Add simplify-fromisoformat check (#210)

docs/categories.md

@@ -21,6 +21,11 @@ and so on.
 These checks are for the [contextlib](https://docs.python.org/3/library/contextlib.html)
 standard library module.
 
+## `datetime`
+
+These checks are for the [datetime](https://docs.python.org/3/library/datetime.html)
+standard library module.
+
 ## `decimal`
 
 These checks are for the [decimal](https://docs.python.org/3/library/decimal.html)

refurb/checks/datetime/simplify_fromisoformat.py

@@ -0,0 +1,125 @@
+from dataclasses import dataclass
+
+from mypy.nodes import (
+    CallExpr,
+    Expression,
+    IndexExpr,
+    IntExpr,
+    MemberExpr,
+    NameExpr,
+    OpExpr,
+    SliceExpr,
+    StrExpr,
+    UnaryExpr,
+    Var,
+)
+
+from refurb.error import Error
+from refurb.settings import Settings
+
+
+@dataclass
+class ErrorInfo(Error):
+    """
+    Python 3.11 adds support for parsing UTC timestamps that end with `Z`, thus
+    removing the need to strip and append the `+00:00` timezone.
+
+    Bad:
+
+    ```
+    date = "2023-02-21T02:23:15Z"
+
+    start_date = datetime.fromisoformat(date.replace("Z", "+00:00"))
+    ```
+
+    Good:
+
+    ```
+    date = "2023-02-21T02:23:15Z"
+
+    start_date = datetime.fromisoformat(date)
+    ```
+    """
+
+    name = "simplify-fromisoformat"
+    code = 162
+    categories = ["datetime", "readability"]
+
+
+def is_string(node: Expression) -> bool:
+    match node:
+        case StrExpr():
+            return True
+
+        case NameExpr(node=Var(type=ty)) if str(ty) == "builtins.str":
+            return True
+
+    return False
+
+
+def is_utc_timezone(timezone: str) -> bool:
+    return timezone.startswith(("+", "-")) and timezone.strip("+-") in (
+        "00:00",
+        "0000",
+        "00",
+    )
+
+
+def check(node: CallExpr, errors: list[Error], settings: Settings) -> None:
+    if not settings.python_version or settings.python_version < (3, 11):
+        return
+
+    match node:
+        case CallExpr(
+            callee=MemberExpr(
+                expr=NameExpr(fullname="datetime.datetime"),
+                name="fromisoformat",
+            ),
+            args=[arg],
+        ):
+            match arg:
+                case CallExpr(
+                    callee=MemberExpr(expr=date, name="replace"),
+                    args=[
+                        StrExpr(value="Z"),
+                        StrExpr(value=timezone),
+                    ],
+                ) if is_string(date) and is_utc_timezone(timezone):
+                    old = f'fromisoformat(x.replace("Z", "{timezone}"))'
+
+                case OpExpr(
+                    left=IndexExpr(
+                        base=date,
+                        index=SliceExpr(
+                            begin_index=None,
+                            end_index=UnaryExpr(op="-", expr=IntExpr(value=1)),
+                            stride=None,
+                        ),
+                    ),
+                    op="+",
+                    right=StrExpr(value=timezone),
+                ) if is_string(date) and is_utc_timezone(timezone):
+                    old = f'fromisoformat(x[:-1] + "{timezone}")'
+
+                case OpExpr(
+                    left=CallExpr(
+                        callee=MemberExpr(
+                            expr=date, name="strip" | "rstrip" as func_name
+                        ),
+                        args=[StrExpr(value="Z")],
+                    ),
+                    op="+",
+                    right=StrExpr(value=timezone),
+                ) if is_string(date) and is_utc_timezone(timezone):
+                    old = f'fromisoformat(x.{func_name}("Z") + "{timezone}")'
+
+                case _:
+                    return
+
+            errors.append(
+                ErrorInfo(
+                    node.line,
+                    node.column,
+                    f"Replace `{old}` with `fromisoformat(x)`",
+                )
+            )

test/data_3.11/err_162.py

@@ -0,0 +1,34 @@
+from datetime import datetime
+
+# these should match
+
+datetime.fromisoformat("".replace("Z", "+00:00"))
+datetime.fromisoformat("".replace("Z", "-00:00"))
+datetime.fromisoformat("".replace("Z", "+0000"))
+datetime.fromisoformat("".replace("Z", "-0000"))
+datetime.fromisoformat("".replace("Z", "+00"))
+datetime.fromisoformat("".replace("Z", "-00"))
+
+x = ""
+datetime.fromisoformat(x.replace("Z", "+00:00"))
+
+datetime.fromisoformat(""[:-1] + "+00:00")
+datetime.fromisoformat("".strip("Z") + "+00:00")
+datetime.fromisoformat("".rstrip("Z") + "+00:00")
+
+
+# these should not
+
+datetime.fromisoformat("".replace("XYZ", "+00:00"))
+datetime.fromisoformat("".replace("Z", "+10:00"))
+
+datetime.fromisoformat(""[:1] + "+00:00")
+datetime.fromisoformat(""[1:1] + "+00:00")
+datetime.fromisoformat(""[:-1:1] + "+00:00")
+
+class C:
+    def replace(self, this: str, that: str) -> str:
+        return this + that
+
+c = C()
+datetime.fromisoformat(c.replace("Z", "+00:00"))

test/data_3.11/err_162.txt

@@ -0,0 +1,10 @@
+test/data_3.11/err_162.py:5:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "+00:00"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:6:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "-00:00"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:7:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "+0000"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:8:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "-0000"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:9:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "+00"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:10:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "-00"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:13:1 [FURB162]: Replace `fromisoformat(x.replace("Z", "+00:00"))` with `fromisoformat(x)`
+test/data_3.11/err_162.py:15:1 [FURB162]: Replace `fromisoformat(x[:-1] + "+00:00")` with `fromisoformat(x)`
+test/data_3.11/err_162.py:16:1 [FURB162]: Replace `fromisoformat(x.strip("Z") + "+00:00")` with `fromisoformat(x)`
+test/data_3.11/err_162.py:17:1 [FURB162]: Replace `fromisoformat(x.rstrip("Z") + "+00:00")` with `fromisoformat(x)`

test/test_checks.py

@@ -268,6 +268,8 @@ def test_error_ignored_if_category_matches() -> None:
 def test_checks_with_python_version_dependant_error_msgs() -> None:
     run_checks_in_folder(Path("test/data_3.10"), version=(3, 10))
 
+    run_checks_in_folder(Path("test/data_3.11"), version=(3, 11))
+
 
 def run_checks_in_folder(
     folder: Path, *, version: tuple[int, int] | None = None