Skip to content

feat(minifier): merge single var declarations without init into for-in #8812

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
graphite-app merged 1 commit into from
Jan 31, 2025
Merged

feat(minifier): merge single var declarations without init into for-in #8812

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 6 additions & 6 deletions crates/oxc_minifier/src/peephole/collapse_variable_declarations.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -203,16 +203,16 @@ mod test {

#[test]
fn test_for_in() {
// test("var a; for(a in b) foo()", "for (var a in b) foo()");
test("var a; for(a in b) foo()", "for (var a in b) foo()");
test("a = 0; for(a in b) foo()", "for (a in a = 0, b) foo();");
// test_same("var a = 0; for(a in b) foo()");
test_same("var a = 0; for(a in b) foo()");

// We don't handle labels yet.
// test_same("var a; a:for(a in b) foo()");
// test_same("var a; a:b:for(a in b) foo()");
test_same("var a; a:for(a in b) foo()");
test_same("var a; a:b:for(a in b) foo()");

// Verify FOR inside IFs.
// test("if(x){var a; for(a in b) foo()}", "if(x) for(var a in b) foo()");
test("if(x){var a; for(a in b) foo()}", "if(x) for(var a in b) foo()");

// Any other expression.
test("init(); for(a in b) foo()", "for (a in init(), b) foo();");
Expand All @@ -221,7 +221,7 @@ mod test {
test_same("function f(){ for(a in b) foo() }");

// We don't handle destructuring patterns yet.
// test("var a; var b; for ([a, b] in c) foo();", "var a, b; for ([a, b] in c) foo();");
test("var a; var b; for ([a, b] in c) foo();", "var a, b; for ([a, b] in c) foo();");
}

#[test]
Expand Down
81 changes: 58 additions & 23 deletions crates/oxc_minifier/src/peephole/minimize_statements.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -342,33 +342,68 @@ impl<'a> PeepholeOptimizations {
result.push(Statement::ForStatement(for_stmt));
}
Statement::ForInStatement(mut for_in_stmt) => {
// "a; for (var b in c) d" => "for (var b in a, c) d"
if let Some(Statement::ExpressionStatement(prev_expr_stmt)) = result.last_mut() {
// Annex B.3.5 allows initializers in non-strict mode
// <https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-initializers-in-forin-statement-heads>
// If there's a side-effectful initializer, we should not move the previous statement inside.
let has_side_effectful_initializer = {
if let ForStatementLeft::VariableDeclaration(var_decl) = &for_in_stmt.left {
if var_decl.declarations.len() == 1 {
// only var can have a initializer
var_decl.kind.is_var()
&& var_decl.declarations[0].init.as_ref().is_some_and(|init| {
ctx.expression_may_have_side_effects(init)
})
match result.last_mut() {
// "a; for (var b in c) d" => "for (var b in a, c) d"
Some(Statement::ExpressionStatement(prev_expr_stmt)) => {
// Annex B.3.5 allows initializers in non-strict mode
// <https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-initializers-in-forin-statement-heads>
// If there's a side-effectful initializer, we should not move the previous statement inside.
let has_side_effectful_initializer = {
if let ForStatementLeft::VariableDeclaration(var_decl) =
&for_in_stmt.left
{
if var_decl.declarations.len() == 1 {
// only var can have a initializer
var_decl.kind.is_var()
&& var_decl.declarations[0].init.as_ref().is_some_and(
|init| ctx.expression_may_have_side_effects(init),
)
} else {
// the spec does not allow multiple declarations though
true
}
} else {
// the spec does not allow multiple declarations though
true
false
}
} else {
false
};
if !has_side_effectful_initializer {
let a = &mut prev_expr_stmt.expression;
for_in_stmt.right = Self::join_sequence(a, &mut for_in_stmt.right, ctx);
result.pop();
self.mark_current_function_as_changed();
}
};
if !has_side_effectful_initializer {
let a = &mut prev_expr_stmt.expression;
for_in_stmt.right = Self::join_sequence(a, &mut for_in_stmt.right, ctx);
result.pop();
self.mark_current_function_as_changed();
}
// "var a; for (a in b) c" => "for (var a in b) c"
Some(Statement::VariableDeclaration(prev_var_decl)) => {
if let ForStatementLeft::AssignmentTargetIdentifier(id) = &for_in_stmt.left
{
let prev_var_decl_no_init_item = {
if prev_var_decl.kind.is_var()
&& prev_var_decl.declarations.len() == 1
&& prev_var_decl.declarations[0].init.is_none()
{
Some(&prev_var_decl.declarations[0])
} else {
None
}
};
if let Some(prev_var_decl_item) = prev_var_decl_no_init_item {
if let BindingPatternKind::BindingIdentifier(decl_id) =
&prev_var_decl_item.id.kind
{
if id.name == decl_id.name {
for_in_stmt.left =
ForStatementLeft::VariableDeclaration(ctx.ast.alloc(
ctx.ast.move_variable_declaration(prev_var_decl),
));
result.pop();
self.mark_current_function_as_changed();
}
}
}
}
}
_ => {}
}
result.push(Statement::ForInStatement(for_in_stmt));
}
Expand Down
Loading