `Never` and `Any` are not equivalent types
info: rule `type-assertion-failure` is enabled by default
Expand All @@ -183,10 +143,10 @@ info: rule `type-assertion-failure` is enabled by default

```
error[type-assertion-failure]: Argument does not have asserted type `Never`
--> src/mdtest_snippet.py:29:5
--> src/mdtest_snippet.py:23:5
|
28 | def _(unknown: Unknown):
29 | assert_never(unknown) # error: [type-assertion-failure]
22 | def _(unknown: Unknown):
23 | assert_never(unknown) # error: [type-assertion-failure]
| ^^^^^^^^^^^^^-------^
| |
| Inferred type of argument is `Unknown`
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6 changes: 3 additions & 3 deletions crates/ty_python_semantic/resources/mdtest/subscript/lists.md
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Expand Up @@ -9,13 +9,13 @@ A list can be indexed into with:

```py
x = [1, 2, 3]
reveal_type(x) # revealed: list[Unknown]
reveal_type(x) # revealed: list[@Todo(list literal element type)]

# TODO reveal int
reveal_type(x[0]) # revealed: Unknown
reveal_type(x[0]) # revealed: @Todo(list literal element type)

# TODO reveal list[int]
reveal_type(x[0:1]) # revealed: list[Unknown]
reveal_type(x[0:1]) # revealed: list[@Todo(list literal element type)]

# error: [invalid-argument-type]
reveal_type(x["a"]) # revealed: Unknown
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4 changes: 2 additions & 2 deletions crates/ty_python_semantic/resources/mdtest/type_compendium/tuple.md
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Expand Up @@ -47,9 +47,9 @@ def f(x: Iterable[int], y: list[str], z: Never, aa: list[Never]):
reveal_type(tuple((1, 2))) # revealed: tuple[Literal[1], Literal[2]]

# TODO: should be `tuple[Literal[1], ...]`
reveal_type(tuple([1])) # revealed: tuple[Unknown, ...]
reveal_type(tuple([1])) # revealed: tuple[@Todo(list literal element type), ...]

# error: [invalid-argument-type] "Argument is incorrect: Expected `tuple[int]`, found `list[Unknown]`"
# error: [invalid-argument-type]
reveal_type(tuple[int]([1])) # revealed: tuple[int]

# error: [invalid-argument-type] "Argument is incorrect: Expected `tuple[int, str]`, found `tuple[Literal[1]]`"
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4 changes: 2 additions & 2 deletions crates/ty_python_semantic/resources/mdtest/unpacking.md
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Expand Up @@ -214,8 +214,8 @@ reveal_type(d) # revealed: Literal[2]
```py
a, b = [1, 2]
# TODO: should be `int` for both `a` and `b`
reveal_type(a) # revealed: Unknown
reveal_type(b) # revealed: Unknown
reveal_type(a) # revealed: @Todo(list literal element type)
reveal_type(b) # revealed: @Todo(list literal element type)
```

### Simple unpacking
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