internal/shader: bug fix: wrong for-loop should fail compilation

Closes #2680

internal/shader/stmt.go

@@ -214,7 +214,7 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 		}
 
 		// Create a new pseudo block for the initial statement, so that the counter variable belongs to the
-		// new pseudo block for each for-loop. Without this, the samely named counter variables in different
+		// new pseudo block for each for-loop. Without this, the same-named counter variables in different
 		// for-loops confuses the parser.
 		pseudoBlock, ok := cs.parseBlock(block, fname, []ast.Stmt{stmt.Init}, inParams, outParams, returnType, false)
 		if !ok {
@@ -240,6 +240,11 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 			return nil, false
 		}
 
+		if len(pseudoBlock.vars) != 1 {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+
 		vartype := pseudoBlock.vars[0].typ
 		init := ss[0].Exprs[1].Const
 

internal/shader/syntax_test.go

@@ -3521,3 +3521,25 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #2680
+func TestForWithLocalVariable(t *testing.T) {
+	if _, err := compileToIR([]byte(`package main
+
+func foo() {
+	i := 0
+	for i = 0; i < 1; i++ {
+	}
+}`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+	if _, err := compileToIR([]byte(`package main
+
+func foo() {
+	for i, j := 0, 0; i < 1; i++ {
+		_ = j
+	}
+}`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+}