feat(minfier): drop last break from last switch case (#24673)

After many trial and errors, this seem to be the best way to remove
break stmts in switch cases,

This change targets only last break in last case of switch smts if its
unlabelled

this change differs from #23914 as its no longer targets all branches as
that should not be no longer necessary if all cases are correctly
rewritten

https://github.com/oxc-project/oxc/issues/24672

-----

cases like `switch (a) { case 3: if (b) break; }` are not changed

-----

ref: #17544

apps/oxlint/src-js/generated/walk.js

@@ -518,7 +518,6 @@ function walkNode(node, visitors) {
         break;
       case "TSUnionType":
         walkTSUnionType(node, visitors);
-        break;
     }
 }
 

crates/oxc_minifier/src/peephole/minimize_statements.rs

@@ -820,6 +820,12 @@ impl<'a> PeepholeOptimizations {
                 ctx,
             ));
             return;
+        } else if let Some(last_case) = switch_stmt.cases.last_mut()
+            && let Some(Statement::BreakStatement(last_break)) = last_case.consequent.last()
+            && last_break.label.is_none()
+        {
+            let dropped = last_case.consequent.pop().unwrap();
+            ctx.drop_statement(&dropped);
         }
 
         result.push(Statement::SwitchStatement(switch_stmt));

crates/oxc_minifier/tests/peephole/minimize_statements.rs

@@ -129,13 +129,13 @@ fn test_handle_switch_statement() {
     test("switch (a()) {}", "a()");
     test("switch (a) { default: }", "a;");
     test("switch (a) { default: break;}", " a;");
-    test_same("switch (a) { default: var b; break;}"); // a; var b;
+    test("switch (a) { default: var b; break;}", "switch (a) { default: var b; }"); // a; var b;
     test_same("switch (a) { default: b()}"); // a; b();
     test_same("switch (a) { default: b(); return;}"); // a, b(); return;
 
     test("switch (a) { case 1: break;}", "a;");
     test_same("switch (a) { case 1: b();}"); // a === 1 && b();
-    test_same("switch (a) { case 1: b();break; }"); // a === 1 && b();
+    test("switch (a) { case 1: b();break; }", "switch (a) { case 1: b(); }"); // a === 1 && b();
     test_same("switch (a) { case 1: b();return; }"); // if (a === 1) { b(); return; }
 
     test("switch (a) { default: case 1: }", "a;");
@@ -145,35 +145,41 @@ fn test_handle_switch_statement() {
     test_same("switch (a) { case 1: default: b(); case 2: c();}");
     test_same("switch (a) { case 1: b(); default: break; case 2: c()}");
     test_same("switch (a) { case 1: b(); case 2: break; case 3: c()}");
-    test_same("switch (a) { case 1: b(); break; case 2: c();break;}");
+    test(
+        "switch (a) { case 1: b(); break; case 2: c();break;}",
+        "switch (a) { case 1: b(); break; case 2: c();}",
+    );
     test_same("switch (x) { default: foo(); case 1: }");
     test_same("switch (a) { case 1: b(); case 2: b();}");
     test_same("switch (a) { case 1: case 2: b(); }");
-    test_same("switch (a) { case 1: var c=2; break;}"); // if (a === 1) { var c=2; }
-    test(
-        "switch (a) { case 1: case 2: default: b(); break;}",
-        "switch (a) { default: b(); break;}",
-    ); // a, b();
+    test("switch (a) { case 1: var c=2; break;}", "switch (a) { case 1: var c=2; }"); // if (a === 1) { var c=2; }
+    test("switch (a) { case 1: case 2: default: b(); break;}", "switch (a) { default: b(); }"); // a, b();
 
     test("switch (a) { default: break; case 1: break;}", "a;");
-    test_same("switch (a) { default: b();break;case 1: c();break;}"); // a === 1 ? c() : b();
+    test(
+        "switch (a) { default: b();break;case 1: c();break;}",
+        "switch (a) { default: b();break;case 1: c();}",
+    ); // a === 1 ? c() : b();
     test(
         "switch (a) { default: {b();break;} case 1: {c();break;}}",
-        "switch (a) { default: b();break;case 1: c();break;}",
+        "switch (a) { default: b();break;case 1: c(); }",
     ); // a === 1 ? c() : b();
 
