feat: add support for returnless FOR loops with diagnostic and semantic validation

Author: ziflex

pkg/compiler/internal/loop.go

@@ -35,7 +35,8 @@ type (
 		passThroughCtx fql.IForExpressionContext
 		kind           loopResultKind
 		distinct       bool
-		bodyCount      int
+		// bodyEnd is the exclusive end of ordinary body entries compiled before finalization.
+		bodyEnd int
 	}
 
 	loopOperandContext struct {
@@ -308,8 +309,8 @@ func (c *LoopCompiler) compileInitialization(
 func (c *LoopCompiler) resolveLoopResultSpec(ctx fql.IForExpressionContext) loopResultSpec {
 	bodies := ctx.AllForExpressionBody()
 	result := loopResultSpec{
-		kind:      loopResultEffectOnly,
-		bodyCount: len(bodies),
+		kind:    loopResultEffectOnly,
+		bodyEnd: len(bodies),
 	}
 
 	if re := ctx.ReturnExpression(); re != nil {
@@ -343,7 +344,7 @@ func (c *LoopCompiler) resolveLoopResultSpec(ctx fql.IForExpressionContext) loop
 			if nested := stmt.ForExpression(); nested != nil {
 				result.passThroughCtx = nested
 				result.kind = loopResultPassThrough
-				result.bodyCount--
+				result.bodyEnd = len(bodies) - 1
 			}
 		}
 	}
@@ -641,10 +642,10 @@ func (c *LoopCompiler) compileLoopBody(ctx fql.IForExpressionContext, resultSpec
 
 	body := ctx.AllForExpressionBody()
 
-	for i := 0; i < resultSpec.bodyCount; i++ {
-		if statement := body[i].ForExpressionStatement(); statement != nil {
+	for _, entry := range body[:resultSpec.bodyEnd] {
+		if statement := entry.ForExpressionStatement(); statement != nil {
 			c.compileForExpressionStatement(statement)
-		} else if clause := body[i].ForExpressionClause(); clause != nil {
+		} else if clause := entry.ForExpressionClause(); clause != nil {
 			c.compileForExpressionClause(clause)
 		}
 	}

test/integration/compiler/compiler_returnless_for_test.go

@@ -41,6 +41,17 @@ func TestReturnlessForValueDiagnostics(t *testing.T) {
 			query:  `RETURN FOR outer IN [1] { FOR inner IN [outer] {} }`,
 			marker: "FOR inner",
 		},
+		{
+			name: "nested pass-through operand after outer statements",
+			query: `VAR n = 0
+RETURN FOR outer IN [1] {
+  n += 1
+  FOR inner IN [outer] {
+    n += inner
+  }
+}`,
+			marker: "FOR inner",
+		},
 		{name: "while return", query: `RETURN FOR WHILE false {}`, marker: "FOR WHILE"},
 		{name: "do while return", query: `RETURN FOR DO WHILE false {}`, marker: "FOR DO"},
 	}