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feat(minifier): prune empty case before trailing default #17994

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Merged
graphite-app merged 1 commit into from
Jan 14, 2026
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feat(minifier): prune empty case before trailing default #17994

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31 changes: 31 additions & 0 deletions crates/oxc_minifier/src/peephole/minimize_statements.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -597,6 +597,37 @@ impl<'a> PeepholeOptimizations {
result.pop();
ctx.state.changed = true;
}

// Prune empty case clauses before a trailing default
// e.g., `switch (x) { case 0: foo(); break; case 1: default: bar() }`
// => `switch (x) { case 0: foo(); break; default: bar() }`
// https://github.com/evanw/esbuild/commit/add452ed51333953dd38a26f28a775bb220ea2e9
if let Some(last_case) = switch_stmt.cases.last()
&& last_case.test.is_none()
{
let default_idx = switch_stmt.cases.len() - 1;
let mut first_empty_idx = default_idx;
// Iterate backward through preceding cases
while first_empty_idx > 0 {
let case = &switch_stmt.cases[first_empty_idx - 1];
// Only remove empty cases with primitive literal tests
if case.consequent.is_empty()
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@armano2 armano2 Jan 15, 2026 •
edited
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case that contains only break without label, block stmt, block with break could be also be considered empty

&& case.test.as_ref().is_some_and(Expression::is_literal)
{
first_empty_idx -= 1;
} else {
break;
}
}
// If we found cases to remove, keep cases [0..first_empty_idx] + [default]
if first_empty_idx < default_idx {
let default_case = switch_stmt.cases.pop().unwrap();
switch_stmt.cases.truncate(first_empty_idx);
switch_stmt.cases.push(default_case);
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@armano2 armano2 Jan 15, 2026

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default case should be ommited when its empty, either empty block or no stmt

ctx.state.changed = true;
}
}

result.push(Statement::SwitchStatement(switch_stmt));
}

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46 changes: 46 additions & 0 deletions crates/oxc_minifier/tests/peephole/esbuild.rs
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Expand Up @@ -2377,3 +2377,49 @@ fn test_remove_dead_expr_other() {
test("using x = null, y = z", "using x = null, y = z;");
test("using x = z, y = undefined", "using x = z, y = void 0;");
}

// https://github.com/evanw/esbuild/commit/add452ed51333953dd38a26f28a775bb220ea2e9
#[test]
fn prune_empty_case_before_default() {
// Basic case: empty case with literal before default
test(
"switch (x) { case 0: foo(); break; case 1: default: bar() }",
"switch (x) { case 0: foo(); break; default: bar();}",
);

// Multiple empty cases with literals before default
test(
"switch (x) { case 0: foo(); break; case 1: case 2: case 3: default: bar() }",
"switch (x) { case 0: foo(); break; default: bar();}",
);

// Empty case with non-literal (identifier) should NOT be removed
test(
"switch (x) { case 0: foo(); break; case y: default: bar() }",
"switch (x) { case 0: foo(); break; case y: default: bar();}",
);

// Empty default not at end should be preserved
test("switch (x) { default: case 1: bar() }", "switch (x) { default: case 1: bar();}");

// String literals should also be removed
test("switch (x) { case 'a': case 'b': default: bar() }", "switch (x) { default: bar();}");

// null literal (booleans get transformed to !0/!1 before this optimization runs)
test("switch (x) { case null: default: bar() }", "switch (x) { default: bar();}");

// BigInt literals
test("switch (x) { case 1n: case 2n: default: bar() }", "switch (x) { default: bar();}");

// Non-empty case should stop the pruning
test(
"switch (x) { case 0: case 1: foo(); case 2: case 3: default: bar() }",
"switch (x) { case 0: case 1: foo(); default: bar();}",
);

// Only default - nothing to prune
test("switch (x) { default: bar() }", "switch (x) { default: bar();}");

// No default - nothing to prune
test("switch (x) { case 0: foo(); case 1: }", "switch (x) { case 0: foo(); case 1:}");
}
2 changes: 1 addition & 1 deletion tasks/minsize/minsize.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -23,5 +23,5 @@ Original | minified | minified | gzip | gzip | Iterations | Fi

6.69 MB | 2.22 MB | 2.31 MB | 458.44 kB | 488.28 kB | 4 | antd.js

10.95 MB | 3.33 MB | 3.49 MB | 853.36 kB | 915.50 kB | 4 | typescript.js
10.95 MB | 3.33 MB | 3.49 MB | 853.35 kB | 915.50 kB | 4 | typescript.js

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