     test("switch (a) { case b(): default:}", "switch (a) { case b(): }"); // a, b();
     test("switch (a) { case 2: case 1: break; default: break;}", "a;");
-    test("switch (a) { case 3: b(); break; case 2: break;}", "switch (a) { case 3: b(); break; }"); // a === 3 && b();
+    test("switch (a) { case 3: b(); break; case 2: break;}", "switch (a) { case 3: b(); }"); // a === 3 && b();
     test("switch (a) { case 3: b(); case 2: break;}", "switch (a) { case 3: b(); }"); // a === 3 && b();
-    test_same("switch (a) { case 3: b(); case 2: c(); break;}");
+    test(
+        "switch (a) { case 3: b(); case 2: c(); break;}",
+        "switch (a) { case 3: b(); case 2: c(); }",
+    );
     test("switch (a) { case 3: b(); case 2: case 1: break;}", "switch (a) { case 3: b(); }"); // a === 3 && b();
     test("switch (a) { case 3: b(); case 2: case 1: }", "switch (a) { case 3: b(); }"); // a === 3 && b();
     test_same("switch (x) { default: case 1: foo(); case 2: }"); // x !== 2 && foo();
-    test_same("switch (a) { case 3: if (b) break }"); // a === 3 && b;
+    test("switch (a) { case 3: if (b) break }", "switch (a) { case 3: if (b) break; }"); // a === 3 && b;
     test(
         "switch (a) { case 3: { if(b) {c()} else {break;} }}",
-        "switch (a) { case 3: if (b) c(); else break;}",
+        "switch (a) { case 3: if (b) c(); else break; }",
     ); // a === 3 && b && c();
     test(
         "switch (a) { case 3: { if(b) {c(); break;} else { d(); break;} }}",
@@ -189,13 +195,13 @@ fn test_handle_switch_statement() {
 
     test(
         "switch (a) { case 1: c(); case 2: default: b();break;}",
-        "switch (a) { case 1: c(); default: b(); break;}",
+        "switch (a) { case 1: c(); default: b(); }",
     ); // a === 1 && c(); b();
     test_same("function f() { switch (a) { case 1: return;} }"); // function f() { a; }
     test("switch (a()) { default: {let y;} }", "switch (a()) { default: { let y; } }"); // a(); { let y; }
     test(
         "function f(){switch ('x') { case 'x': var x = 1;break; case 'y': break; }}",
-        "function f(){switch ('x') { case 'x': var x = 1;break; }}",
+        "function f(){switch ('x') { case 'x': var x = 1; }}",
     );
     test("switch (a) { default: if(a) {break;}c();}", "switch (a) { default: if(a) break;c();}"); // a, !a && c();
     test("switch (a) { case 1: if(a) {b();}c();}", "switch (a) { case 1: a && b(), c(); }"); // if (a === 1) { a && b(), c(); }
@@ -213,26 +219,56 @@ fn test_handle_switch_statement() {
         "x: switch (a) { case 2: if (b) break outer; }",
     ); // x: if (a === 2 && b) break outer;
 
-    test_same("switch ('r') { case 'r': a();break; case 'r': var x=0;break;}"); // a();
+    test(
+        "switch ('r') { case 'r': a();break; case 'r': var x=0;break;}",
+        "switch ('r') { case 'r': a();break; case 'r': var x=0;}",
+    ); // a();
     test_same("switch (2) { default: a; case 1: b()}"); // a, b();
     test_same("switch (1) { case 1: a();break; default: b();}"); // a();
     test_same("switch ('e') { case 'e': case 'f': a();}"); // a();
-    test_same("switch ('a') { case 'a': a();break; case 'b': b();break;}"); // a();
-    test_same("switch ('c') { case 'a': a();break; case 'b': b();break;}"); // ;
-    test_same("switch (1) { case 1: a();break; case 2: bar();break;}"); // a();
+    test(
+        "switch ('a') { case 'a': a();break; case 'b': b();break;}",
+        "switch ('a') { case 'a': a();break; case 'b': b();}",
+    ); // a();
+    test(
+        "switch ('c') { case 'a': a();break; case 'b': b();break;}",
+        "switch ('c') { case 'a': a();break; case 'b': b();}",
+    ); // ;
+    test(
+        "switch (1) { case 1: a();break; case 2: bar();break;}",
+        "switch (1) { case 1: a();break; case 2: bar();}",
+    ); // a();
     test_same("switch ('f') { case 'f': a(); case 'b': b();}");
     test_same("switch ('f') { case 'f': if (a() > 0) {b();break;} c(); case 'd': f();}");
-    test_same("switch ('f') { case 'b': bar();break; case x: x();break; case 'f': f();break;}");
+    test(
+        "switch ('f') { case 'b': bar();break; case x: x();break; case 'f': f();break;}",
+        "switch ('f') { case 'b': bar();break; case x: x();break; case 'f': f(); }",
+    );
     test(
         "switch (1) { case 1: case 2: {break;} case 3: case 4: default: b(); break;}",
-        "switch (1) { case 1: case 2: break; default: b(); break; }",
+        "switch (1) { case 1: case 2: break; default: b(); }",
     );
-    test_same("switch ('d') { case 'foo': foo();break; default: bar();break;}"); // bar()
-    test_same("switch (0) { case NaN: foobar();break;case -0: foo();break; case 2: bar();break;}"); // foo()
-    test_same("let x = 1; switch ('x') { case 'x': let x = 2; break;}"); // let x = 1; { let x = 2; }
+    test(
+        "switch ('d') { case 'foo': foo();break; default: bar();break;}",
+        "switch ('d') { case 'foo': foo();break; default: bar();}",
+    ); // bar()
+    test(
+        "switch (0) { case NaN: foobar();break;case -0: foo();break; case 2: bar();break;}",
+        "switch (0) { case NaN: foobar();break;case -0: foo();break; case 2: bar();}",
+    ); // foo()
+    test(
+        "let x = 1; switch ('x') { case 'x': let x = 2; break;}",
+        "let x = 1; switch ('x') { case 'x': let x = 2; }",
+    ); // let x = 1; { let x = 2; }
     test_same("switch (1) { case 2: var x=0;}"); // if (0) var x;
-    test_same("switch (b) { case 2: switch (a) { case 2: a();break;case 3: foo();break;}}"); // ;
+    test(
+        "switch (b) { case 2: switch (a) { case 2: a();break;case 3: foo();break;}}",
+        "switch (b) { case 2: switch (a) { case 2: a();break;case 3: foo();}}",
+    ); // ;
     test_same("switch (b) { case 2: switch (a) { case 2: foo()}}"); // if (b === 2 && a === 2) foo()
 
