Switch case goto chain is now transpiled to an elseif chain (#791)

DoctorGester · Perryvw · commit 17bb60fddb4a · 2020-01-09T20:54:52.000+01:00
* Switch case goto chain is now transpiled to an elseif chain instead of multiple ifs

* Switch case goto chain is now transpiled to an elseif chain instead of multiple ifs
diff --git a/src/transformation/visitors/switch.ts b/src/transformation/visitors/switch.ts
@@ -19,7 +19,9 @@ export const transformSwitchStatement: FunctionVisitor<ts.SwitchStatement> = (st
     let statements: lua.Statement[] = [];
 
     const caseClauses = statement.caseBlock.clauses.filter(ts.isCaseClause);
-    for (const [index, clause] of caseClauses.entries()) {
+
+    // Starting from the back, concatenating ifs into one big if/elseif statement
+    const concatenatedIf = caseClauses.reduceRight((previousCondition, clause, index) => {
         // If the clause condition holds, go to the correct label
         const condition = lua.createBinaryExpression(
             switchVariable,
@@ -28,8 +30,11 @@ export const transformSwitchStatement: FunctionVisitor<ts.SwitchStatement> = (st
         );
 
         const goto = lua.createGotoStatement(`${switchName}_case_${index}`);
-        const conditionalGoto = lua.createIfStatement(condition, lua.createBlock([goto]));
-        statements.push(conditionalGoto);
+        return lua.createIfStatement(condition, lua.createBlock([goto]), previousCondition);
+    }, undefined as lua.IfStatement | undefined);
+
+    if (concatenatedIf) {
+        statements.push(concatenatedIf);
     }
 
     const hasDefaultCase = statement.caseBlock.clauses.some(ts.isDefaultClause);
diff --git a/test/unit/__snapshots__/conditionals.spec.ts.snap b/test/unit/__snapshots__/conditionals.spec.ts.snap
@@ -0,0 +1,41 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`array 1`] = `
+"local ____exports = {}
+function ____exports.__main(self)
+    local result = -1
+    local ____switch3 = 2
+    if ____switch3 == 0 then
+        goto ____switch3_case_0
+    elseif ____switch3 == 1 then
+        goto ____switch3_case_1
+    elseif ____switch3 == 2 then
+        goto ____switch3_case_2
+    end
+    goto ____switch3_end
+    ::____switch3_case_0::
+    do
+        do
+            result = 200
+            goto ____switch3_end
+        end
+    end
+    ::____switch3_case_1::
+    do
+        do
+            result = 100
+            goto ____switch3_end
+        end
+    end
+    ::____switch3_case_2::
+    do
+        do
+            result = 1
+            goto ____switch3_end
+        end
+    end
+    ::____switch3_end::
+    return result
+end
+return ____exports"
+`;
diff --git a/test/unit/conditionals.spec.ts b/test/unit/conditionals.spec.ts
@@ -184,7 +184,7 @@ test("variable in nested scope does not interfere with case scope", () => {
     `.expectToMatchJsResult();
 });
 
-test.only("switch using variable re-declared in cases", () => {
+test("switch using variable re-declared in cases", () => {
     util.testFunction`
         let foo: number = 0;
         switch (foo) {
@@ -311,6 +311,35 @@ test.each([0, 1, 2, 3])("switchWithBracketsBreakInInternalLoop (%p)", inp => {
     `.expectToMatchJsResult();
 });
 
+test("switch uses elseif", () => {
+    test("array", () => {
+        util.testFunction`
+            let result: number = -1;
+
+            switch (2 as number) {
+                case 0: {
+                    result = 200;
+                    break;
+                }
+
+                case 1: {
+                    result = 100;
+                    break;
+                }
+
+                case 2: {
+                    result = 1;
+                    break;
+                }
+            }
+
+            return result;
+        `
+            .expectLuaToMatchSnapshot()
+            .expectToMatchJsResult();
+    });
+});
+
 test("switch not allowed in 5.1", () => {
     util.testFunction`
         switch ("abc") {}
