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[refurb] Implement readlines_in_for lint (FURB129) (#9880)
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## Summary
Implement [implicit readlines
(FURB129)](https://github.com/dosisod/refurb/blob/master/refurb/checks/iterable/implicit_readlines.py)
lint.

## Notes
I need a help/an opinion about suggested implementations.

This implementation differs from the original one from `refurb` in the
following way. This implementation checks syntactically the call of the
method with the name `readlines()` inside `for` {loop|generator
expression}. The implementation from refurb also
[checks](https://github.com/dosisod/refurb/blob/master/refurb/checks/iterable/implicit_readlines.py#L43)
that callee is a variable with a type `io.TextIOWrapper` or
`io.BufferedReader`.

- I do not see a simple way to implement the same logic.
- The best I can have is something like
```rust
checker.semantic().binding(checker.semantic().resolve_name(attr_expr.value.as_name_expr()?)?).statement(checker.semantic())
```
and analyze cases. But this will be not about types, but about guessing
the type by assignment (or with) expression.
- Also this logic has several false negatives, when the callee is not a
variable, but the result of function call (e.g. `open(...)`).
- On the other side, maybe it is good to lint this on other things,
where this suggestion is not safe, and push the developers to change
their interfaces to be less surprising, comparing with the standard
library.
- Anyway while the current implementation has false-positives (I
mentioned some of them in the test) I marked the fixes to be unsafe.
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alex-700 authored Feb 13, 2024
1 parent 609d0a9 commit dd0ba16
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67 changes: 67 additions & 0 deletions crates/ruff_linter/resources/test/fixtures/refurb/FURB129.py
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@@ -0,0 +1,67 @@
import codecs
import io
from pathlib import Path

# Errors
with open("FURB129.py") as f:
for _line in f.readlines():
pass
a = [line.lower() for line in f.readlines()]
b = {line.upper() for line in f.readlines()}
c = {line.lower(): line.upper() for line in f.readlines()}

with Path("FURB129.py").open() as f:
for _line in f.readlines():
pass

for _line in open("FURB129.py").readlines():
pass

for _line in Path("FURB129.py").open().readlines():
pass


def good1():
f = Path("FURB129.py").open()
for _line in f.readlines():
pass
f.close()


def good2(f: io.BytesIO):
for _line in f.readlines():
pass


# False positives
def bad(f):
for _line in f.readlines():
pass


def worse(f: codecs.StreamReader):
for _line in f.readlines():
pass


def foo():
class A:
def readlines(self) -> list[str]:
return ["a", "b", "c"]

return A()


for _line in foo().readlines():
pass

# OK
for _line in ["a", "b", "c"]:
pass
with open("FURB129.py") as f:
for _line in f:
pass
for _line in f.readlines(10):
pass
for _not_line in f.readline():
pass
5 changes: 4 additions & 1 deletion crates/ruff_linter/src/checkers/ast/analyze/comprehension.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,11 +2,14 @@ use ruff_python_ast::Comprehension;

use crate::checkers::ast::Checker;
use crate::codes::Rule;
use crate::rules::flake8_simplify;
use crate::rules::{flake8_simplify, refurb};

