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fix(semantic): consider update expressions in implicit returns as reads #5158

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fix(semantic): consider update expressions in implicit returns as reads #5158

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2 changes: 2 additions & 0 deletions crates/oxc_ast/src/ast/js.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1826,6 +1826,8 @@ pub struct ArrowFunctionExpression<'a> {
#[serde(flatten)]
pub span: Span,
/// Is the function body an arrow expression? i.e. `() => expr` instead of `() => {}`
///
/// When `true`, this function implicitly returns the expression.
pub expression: bool,
pub r#async: bool,
pub type_parameters: Option<Box<'a, TSTypeParameterDeclaration<'a>>>,
Expand Down
6 changes: 5 additions & 1 deletion crates/oxc_linter/src/rules/eslint/no_unused_vars/allowed.rs
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Expand Up @@ -57,7 +57,7 @@ impl<'s, 'a> Symbol<'s, 'a> {
let Some(AstKind::FunctionBody(body)) = self.nodes().parent_kind(parent.id()) else {
return false;
};
return body.span.contains_inclusive(self.span()) && body.statements.len() == 1 && !self.get_snippet(body.span).starts_with('{')
return self.is_implicit_return(body);
}
_ => {
parent.kind().debug_name();
Expand Down Expand Up @@ -103,6 +103,10 @@ impl<'s, 'a> Symbol<'s, 'a> {
.map(|node_id| nodes.get_node(node_id))
.any(|node| matches!(node.kind(), AstKind::TSModuleDeclaration(namespace) if is_ambient_namespace(namespace)))
}

pub fn is_implicit_return(&self, body: &FunctionBody) -> bool {
body.statements.len() == 1 && !self.get_snippet(body.span).starts_with('{')
}
}

#[inline]
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1 change: 1 addition & 0 deletions crates/oxc_linter/src/rules/eslint/no_unused_vars/tests/oxc.rs
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Expand Up @@ -227,6 +227,7 @@ fn test_vars_reassignment() {
",
"let i = 0; i > 0 ? 'positive' : 'negative';",
"let i = 0; i > 0 && console.log('positive');",
"export function counter() { let i = 0; return () => ++i }",
];

let fail = vec![
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13 changes: 13 additions & 0 deletions crates/oxc_semantic/src/builder.rs
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Expand Up @@ -82,6 +82,7 @@ pub struct SemanticBuilder<'a> {
// and when we reach a value declaration we set it
// to value like
pub(crate) namespace_stack: Vec<SymbolId>,
pub(crate) is_in_return: bool,
current_reference_flags: ReferenceFlags,
pub(crate) hoisting_variables: FxHashMap<ScopeId, FxHashMap<Atom<'a>, SymbolId>>,

Expand Down Expand Up @@ -134,6 +135,7 @@ impl<'a> SemanticBuilder<'a> {
current_scope_id,
function_stack: vec![],
namespace_stack: vec![],
is_in_return: false,
nodes: AstNodes::default(),
hoisting_variables: FxHashMap::default(),
scope,
Expand Down Expand Up @@ -1229,7 +1231,10 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
/* cfg */

let ret_kind = if let Some(arg) = &stmt.argument {
let in_return = self.is_in_return;
self.is_in_return = true;
self.visit_expression(arg);
self.is_in_return = in_return;
Comment on lines +1234 to +1237
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This may cause a bit of difficulty in maintaining. We should avoid writing any logic in the visit function.

ReturnInstructionKind::NotImplicitUndefined
} else {
ReturnInstructionKind::ImplicitUndefined
Expand Down Expand Up @@ -1624,7 +1629,10 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
self.visit_ts_type_annotation(return_type);
}
if let Some(body) = &func.body {
let in_return = self.is_in_return;
self.is_in_return = false;
self.visit_function_body(body);
self.is_in_return = in_return;
}

/* cfg */
Expand Down Expand Up @@ -1677,7 +1685,10 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
self.visit_ts_type_annotation(return_type);
}

let in_return = self.is_in_return;
self.is_in_return = expr.expression;
self.visit_function_body(&expr.body);
self.is_in_return = in_return;

