Refactor(Optimizer): improve typing coverage of optimizer modules by OutSquareCapital · Pull Request #7446 · tobymao/sqlglot

OutSquareCapital · 2026-04-03T07:21:04Z

Details

WIP

This is a work in progress. But since those files are very untyped ATM, it's better to split up in various passes. This is the first one, focusing on public level and simplify module.

datetime import

I changed the import datetime to from datetime import x, y, z. It's more concise when the datetime object are needed, but most importantly it's much less confusing.
Fault is on Python for sure for the API design, but since datetime is both a module and an object, and datetime.date can represent both a method and an object, IMO it's preferrable.

Partial typing

I skipped various methods/functions (or partially typed them like simplify_literals).
This is intentionnal. ATM there's various untypable behaviors, like "unsafe" non-none checks on Expr properties/args.
This would require changing the actual runtime behavior, which is out-of-scope here.

…alized`. the caller site is currently untypted anyway

… function body to avoid redundant/type unsafe double isinstance check

…y_integer_cast`. trying with overloads

… issues

…ble value

georgesittas · 2026-04-03T14:43:18Z

sqlglot/optimizer/simplify.py


    @annotate_types_on_change
-    def simplify_literals(self, expression, root=True):
+    def simplify_literals(self, expression, root: bool = True):


Should we type expression and include a return type as well here?

It wasn't really possible with the code as it was, but then I remembered that TypeIs is perfectly usable with typing_extensions , so now yes, fully typed!
This also open the door for lots of improvements at other places.
FYI, TypeIs is what ppl often think TypeGuard do

georgesittas · 2026-04-03T14:43:35Z

sqlglot/optimizer/simplify.py

-    def absorb_and_eliminate(self, expression, root=True):
+    def absorb_and_eliminate(self, expression: object, root: bool = True):


Why object? Should we add a return type?

My rule is to make the input as wide as possible and the output as narrow as possible. mypy won't let pass object as soon as we do something more specific than the likes of __eq__(), __str__(), or __dict__(), so it's permissive but strict at the same time (unlike Any for example). Narrowing the type would be incorrect as this would be an arbitrary decision. I added object as a return type tho.

georgesittas · 2026-04-03T14:43:40Z

sqlglot/optimizer/simplify.py

-    def uniq_sort(self, expression, root=True):
+    def uniq_sort(self, expression: object, root: bool = True):


Added object return type. Same logic as remove_complements

georgesittas · 2026-04-03T14:43:45Z

sqlglot/optimizer/simplify.py

-    def remove_complements(self, expression, root=True):
+    def remove_complements(self, expression: object, root: bool = True):


Added object return type. Since we can take any object and either return an Expr or the object itself.

georgesittas · 2026-04-03T14:43:53Z

sqlglot/optimizer/simplify.py

-    def _simplify_comparison(self, expression, left, right, or_=False):
+    def _simplify_comparison(
+        self, expression: exp.Expr, left: exp.Expr, right: exp.Expr, or_: bool = False
+    ):


Ditto, re: return type.

My bad, this was a miss on my part. Fixed to exp.Expr | None.

georgesittas · 2026-04-03T14:43:58Z

sqlglot/optimizer/simplify.py

+    def simplify_connectors(self, expression: exp.Expr, root: bool = True):
+        def _simplify_connectors(expression: exp.Expr, left: exp.Expr, right: exp.Expr):


Could be narrowed to -> exp.Expr thanks to the _simplify_comparison fix

georgesittas · 2026-04-03T14:44:52Z

sqlglot/optimizer/simplify.py

+
+
+def eval_boolean(
+    expression: object, a: SupportsComparison, b: SupportsComparison


Same for object.

here is a good example to explain why it's unecessary to use anything else than object:
each path will explicitely check the instance type, so it will always narrow from object to the specific check. Or else, we return None.
So really it can be any object as an input.

…rrowing

OutSquareCapital · 2026-04-03T22:15:08Z

To clarify: the goal is to gradually add types, since optimizers as a whole is a lot more untyped than the rest of the codebase.
As such, this PR scope is:

fully type the public API (exported via __init__)
Fully type "easy" functions in the simplify module
Partially annotate complex blocks with hard-to-type structure like _simplify_comparison in the simplify module

The latter will be revisited in the future, hopefully with the help of more context.
This is precisely why object is a good fit most of the time: mypy don't check the body of untyped functions, and as such we can expect to be more precise as the typing coverage progress and mypy flag object has no attribute "x" problems

OutSquareCapital added 12 commits April 3, 2026 08:27

refactor (optimizer): add various type annotations to public functions

65340ab

refactor(optimizer): add various type annotations to simplify module

11b05b8

refactor(optimizer): improve documnetation for OptimizerFn Protocol

6041213

Chore: ran ruff format

91159c5

refactor (optimizer): going back to original import pattern for `norm…

3c2eab2

…alized`. the caller site is currently untypted anyway

refactor (optimizer): make _simplify_integer_cast generic, optimize…

5d4d202

… function body to avoid redundant/type unsafe double isinstance check

fix: make S TypeVar a runtime concrete value for mypc

dfa5c17

fix: for some reason mypc don't work well with generics for `_simplif…

869f0a3

…y_integer_cast`. trying with overloads

fix: revert _simplify_integer_cast to original typing to avoid mypc…

0614a97

… issues

Fix: Use a Protocol for eval_boolean, since it can take any compara…

b967575

…ble value

Chore: run formatter

fb147b4

Refactor (optimizer): widen some helper functions input types

cb6c323

georgesittas reviewed Apr 3, 2026

View reviewed changes

OutSquareCapital added 2 commits April 3, 2026 17:16

refactor (optimizer): use TypeIs in simplify_literals for type na…

82c9193

…rrowing

chore: ruff format

08fbb54

OutSquareCapital added 7 commits April 4, 2026 00:24

fix: added various return types to simplify functions

d3da9d8

chore: ruff format

2e7dc46

fix: annotate _simplify_comparison return type

aff8bfe

refactor: add type hints to extract_interval and date_literal

4850911

Merge branch 'main' into optimizer-annotations

6ddb177

fix: widen return type of date_literal to satisfy mypc

4209d1c

Merge branch 'main' into optimizer-annotations

9c2717f

		def absorb_and_eliminate(self, expression, root=True):
		def absorb_and_eliminate(self, expression: object, root: bool = True):

		def uniq_sort(self, expression, root=True):
		def uniq_sort(self, expression: object, root: bool = True):

		def remove_complements(self, expression, root=True):
		def remove_complements(self, expression: object, root: bool = True):

		def simplify_connectors(self, expression: exp.Expr, root: bool = True):
		def _simplify_connectors(expression: exp.Expr, left: exp.Expr, right: exp.Expr):



		def eval_boolean(
		expression: object, a: SupportsComparison, b: SupportsComparison

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OutSquareCapital commented Apr 3, 2026

Details

WIP

datetime import

Partial typing

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OutSquareCapital Apr 3, 2026 •

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OutSquareCapital commented Apr 3, 2026 •

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