internal/shader: bug fix: forbid duplicated uniform variables

Closes #2648

internal/shader/shader.go

@@ -407,6 +407,12 @@ func (cs *compileState) parseDecl(b *block, fname string, d ast.Decl) ([]shaderi
 								cs.addError(s.Names[i].Pos(), fmt.Sprintf("global variables must be exposed: %s", v.name))
 							}
 						}
+						for _, name := range cs.ir.UniformNames {
+							if name == v.name {
+								cs.addError(s.Pos(), fmt.Sprintf("%s redeclared in this block", name))
+								return nil, false
+							}
+						}
 						cs.ir.UniformNames = append(cs.ir.UniformNames, v.name)
 						cs.ir.Uniforms = append(cs.ir.Uniforms, v.typ)
 					}

internal/shader/syntax_test.go

@@ -3543,3 +3543,46 @@ func foo() {
 		t.Error("compileToIR must return an error but did not")
 	}
 }
+
+// Issue #2648
+func TestDuplicatedVariables(t *testing.T) {
+	if _, err := compileToIR([]byte(`package main
+
+var Foo int
+var Foo int
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+	if _, err := compileToIR([]byte(`package main
+
+var Foo int
+var Bar float
+var Foo vec2
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+	if _, err := compileToIR([]byte(`package main
+
+func foo() {
+	var x int
+	var x int
+	_ = x
+}
+
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+	if _, err := compileToIR([]byte(`package main
+
+func foo() {
+	var x int
+	var y float
+	var x vec2
+	_ = x
+	_ = y
+}
+
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+}