change parsing rule to disallow multiple else statements

Author: Shashank Shailabh

handlebars/src/main/antlr4/com/github/jknack/handlebars/internal/HbsParser.g4

@@ -74,7 +74,7 @@ block
   :
     startToken = START_BLOCK DECORATOR? sexpr blockParams? END
     thenBody=body
-    elseBlock*
+    elseBlock
     END_BLOCK nameEnd=QID END
   ;
 
@@ -97,8 +97,8 @@ sexpr
 
 elseBlock
   :
-    elseStmt
-  | elseStmtChain
+    elseStmtChain*
+    elseStmt?
   ;
 
 elseStmt

handlebars/src/main/java/com/github/jknack/handlebars/internal/TemplateBuilder.java

@@ -240,53 +240,53 @@ public Template visitBlock(final BlockContext ctx) {
     }
     // else
     Block elseroot = block;
-    for (ElseBlockContext elseBlock : ctx.elseBlock()) {
-      ElseStmtContext elseStmt = elseBlock.elseStmt();
-      if (elseStmt != null) {
-        // basic else
-        Template unless = visitBody(elseStmt.unlessBody);
-        if (unless != null) {
-          String inverseLabel = elseStmt.inverseToken.getText();
-          if (inverseLabel.startsWith(startDelim)) {
-            inverseLabel = inverseLabel.substring(startDelim.length());
-          }
-          if (inverseLabel.endsWith("~")) {
-            inverseLabel = inverseLabel.substring(0, inverseLabel.length() - 1);
-          }
-          elseroot.inverse(inverseLabel, unless);
-        }
-      } else {
-        // else chain
-        ElseStmtChainContext elseStmtChain = elseBlock.elseStmtChain();
-        SexprContext elseexpr = elseStmtChain.sexpr();
-        Token elsenameStart = elseexpr.QID().getSymbol();
-        String elsename = elsenameStart.getText();
-        String type = elseStmtChain.inverseToken.getText();
-        if (type.equals("else")) {
-          type = "else ";
-        }
-        Block elseblock =
-            new Block(
-                handlebars,
-                elsename,
-                false,
-                type,
-                params(elseexpr.param()),
-                hash(elseexpr.hash()),
-                blockParams(elseStmtChain.blockParams()));
-        elseblock.filename(source.filename());
-        elseblock.position(elsenameStart.getLine(), elsenameStart.getCharPositionInLine());
-        elseblock.startDelimiter(startDelim);
-        elseblock.endDelimiter(elseStmtChain.END().getText());
-        Template elsebody = visitBody(elseStmtChain.unlessBody);
-        elseblock.body(elsebody);
-
-        String inverseLabel = elseStmtChain.inverseToken.getText();
+    ElseBlockContext elseBlock = ctx.elseBlock();
+    ElseStmtContext elseStmt = elseBlock.elseStmt();
+    List<ElseStmtChainContext> elseStmtChain = elseBlock.elseStmtChain();
+    for (ElseStmtChainContext elseStmtChainContext : elseStmtChain) {
+      // else if chain
+      SexprContext elseexpr = elseStmtChainContext.sexpr();
+      Token elsenameStart = elseexpr.QID().getSymbol();
+      String elsename = elsenameStart.getText();
+      String type = elseStmtChainContext.inverseToken.getText();
+      if (type.equals("else")) {
+        type = "else ";
+      }
+      Block elseblock =
+          new Block(
+              handlebars,
+              elsename,
+              false,
+              type,
+              params(elseexpr.param()),
+              hash(elseexpr.hash()),
+              blockParams(elseStmtChainContext.blockParams()));
+      elseblock.filename(source.filename());
+      elseblock.position(elsenameStart.getLine(), elsenameStart.getCharPositionInLine());
+      elseblock.startDelimiter(startDelim);
+      elseblock.endDelimiter(elseStmtChainContext.END().getText());
+      Template elsebody = visitBody(elseStmtChainContext.unlessBody);
+      elseblock.body(elsebody);
+
+      String inverseLabel = elseStmtChainContext.inverseToken.getText();
+      if (inverseLabel.startsWith(startDelim)) {
+        inverseLabel = inverseLabel.substring(startDelim.length());
+      }
+      elseroot.inverse(inverseLabel, elseblock);
+      elseroot = elseblock;
+    }
+    if (elseStmt != null) {
+      // basic else
+      Template unless = visitBody(elseStmt.unlessBody);
+      if (unless != null) {
+        String inverseLabel = elseStmt.inverseToken.getText();
         if (inverseLabel.startsWith(startDelim)) {
           inverseLabel = inverseLabel.substring(startDelim.length());
         }
-        elseroot.inverse(inverseLabel, elseblock);
-        elseroot = elseblock;
+        if (inverseLabel.endsWith("~")) {
+          inverseLabel = inverseLabel.substring(0, inverseLabel.length() - 1);
+        }
+        elseroot.inverse(inverseLabel, unless);
       }
     }
     hasTag(true);

handlebars/src/test/java/com/github/jknack/handlebars/ParsingErrorTest.java

@@ -59,7 +59,9 @@ public class ParsingErrorTest extends AbstractTest {
           "idx3",
           "{{list.[]}}",
           "idx4",
-          "{{list.[}}");
+          "{{list.[}}",
+          "multipleElse",
+          "{{#if true}} b1 {{else}} b2 {{else}} b3 {{/if}}");
 
   @Test
   public void correctPath() throws IOException {
@@ -166,6 +168,11 @@ public void idx4() throws IOException {
     assertThrows(HandlebarsException.class, () -> parse("idx4"));
   }
 
+  @Test
+  public void multipleElse() throws IOException {
+    assertThrows(HandlebarsException.class, () -> parse("multipleElse"));
+  }
+
   private void parse(final String candidate) throws IOException {
     try {
       String input = (String) source.get(candidate);