-    test_same("function f(){ switch (0) { case x: break; } let x = 1; }"); // TDZ
+    test(
+        "function f(){ switch (0) { case x: break; } let x = 1; }",
+        "function f(){ switch (0) { case x: } let x = 1; }",
+    ); // TDZ
 }

crates/oxc_minifier/tests/peephole/obscure_edge_cases.rs

@@ -303,18 +303,24 @@ fn test_loop_optimization_edge_cases() {
 #[test]
 fn test_switch_statement_edge_cases() {
     // Test switch with constant discriminant - might be optimized in future
-    test_same("switch (2) { case 1: a(); break; case 2: b(); break; case 3: c(); break; }");
+    test_same("switch (2) { case 1: a(); break; case 2: b(); break; case 3: c(); }");
     // Could be optimized to just: b();
 
     test_same("switch ('test') { case 'foo': a(); break; case 'test': b(); break; default: c(); }");
     // Could be optimized to just: b();
 
     // Test switch with no matching case
-    test_same("switch (5) { case 1: a(); break; case 2: b(); break; }");
+    test(
+        "switch (5) { case 1: a(); break; case 2: b(); break; }",
+        "switch (5) { case 1: a(); break; case 2: b(); }",
+    );
     // Could be optimized to empty
 
     // Test switch with default
-    test_same("switch (5) { case 1: a(); break; default: b(); break; }");
+    test(
+        "switch (5) { case 1: a(); break; default: b(); break; }",
+        "switch (5) { case 1: a(); break; default: b(); }",
+    );
     // Could be optimized to just: b();
 
     // Test switch with fall-through - more complex, keep as same for safety

napi/parser/src-js/generated/visit/walk.js

@@ -504,7 +504,6 @@ function walkNode(node, visitors) {
         break;
       case "TSUnionType":
         walkTSUnionType(node, visitors);
-        break;
     }
 }
 

tasks/minsize/minsize.snap

@@ -3,25 +3,25 @@ Original   | minified   | minified   | gzip       | gzip       | Iterations | Fi
 -------------------------------------------------------------------------------------
 72.14 kB   | 23.12 kB   | 23.70 kB   | 8.34 kB    | 8.54 kB    |          2 | react.development.js 
 
-173.90 kB  | 59.40 kB   | 59.82 kB   | 19.15 kB   | 19.33 kB   |          2 | moment.js  
+173.90 kB  | 59.37 kB   | 59.82 kB   | 19.15 kB   | 19.33 kB   |          2 | moment.js  
 
 287.63 kB  | 89.24 kB   | 90.07 kB   | 30.91 kB   | 31.95 kB   |          2 | jquery.js  
 
-342.15 kB  | 116.97 kB  | 118.14 kB  | 43.17 kB   | 44.37 kB   |          2 | vue.js     
+342.15 kB  | 116.95 kB  | 118.14 kB  | 43.17 kB   | 44.37 kB   |          2 | vue.js     
 
-544.10 kB  | 70.92 kB   | 72.48 kB   | 25.73 kB   | 26.20 kB   |          2 | lodash.js  
+544.10 kB  | 70.91 kB   | 72.48 kB   | 25.73 kB   | 26.20 kB   |          2 | lodash.js  
 
