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Support unused variable removal in multi-assignment statements #2786

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Feb 12, 2023
Merged

Support unused variable removal in multi-assignment statements #2786

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22 changes: 22 additions & 0 deletions crates/ruff/resources/test/fixtures/pyflakes/F841_3.py
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Original file line number Diff line number Diff line change
Expand Up @@ -81,3 +81,25 @@ def f():
def f():
with Nested(m) as (x, y):
pass


def f():
toplevel = tt = lexer.get_token()
if not tt:
break


def f():
toplevel = tt = lexer.get_token()


def f():
toplevel = (a, b) = lexer.get_token()


def f():
(a, b) = toplevel = lexer.get_token()


def f():
toplevel = tt = 1
107 changes: 68 additions & 39 deletions crates/ruff/src/rules/pyflakes/rules/unused_variable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,18 +35,18 @@ impl AlwaysAutofixableViolation for UnusedVariable {

/// Return the start and end [`Location`] of the token after the next match of the predicate,
/// skipping over any bracketed expressions.
fn match_token_after<F>(stmt: &Stmt, locator: &Locator, f: F) -> Range
fn match_token_after<F, T>(located: &Located<T>, locator: &Locator, f: F) -> Range
where
F: Fn(Tok) -> bool,
{
let contents = locator.slice_source_code_range(&Range::from_located(stmt));
let contents = locator.slice_source_code_at(located.location);

// Track the bracket depth.
let mut par_count = 0;
let mut sqb_count = 0;
let mut brace_count = 0;

for ((_, tok, _), (start, _, end)) in lexer::make_tokenizer_located(contents, stmt.location)
for ((_, tok, _), (start, _, end)) in lexer::make_tokenizer_located(contents, located.location)
.flatten()
.tuple_windows()
{
Expand Down Expand Up @@ -168,43 +168,72 @@ fn remove_unused_variable(
) -> Option<(DeletionKind, Fix)> {
// First case: simple assignment (`x = 1`)
if let StmtKind::Assign { targets, value, .. } = &stmt.node {
if targets.len() == 1 && matches!(targets[0].node, ExprKind::Name { .. }) {
return if contains_effect(checker, value) {
// If the expression is complex (`x = foo()`), remove the assignment,
// but preserve the right-hand side.
Some((
DeletionKind::Partial,
Fix::deletion(
stmt.location,
match_token_after(stmt, checker.locator, |tok| tok == Tok::Equal).location,
),
))
} else {
// If (e.g.) assigning to a constant (`x = 1`), delete the entire statement.
let parent = checker
.child_to_parent
.get(&RefEquality(stmt))
.map(std::convert::Into::into);
let deleted: Vec<&Stmt> = checker
.deletions
.iter()
.map(std::convert::Into::into)
.collect();
match delete_stmt(
stmt,
parent,
&deleted,
checker.locator,
checker.indexer,
checker.stylist,
) {
Ok(fix) => Some((DeletionKind::Whole, fix)),
Err(err) => {
error!("Failed to delete unused variable: {}", err);
None
if let Some(target) = targets.iter().find(|target| {
range.location == target.location && range.end_location == target.end_location.unwrap()
}) {
if matches!(target.node, ExprKind::Name { .. }) {
return if targets.len() > 1 {
// Construct a deletion by concatenating everything before the target to
// everything after it. This ensures that our edit spans the entire statement,
// which in turn ensures that we only apply one edit per pass.
Some((
DeletionKind::Partial,
Fix::replacement(
format!(
"{}{}",
checker.locator.slice_source_code_range(&Range::new(
stmt.location,
target.location
)),
checker.locator.slice_source_code_range(&Range::new(
match_token_after(target, checker.locator, |tok| tok
== Tok::Equal)
.location,
stmt.end_location.unwrap()
))
),
stmt.location,
stmt.end_location.unwrap(),
),
))
} else if contains_effect(checker, value) {
// If the expression is complex (`x = foo()`), remove the assignment,
// but preserve the right-hand side.
Some((
DeletionKind::Partial,
Fix::deletion(
target.location,
match_token_after(target, checker.locator, |tok| tok == Tok::Equal)
.location,
),
))
} else {
// If (e.g.) assigning to a constant (`x = 1`), delete the entire statement.
let parent = checker
.child_to_parent
.get(&RefEquality(stmt))
.map(std::convert::Into::into);
let deleted: Vec<&Stmt> = checker
.deletions
.iter()
.map(std::convert::Into::into)
.collect();
match delete_stmt(
stmt,
parent,
&deleted,
checker.locator,
checker.indexer,
checker.stylist,
) {
Ok(fix) => Some((DeletionKind::Whole, fix)),
Err(err) => {
error!("Failed to delete unused variable: {}", err);
None
}
}
}
};
};
}
}
}