/// Run lint rules over a [`Comprehension`] syntax nodes.
pub(crate) fn comprehension(comprehension: &Comprehension, checker: &mut Checker) {
if checker.enabled(Rule::InDictKeys) {
flake8_simplify::rules::key_in_dict_comprehension(checker, comprehension);
}
if checker.enabled(Rule::ReadlinesInFor) {
refurb::rules::readlines_in_comprehension(checker, comprehension);
}
}
3 changes: 3 additions & 0 deletions crates/ruff_linter/src/checkers/ast/analyze/statement.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1317,6 +1317,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
if checker.enabled(Rule::UnnecessaryDictIndexLookup) {
pylint::rules::unnecessary_dict_index_lookup(checker, for_stmt);
}
if checker.enabled(Rule::ReadlinesInFor) {
refurb::rules::readlines_in_for(checker, for_stmt);
}
if !is_async {
if checker.enabled(Rule::ReimplementedBuiltin) {
flake8_simplify::rules::convert_for_loop_to_any_all(checker, stmt);
Expand Down
1 change: 1 addition & 0 deletions crates/ruff_linter/src/codes.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1025,6 +1025,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
#[allow(deprecated)]
(Refurb, "113") => (RuleGroup::Nursery, rules::refurb::rules::RepeatedAppend),
(Refurb, "118") => (RuleGroup::Preview, rules::refurb::rules::ReimplementedOperator),
(Refurb, "129") => (RuleGroup::Preview, rules::refurb::rules::ReadlinesInFor),
#[allow(deprecated)]
(Refurb, "131") => (RuleGroup::Nursery, rules::refurb::rules::DeleteFullSlice),
#[allow(deprecated)]
Expand Down
1 change: 1 addition & 0 deletions crates/ruff_linter/src/rules/refurb/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ mod tests {
#[test_case(Rule::ReadWholeFile, Path::new("FURB101.py"))]
#[test_case(Rule::RepeatedAppend, Path::new("FURB113.py"))]
#[test_case(Rule::ReimplementedOperator, Path::new("FURB118.py"))]
#[test_case(Rule::ReadlinesInFor, Path::new("FURB129.py"))]
#[test_case(Rule::DeleteFullSlice, Path::new("FURB131.py"))]
#[test_case(Rule::CheckAndRemoveFromSet, Path::new("FURB132.py"))]
#[test_case(Rule::IfExprMinMax, Path::new("FURB136.py"))]
Expand Down
2 changes: 2 additions & 0 deletions crates/ruff_linter/src/rules/refurb/rules/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ pub(crate) use math_constant::*;
pub(crate) use metaclass_abcmeta::*;
pub(crate) use print_empty_string::*;
pub(crate) use read_whole_file::*;
pub(crate) use readlines_in_for::*;
pub(crate) use redundant_log_base::*;
pub(crate) use regex_flag_alias::*;
pub(crate) use reimplemented_operator::*;
Expand All @@ -30,6 +31,7 @@ mod math_constant;
mod metaclass_abcmeta;
mod print_empty_string;
mod read_whole_file;
mod readlines_in_for;
mod redundant_log_base;
mod regex_flag_alias;
mod reimplemented_operator;
Expand Down
92 changes: 92 additions & 0 deletions crates/ruff_linter/src/rules/refurb/rules/readlines_in_for.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,92 @@
use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
use ruff_macros::{derive_message_formats, violation};
use ruff_python_ast::{Comprehension, Expr, StmtFor};
use ruff_python_semantic::analyze::typing;
use ruff_python_semantic::analyze::typing::is_io_base_expr;
use ruff_text_size::Ranged;

use crate::checkers::ast::Checker;

/// ## What it does
/// Checks for uses of `readlines()` when iterating over a file line-by-line.
///
/// ## Why is this bad?
/// Rather than iterating over all lines in a file by calling `readlines()`,
/// it's more convenient and performant to iterate over the file object
/// directly.
///
/// ## Example
/// ```python
/// with open("file.txt") as fp:
/// for line in fp.readlines():
/// ...
/// ```
///
/// Use instead:
/// ```python
/// with open("file.txt") as fp:
/// for line in fp:
/// ...
/// ```
///
/// ## References
/// - [Python documentation: `io.IOBase.readlines`](https://docs.python.org/3/library/io.html#io.IOBase.readlines)
#[violation]
pub(crate) struct ReadlinesInFor;

impl AlwaysFixableViolation for ReadlinesInFor {
#[derive_message_formats]
fn message(&self) -> String {
format!("Instead of calling `readlines()`, iterate over file object directly")
}

fn fix_title(&self) -> String {
"Remove `readlines()`".into()
}
}

/// FURB129
pub(crate) fn readlines_in_for(checker: &mut Checker, for_stmt: &StmtFor) {
readlines_in_iter(checker, for_stmt.iter.as_ref());
}

/// FURB129
pub(crate) fn readlines_in_comprehension(checker: &mut Checker, comprehension: &Comprehension) {
readlines_in_iter(checker, &comprehension.iter);
}

fn readlines_in_iter(checker: &mut Checker, iter_expr: &Expr) {
let Expr::Call(expr_call) = iter_expr else {
return;
};

let Expr::Attribute(expr_attr) = expr_call.func.as_ref() else {
return;
};

if expr_attr.attr.as_str() != "readlines" || !expr_call.arguments.is_empty() {
return;
}

// Determine whether `fp` in `fp.readlines()` was bound to a file object.
if let Expr::Name(name) = expr_attr.value.as_ref() {
if !checker
.semantic()
.resolve_name(name)
.map(|id| checker.semantic().binding(id))
.is_some_and(|binding| typing::is_io_base(binding, checker.semantic()))
{
return;
}
} else {
if !is_io_base_expr(expr_attr.value.as_ref(), checker.semantic()) {
return;
}
}

let mut diagnostic = Diagnostic::new(ReadlinesInFor, expr_call.range());
diagnostic.set_fix(Fix::unsafe_edit(Edit::range_deletion(
expr_call.range().add_start(expr_attr.value.range().len()),
)));
checker.diagnostics.push(diagnostic);
}
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