-555.77 kB  | 267.38 kB  | 270.13 kB  | 88.00 kB   | 90.80 kB   |          2 | d3.js      
+555.77 kB  | 267.20 kB  | 270.13 kB  | 87.98 kB   | 90.80 kB   |          2 | d3.js      
 
-1.01 MB    | 439.33 kB  | 458.89 kB  | 122.04 kB  | 126.71 kB  |          2 | bundle.min.js 
+1.01 MB    | 439.29 kB  | 458.89 kB  | 122.05 kB  | 126.71 kB  |          2 | bundle.min.js 
 
-1.25 MB    | 642.61 kB  | 646.76 kB  | 159.40 kB  | 163.73 kB  |          2 | three.js   
+1.25 MB    | 642.52 kB  | 646.76 kB  | 159.39 kB  | 163.73 kB  |          2 | three.js   
 
-2.14 MB    | 711.03 kB  | 724.14 kB  | 160.38 kB  | 181.07 kB  |          2 | victory.js 
+2.14 MB    | 710.90 kB  | 724.14 kB  | 160.38 kB  | 181.07 kB  |          2 | victory.js 
 
-3.20 MB    | 1.00 MB    | 1.01 MB    | 322.59 kB  | 331.56 kB  |          2 | echarts.js 
+3.20 MB    | 1.00 MB    | 1.01 MB    | 322.56 kB  | 331.56 kB  |          2 | echarts.js 
 
-6.69 MB    | 2.12 MB    | 2.31 MB    | 453.85 kB  | 488.28 kB  |          5 | antd.js    
+6.69 MB    | 2.12 MB    | 2.31 MB    | 453.83 kB  | 488.28 kB  |          5 | antd.js    
 
-10.95 MB   | 3.33 MB    | 3.49 MB    | 853.03 kB  | 915.50 kB  |          4 | typescript.js 
+10.95 MB   | 3.33 MB    | 3.49 MB    | 852.92 kB  | 915.50 kB  |          4 | typescript.js 
 

tasks/track_memory_allocations/allocs_minifier.yaml

@@ -5,9 +5,9 @@ checker.ts:
   sys deallocs: 152
   sys alloc bytes: 15028748 # 15.03 MB
   sys peak growth: 10203896 # 10.20 MB
-  arena allocs: 152763
-  arena reallocs: 28276
-  arena size: 19312968 # 19.31 MB
+  arena allocs: 152706
+  arena reallocs: 28225
+  arena size: 19309904 # 19.31 MB
 
 App.tsx:
   file size: 415342 # 415.34 kB
@@ -16,8 +16,8 @@ App.tsx:
   sys deallocs: 63
   sys alloc bytes: 2136669 # 2.14 MB
   sys peak growth: 1620605 # 1.62 MB
-  arena allocs: 17029
-  arena reallocs: 2702
+  arena allocs: 17027
+  arena reallocs: 2700
   arena size: 2915736 # 2.92 MB
 
 RadixUIAdoptionSection.jsx:
@@ -38,9 +38,9 @@ pdf.mjs:
   sys deallocs: 2467
   sys alloc bytes: 5348727 # 5.35 MB
   sys peak growth: 3707391 # 3.71 MB
-  arena allocs: 47452
-  arena reallocs: 7743
-  arena size: 6375424 # 6.38 MB
+  arena allocs: 47424
+  arena reallocs: 7715
+  arena size: 6374064 # 6.37 MB
 
 antd.js:
   file size: 6686316 # 6.69 MB
@@ -49,9 +49,9 @@ antd.js:
   sys deallocs: 1038
   sys alloc bytes: 29987563 # 29.99 MB
   sys peak growth: 19934725 # 19.93 MB
-  arena allocs: 371535
-  arena reallocs: 76376
-  arena size: 49107608 # 49.11 MB
+  arena allocs: 371435
+  arena reallocs: 76276
+  arena size: 49102648 # 49.10 MB
 
 binder.ts:
   file size: 193077 # 193.08 kB
@@ -60,8 +60,8 @@ binder.ts:
   sys deallocs: 33
   sys alloc bytes: 963614 # 963.61 kB
   sys peak growth: 658042 # 658.04 kB
-  arena allocs: 7084
-  arena reallocs: 840
+  arena allocs: 7082
+  arena reallocs: 838
   arena size: 1169808 # 1.17 MB
 
 kitchen-sink.tsx:
@@ -71,7 +71,7 @@ kitchen-sink.tsx:
   sys deallocs: 1867
   sys alloc bytes: 5346850 # 5.35 MB
   sys peak growth: 3738631 # 3.74 MB
-  arena allocs: 71947
-  arena reallocs: 12262
+  arena allocs: 71929
+  arena reallocs: 12244
   arena size: 9560960 # 9.56 MB