Fix/dead code after break (#1694)

RealColdFry · web-flow · commit 2bb18e12b035 · 2026-03-28T13:55:05.000+01:00
* strip dead code after break in printer

* change tests from translation to no execution error

* remove unused expectAllVersions

* improve break dead code tests: target affected versions, check output values
diff --git a/src/LuaPrinter.ts b/src/LuaPrinter.ts
@@ -328,7 +328,7 @@ export class LuaPrinter {
 
             statementNodes.push(node);
 
-            if (lua.isReturnStatement(statement)) break;
+            if (lua.isReturnStatement(statement) || lua.isBreakStatement(statement)) break;
         }
 
         return statementNodes.length > 0 ? [...intersperse<SourceChunk>(statementNodes, "\n"), "\n"] : [];
diff --git a/test/unit/printer/deadCodeAfterBreak.spec.ts b/test/unit/printer/deadCodeAfterBreak.spec.ts
@@ -0,0 +1,93 @@
+import * as tstl from "../../../src";
+import * as util from "../../util";
+
+// In Lua 5.0, 5.1, and LuaJIT, break must be the last statement in a block.
+// Any code after break is a syntax error (e.g. `while true do break; local b = 8 end`
+// fails with "'end' expected near 'local'"). Lua 5.2+ relaxed this restriction.
+// TSTL should strip dead code after break on all targets to avoid these errors.
+
+function expectNoDeadCode(builder: util.TestBuilder) {
+    const lua = builder.getMainLuaCodeChunk();
+    expect(lua).not.toContain("local b = 8");
+}
+
+const affectedVersions: Record<tstl.LuaTarget, ((builder: util.TestBuilder) => void) | boolean> = {
+    [tstl.LuaTarget.Universal]: false,
+    [tstl.LuaTarget.Lua50]: builder => builder.tap(expectNoDeadCode).expectToMatchJsResult(),
+    [tstl.LuaTarget.Lua51]: builder => builder.tap(expectNoDeadCode).expectToMatchJsResult(),
+    [tstl.LuaTarget.Lua52]: false,
+    [tstl.LuaTarget.Lua53]: false,
+    [tstl.LuaTarget.Lua54]: false,
+    [tstl.LuaTarget.Lua55]: false,
+    [tstl.LuaTarget.LuaJIT]: builder => builder.tap(expectNoDeadCode),
+    [tstl.LuaTarget.Luau]: false,
+};
+
+util.testEachVersion(
+    "for dead code after break",
+    () => util.testFunction`
+        let result = 0;
+        for (let i = 0; i < 10; i++) { result = i; break; const b = 8; }
+        return result;
+    `,
+    affectedVersions
+);
+
+util.testEachVersion(
+    "for..in dead code after break",
+    () => util.testFunction`
+        let result = "";
+        for (let a in {"a": 5, "b": 8}) { result = a; break; const b = 8; }
+        return result;
+    `,
+    affectedVersions
+);
+
+util.testEachVersion(
+    "for..of dead code after break",
+    () => util.testFunction`
+        let result = 0;
+        for (let a of [1,2,4]) { result = a; break; const b = 8; }
+        return result;
+    `,
+    affectedVersions
+);
+
+util.testEachVersion(
+    "while dead code after break",
+    () => util.testFunction`
+        let result = "done";
+        while (true) { break; const b = 8; }
+        return result;
+    `,
+    affectedVersions
+);
+
+util.testEachVersion(
+    "switch dead code after break",
+    () => util.testFunction`
+        let result = "none";
+        switch ("abc" as string) {
+            case "def":
+                result = "def";
+                break;
+                let abc = 4;
+            case "abc":
+                result = "abc";
+                break;
+                let def = 6;
+        }
+        return result;
+    `,
+    affectedVersions
+);
+
+util.testEachVersion(
+    "do-while dead code after break",
+    () => util.testFunction`
+        let result = "done";
+        do { break; const b = 8; } while (true);
+        return result;
+    `,
+    affectedVersions
+);

Original file line number	Diff line number	Diff line change
`@@ -328,7 +328,7 @@ export class LuaPrinter {`
`328`	`328`
`329`	`329`	`statementNodes.push(node);`
`330`	`330`
`331`		`- if (lua.isReturnStatement(statement)) break;`
	`331`	`+ if (lua.isReturnStatement(statement) \|\| lua.isBreakStatement(statement)) break;`
`332`	`332`	`}`
`333`	`333`
`334`	`334`	`return statementNodes.length > 0 ? [...intersperse<SourceChunk>(statementNodes, "\n"), "\n"] : [];`