From 2c967dd24e63b388479c71f2648418c14f7b94b7 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 19 Nov 2023 14:50:40 +0900
Subject: [PATCH] internal/shader: bug fix: variables in an index should be
 marked as used

Closes #2848
---
 internal/shader/expr.go        |  2 +-
 internal/shader/syntax_test.go | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/internal/shader/expr.go b/internal/shader/expr.go
index abfebae85c39..8b4a0ffba59a 100644
--- a/internal/shader/expr.go
+++ b/internal/shader/expr.go
@@ -913,7 +913,7 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 		var stmts []shaderir.Stmt
 
 		// Parse the index first
-		exprs, _, ss, ok := cs.parseExpr(block, fname, e.Index, markLocalVariableUsed)
+		exprs, _, ss, ok := cs.parseExpr(block, fname, e.Index, true)
 		if !ok {
 			return nil, nil, nil, false
 		}
diff --git a/internal/shader/syntax_test.go b/internal/shader/syntax_test.go
index e57dab97e998..fae66988031d 100644
--- a/internal/shader/syntax_test.go
+++ b/internal/shader/syntax_test.go
@@ -514,6 +514,21 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 `)); err == nil {
 		t.Errorf("error must be non-nil but was nil")
 	}
+
+	// Issue #2848
+	if _, err := compileToIR([]byte(`package main
+
+func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
+	var floats [4]float
+	for i := 0; i < 3; i++ {
+		j := i + 1
+		floats[j] = float(i)
+	}
+	return vec4(floats[0], floats[1], floats[2], floats[3])
+}
+`)); err != nil {
+		t.Error(err)
+	}
 }
 
 func TestSyntaxBlankLhs(t *testing.T) {