Expand Down
12 changes: 10 additions & 2 deletions crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F841_F841_0.py.snap
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
---
source: src/rules/pyflakes/mod.rs
source: crates/ruff/src/rules/pyflakes/mod.rs
expression: diagnostics
---
- kind:
Expand Down Expand Up @@ -90,7 +90,15 @@ expression: diagnostics
end_location:
row: 26
column: 16
fix: ~
fix:
content:
- "(x, y) = bar"
location:
row: 26
column: 4
end_location:
row: 26
column: 22
parent: ~
- kind:
UnusedVariable:
Expand Down
22 changes: 19 additions & 3 deletions crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F841_F841_1.py.snap
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
---
source: src/rules/pyflakes/mod.rs
source: crates/ruff/src/rules/pyflakes/mod.rs
expression: diagnostics
---
- kind:
Expand Down Expand Up @@ -33,7 +33,15 @@ expression: diagnostics
end_location:
row: 16
column: 19
fix: ~
fix:
content:
- "(x, y) = 1, 2"
location:
row: 16
column: 4
end_location:
row: 16
column: 26
parent: ~
- kind:
UnusedVariable:
Expand All @@ -44,7 +52,15 @@ expression: diagnostics
end_location:
row: 20
column: 10
fix: ~
fix:
content:
- "(x, y) = 1, 2"
location:
row: 20
column: 4
end_location:
row: 20
column: 26
parent: ~
- kind:
UnusedVariable:
Expand Down
153 changes: 151 additions & 2 deletions crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F841_F841_3.py.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -185,7 +185,15 @@ expression: diagnostics
end_location:
row: 33
column: 22
fix: ~
fix:
content:
- "(x2, y2) = (1, 2)"
location:
row: 33
column: 4
end_location:
row: 33
column: 31
parent: ~
- kind:
UnusedVariable:
Expand All @@ -196,7 +204,15 @@ expression: diagnostics
end_location:
row: 34
column: 11
fix: ~
fix:
content:
- "(x3, y3) = (1, 2)"
location:
row: 34
column: 4
end_location:
row: 34
column: 31
parent: ~
- kind:
UnusedVariable:
Expand Down Expand Up @@ -350,4 +366,137 @@ expression: diagnostics
row: 77
column: 27
parent: ~
- kind:
UnusedVariable:
name: toplevel
location:
row: 87
column: 4
end_location:
row: 87
column: 12
fix:
content:
- tt = lexer.get_token()
location:
row: 87
column: 4
end_location:
row: 87
column: 37
parent: ~
- kind:
UnusedVariable:
name: toplevel
location:
row: 93
column: 4
end_location:
row: 93
column: 12
fix:
content:
- tt = lexer.get_token()
location:
row: 93
column: 4
end_location:
row: 93
column: 37
parent: ~
- kind:
UnusedVariable:
name: tt
location:
row: 93
column: 15
end_location:
row: 93
column: 17
fix:
content:
- toplevel = lexer.get_token()
location:
row: 93
column: 4
end_location:
row: 93
column: 37
parent: ~
- kind:
UnusedVariable:
name: toplevel
location:
row: 97
column: 4
end_location:
row: 97
column: 12
fix:
content:
- "(a, b) = lexer.get_token()"
location:
row: 97
column: 4
end_location:
row: 97
column: 41
parent: ~
- kind:
UnusedVariable:
name: toplevel
location:
row: 101
column: 13
end_location:
row: 101
column: 21
fix:
content:
- "(a, b) = lexer.get_token()"
location:
row: 101
column: 4
end_location:
row: 101
column: 41
parent: ~
- kind:
UnusedVariable:
name: toplevel
location:
row: 105
column: 4
end_location:
row: 105
column: 12
fix:
content:
- tt = 1
location:
row: 105
column: 4
end_location:
row: 105
column: 21
parent: ~
- kind:
UnusedVariable:
name: tt
location:
row: 105
column: 15
end_location:
row: 105
column: 17
fix:
content:
- toplevel = 1
location:
row: 105
column: 4
end_location:
row: 105
column: 21
parent: ~

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