/* cfg */
control_flow!(self, |cfg| {
Expand Down Expand Up @@ -1990,6 +2001,8 @@ impl<'a> SemanticBuilder<'a> {
fn resolve_reference_usages(&self) -> ReferenceFlags {
if self.current_reference_flags.is_empty() {
ReferenceFlags::Read
} else if self.is_in_return {
self.current_reference_flags | ReferenceFlags::Read
} else {
self.current_reference_flags
}
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48 changes: 48 additions & 0 deletions crates/oxc_semantic/tests/integration/symbols.rs
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Expand Up @@ -355,3 +355,51 @@ fn test_ts_interface_heritage() {
.has_number_of_references(1)
.test();
}

#[test]
fn test_arrow_implicit_return() {
SemanticTester::js("let i = 0; const x = () => i")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(0)
.test();

SemanticTester::js("let i = 0; const x = () => ++i")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(1)
.test();

SemanticTester::js("let i = 0; const x = () => { ++i }")
.has_root_symbol("i")
.has_number_of_reads(0)
.has_number_of_writes(1)
.test();

SemanticTester::js("let i = 0; const x = () => (0, ++i)")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(1)
.test();

SemanticTester::js("let i = 0; const x = () => (++i, 0)")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(1)
.test();
Comment on lines +385 to +389
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Is this test correct? I don't think i is being read from here (but see my general comment - I'm not sure).

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TBH, I am not sure what i ReferenceFlags should be. The x function return result is 0 when it is called, so i should be write only. I think we can try to make i only contain write if no tests are broken

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Let's try to get to the bottom of it! #5165

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IMO it's not, but there are other test cases that enforce this behavior. I mentioned this to you (@Dunqing) a while ago, when you made that change, and your rationale was that "we don't know what's a read and what's not a read, since things could be proxies and/or getters/setters"

}

#[test]
fn test_arrow_explicit_return() {
SemanticTester::js("let i = 0; const x = () => { return i }")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(0)
.test();

SemanticTester::js("let i = 0; const x = () => { return ++i }")
.has_root_symbol("i")
.has_number_of_reads(1)
.has_number_of_writes(1)
.test();
}
12 changes: 6 additions & 6 deletions tasks/coverage/semantic_babel.snap
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Expand Up @@ -154,14 +154,14 @@ after transform: ["t"]
rebuilt : []

tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/arrow-function/arrow-like-in-conditional-3/input.ts
semantic error: Unresolved references mismatch:
after transform: ["v"]
rebuilt : []
semantic error: Symbol reference IDs mismatch:
after transform: SymbolId(0): [ReferenceId(0), ReferenceId(1)]
rebuilt : SymbolId(0): [ReferenceId(0)]

tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/arrow-function/arrow-like-in-conditional-4/input.ts
semantic error: Unresolved references mismatch:
after transform: ["v"]
rebuilt : []
semantic error: Symbol reference IDs mismatch:
after transform: SymbolId(0): [ReferenceId(0)]
rebuilt : SymbolId(0): []

tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/arrow-function/async-await-null/input.ts
semantic error: Bindings mismatch:
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6 changes: 3 additions & 3 deletions tasks/coverage/semantic_typescript.snap
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Expand Up @@ -10884,9 +10884,9 @@ after transform: ScopeId(1): ["T", "i", "o"]
rebuilt : ScopeId(1): ["i", "o"]

tasks/coverage/typescript/tests/cases/compiler/inferenceLimit.ts
semantic error: Bindings mismatch:
after transform: ScopeId(0): ["BrokenClass", "MyModule"]
rebuilt : ScopeId(0): ["BrokenClass"]
semantic error: Symbol reference IDs mismatch:
after transform: SymbolId(0): [ReferenceId(2), ReferenceId(13), ReferenceId(17)]
rebuilt : SymbolId(0): []
Unresolved references mismatch:
after transform: ["Array", "Promise"]
rebuilt : ["Promise"]
Expand Down
3 changes: 2 additions & 1 deletion tasks/coverage/transformer_typescript.snap
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Expand Up @@ -2,5 +2,6 @@ commit: d8086f14

transformer_typescript Summary:
AST Parsed : 6456/6456 (100.00%)
Positive Passed: 6455/6456 (99.98%)
Positive Passed: 6454/6456 (99.97%)
Mismatch: tasks/coverage/typescript/tests/cases/compiler/inferenceLimit.ts
Mismatch: tasks/coverage/typescript/tests/cases/conformance/jsx/inline/inlineJsxAndJsxFragPragmaOverridesCompilerOptions.tsx