internal/shader: bug fix: return true for float must fail

Closes #2706

internal/shader/stmt.go

@@ -500,12 +500,22 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 			}
 			if expr.Const != nil {
 				switch outT.Main {
+				case shaderir.Bool:
+					if expr.Const.Kind() != gconstant.Bool {
+						cs.addError(stmt.Pos(), fmt.Sprintf("cannot use type %s as type %s in return argument", t.String(), &outT))
+						return nil, false
+					}
+					t = shaderir.Type{Main: shaderir.Bool}
 				case shaderir.Int:
 					if !cs.forceToInt(stmt, &expr) {
 						return nil, false
 					}
 					t = shaderir.Type{Main: shaderir.Int}
 				case shaderir.Float:
+					if gconstant.ToFloat(expr.Const).Kind() == gconstant.Unknown {
+						cs.addError(stmt.Pos(), fmt.Sprintf("cannot use type %s as type %s in return argument", t.String(), &outT))
+						return nil, false
+					}
 					t = shaderir.Type{Main: shaderir.Float}
 				}
 			}

internal/shader/syntax_test.go

@@ -3249,3 +3249,45 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		t.Error(err)
 	}
 }
+
+// Issue #2706
+func TestSyntaxReturnConst(t *testing.T) {
+	cases := []struct {
+		typ  string
+		stmt string
+		err  bool
+	}{
+		{typ: "bool", stmt: "true", err: false},
+		{typ: "int", stmt: "true", err: true},
+		{typ: "float", stmt: "true", err: true},
+		{typ: "bool", stmt: "1", err: true},
+		{typ: "int", stmt: "1", err: false},
+		{typ: "float", stmt: "1", err: false},
+		{typ: "bool", stmt: "1.0", err: true},
+		{typ: "int", stmt: "1.0", err: false},
+		{typ: "float", stmt: "1.0", err: false},
+		{typ: "bool", stmt: "1.1", err: true},
+		{typ: "int", stmt: "1.1", err: true},
+		{typ: "float", stmt: "1.1", err: false},
+	}
+
+	for _, c := range cases {
+		typ := c.typ
+		stmt := c.stmt
+		src := fmt.Sprintf(`package main
+
+func Foo() %s {
+	return %s
+}
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return position
+}`, typ, stmt)
+		_, err := compileToIR([]byte(src))
+		if err == nil && c.err {
+			t.Errorf("return %s for type %s must return an error but does not", stmt, typ)
+		} else if err != nil && !c.err {
+			t.Errorf("return %s for type %s must not return nil but returned %v", stmt, typ, err)
+		}
+	}
+}