# Unexpected behavior of the GENERATED source file property and CMP0118

**URL:** https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821
**Category:** Development
**Created:** [July 23, 2021, 10:57am UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821 "2021-07-23T10:57:53Z")
**Posts on this page:** 5
**Page:** 1

<div class="post-metadata">

### Author: ![petwu](https://discourse.cmake.org/user_avatar/discourse.cmake.org/petwu/32/1399_2.png) [@petwu](https://discourse.cmake.org/u/petwu)
#### Post date: [July 23, 2021, 10:57am UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821/1 "2021-07-23T10:57:53Z")

</div>

The policy [CMP0118](https://cmake.org/cmake/help/v3.21/policy/CMP0118.html) states that the [GENERATED](https://cmake.org/cmake/help/v3.21/prop_sf/GENERATED.html) source file property is now visible in all directory scopes, not just the one it was set in. Now consider the following minimal example:

```cmake
# CMP0118/CMakeLists.txt
cmake_minimum_required(VERSION 3.21)
project(CMP0118 LANGUAGES NONE)
set(_test_file "${CMAKE_BINARY_DIR}/subdir/test.txt")
add_subdirectory(subdir)
get_source_file_property(_generated "${_test_file}" GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")
get_property(_generated SOURCE "${_test_file}" PROPERTY GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")
get_source_file_property(_generated "${_test_file}" DIRECTORY subdir GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")
get_property(_generated SOURCE "${_test_file}" DIRECTORY subdir PROPERTY GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")

# CMP0118/subdir/CMakeLists.txt
add_custom_command(
  OUTPUT "${_test_file}"
  COMMAND ${CMAKE_COMMAND} -E touch "${_test_file}"
  COMMENT "Generating ${_test_file}"
)
add_custom_target(test ALL DEPENDS "${_test_file}")
get_source_file_property(_generated "${_test_file}" GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")
get_property(_generated SOURCE "${_test_file}" PROPERTY GENERATED)
message(STATUS "[${CMAKE_CURRENT_SOURCE_DIR}] GENERATED = ${_generated}")

```

When I run this, I get this output:

```plaintext
-- [C:/.../CMP0118/subdir] GENERATED = 1
-- [C:/.../CMP0118/subdir] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = NOTFOUND
-- [C:/.../CMP0118] GENERATED = 0
-- [C:/.../CMP0118] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = 1

```

What I expected:

```plaintext
-- [C:/.../CMP0118/subdir] GENERATED = 1
-- [C:/.../CMP0118/subdir] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = 1
-- [C:/.../CMP0118] GENERATED = 1

```

I expected this, because the documentation says thinks like the `GENERATED` property was “visible in all directories”, “globally visible” or “can be set and retrieved from any directory scope”. I did not at all expect that I had to use the `DIRECTORY` option of `get[_source_file]_property()` to specify the scope in order to read a “globally visible” property. So either this is a bug and the `GENERATED` property should actually be retrievable the way I read the documentation (from any scope; without specifying the `DIRECTORY`) or the documentation could be much more clear about this.

Also, I think the documentation of CMP0118 has a small mistake:

> Unlike many policies, CMake version 3.21.0 does _not_ warn when this policy is not set and simply uses `OLD` behavior with regard to visibility of the `GENERATED` property.

It should say that the `NEW` behavior is the default, not the `OLD` one, right? I checked with `cmake_policy(GET CMP0118)` and it returned `NEW` as expected.

---

<div class="post-metadata">

### Author: ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [July 23, 2021, 11:58am UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821/2 "2021-07-23T11:58:46Z")

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> [@petwu](#):
>
> It should say that the `NEW` behavior is the default, not the `OLD` one, right? I checked with `cmake_policy(GET CMP0118)` and it returned `NEW` as expected.

No, the `NEW` behavior is “the default” in your case because you said your minimum version is 3.21 and that declares that you are not relying upon any behaviors specific to older versions.

That said, I’m not familiar with this policy, so those questions are for someone else. @dbahadir?

---

<div class="post-metadata">

### Author: ![petwu](https://discourse.cmake.org/user_avatar/discourse.cmake.org/petwu/32/1399_2.png) [@petwu](https://discourse.cmake.org/u/petwu)
#### Post date: [July 23, 2021, 12:21pm UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821/3 "2021-07-23T12:21:55Z")

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> [@ben.boeckel](#):
>
> No, the `NEW` behavior is “the default” in your case because you said your minimum version is 3.21 and that declares that you are not relying upon any behaviors specific to older versions.

I get that the minimum version of 3.21 is the reason why the policy is set to `NEW`. But since we apparently read that sentence in different ways, I’m going to explain my point further.

The sentence before states: “Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly”. So the “when this policy is not set” sounds like “if not set _explicitly_ with `cmake_policy()` CMake 3.21 uses the `OLD` behavior”.

So maybe it is just written confusingly and should say “[…] does _not_ warn then this policy is not enabled (set to `OLD` explicity) and simplay uses the `OLD` behavior […]” or something similar.

---

<div class="post-metadata">

### Author: ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [July 23, 2021, 12:49pm UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821/4 "2021-07-23T12:49:19Z")

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The documentation for [`cmake_minimum_required`](https://cmake.org/cmake/help/latest/command/cmake_minimum_required.html) describes how it sets up policies. I suppose the documentation in each policy could be clearer.

---

<div class="post-metadata">

### Author: ![craig.scott](https://discourse.cmake.org/user_avatar/discourse.cmake.org/craig.scott/32/20_2.png) [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [September 7, 2021, 1:19am UTC](https://discourse.cmake.org/t/unexpected-behavior-of-the-generated-source-file-property-and-cmp0118/3821/5 "2021-09-07T01:19:24Z")

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Also see [Behavior of where CMP0118's value is used is ambiguous](https://discourse.cmake.org/t/behavior-of-where-cmp0118s-value-is-used-is-ambiguous/4045) for further problems with the `GENERATED` property and policy CMP0118.