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DOCS: Add an example of cmake_build_modules property to migration guide #9347

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Feb 14, 2022
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DOCS: Add an example of cmake_build_modules property to migration guide #9347

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68 changes: 52 additions & 16 deletions docs/preparing_recipes_for_conan2.md
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ properties model work, please check the [Conan documentation](https://docs.conan
### Update required_conan_version to ">=1.43.0"

If you set the property ``cmake_target_name`` in the recipe, the Conan minimum
required version should be updated to 1.43.
required version should be updated to 1.43.

```python

Expand Down Expand Up @@ -82,7 +82,7 @@ take into account:
* The value of the ``.names`` attribute value in recipes is just a part of the final
target name for CMake generators. Conan will complete the rest of the target name by
pre-pending a namespace (with ``::`` separator) to the ``.names`` value. This namespace takes
the same value as the ``.names`` value. Let's see an example:
the same value as the ``.names`` value. Let's see an example:

```python
class SomePkgConan(ConanFile):
Expand All @@ -99,7 +99,7 @@ This recipe generates the target ``some-pkg::some-pkg`` for both the
remember that if no ``.names`` attribute were set, Conan would create the target
``somepkg::somepkg`` for both generators by default.

As we explained before, the ``cmake_target_name`` sets the **complete target name**, so,
As we explained before, the ``cmake_target_name`` sets the **complete target name**, so,
to translate this information to the new model we should add the following lines:

```python
Expand All @@ -110,7 +110,7 @@ class SomePkgConan(ConanFile):
self.cpp_info.names["cmake_find_package"] = "some-pkg"
self.cpp_info.names["cmake_find_package_multi"] = "some-pkg"
# CMakeDeps does NOT add any namespace automatically
self.cpp_info.set_property("cmake_target_name", "some-pkg::some-pkg")
self.cpp_info.set_property("cmake_target_name", "some-pkg::some-pkg")
...
```

Expand All @@ -126,11 +126,11 @@ class SomePkgConan(ConanFile):
...
def package_info(self):
# These generators fallback the filenames for the .cmake files
# in the .names attribute value and generate
# in the .names attribute value and generate
self.cpp_info.names["cmake_find_package"] = "some-pkg" # generates module file Findsome-pkg.cmake
self.cpp_info.names["cmake_find_package_multi"] = "some-pkg" # generates config file some-pkg-config.cmake

self.cpp_info.set_property("cmake_target_name", "some-pkg::some-pkg")
self.cpp_info.set_property("cmake_target_name", "some-pkg::some-pkg")
self.cpp_info.set_property("cmake_file_name", "some-pkg") # generates config file some-pkg-config.cmake
...
```
Expand Down Expand Up @@ -171,17 +171,17 @@ class ExpatConan(ConanFile):

# creates EXPAT::EXPAT target for module files FindEXPAT.cmake
self.cpp_info.set_property("cmake_target_name", "EXPAT::EXPAT")
# creates expat::expat target for config files expat-config.cmake
self.cpp_info.set_property("cmake_module_target_name", "expat::expat")
# creates expat::expat target for config files expat-config.cmake
self.cpp_info.set_property("cmake_module_target_name", "expat::expat")

# generates module file FindEXPAT.cmake
self.cpp_info.set_property("cmake_file_name", "EXPAT")
self.cpp_info.set_property("cmake_file_name", "EXPAT")
# generates config file expat-config.cmake
self.cpp_info.set_property("cmake_module_file_name", "expat")
self.cpp_info.set_property("cmake_module_file_name", "expat")

# config is the default for CMakeDeps
# we set cmake_find_mode to both to generate both module and config files
self.cpp_info.set_property("cmake_find_mode", "both")
self.cpp_info.set_property("cmake_find_mode", "both")
...
```

Expand Down Expand Up @@ -230,7 +230,7 @@ class GlewConan(ConanFile):
self.cpp_info.set_property("cmake_module_file_name", "glew") # generates glew-config.cmake

# generate both modules and config files
self.cpp_info.set_property("cmake_find_mode", "both")
self.cpp_info.set_property("cmake_find_mode", "both")
...
```

Expand All @@ -255,7 +255,7 @@ class KtxConan(ConanFile):

def package_info(self):
# changes namespace to KTX::
self.cpp_info.names["cmake_find_package"] = "KTX"
self.cpp_info.names["cmake_find_package"] = "KTX"
...
# the target inherits the KTX:: namespace and sets the target KTX::ktx
self.cpp_info.components["libktx"].names["cmake_find_package"] = "ktx"
Expand All @@ -282,7 +282,7 @@ class KtxConan(ConanFile):
...

def package_info(self):
self.cpp_info.names["cmake_find_package"] = "KTX"
self.cpp_info.names["cmake_find_package"] = "KTX"
...
# FIXME: Remove the libktx component in Conan 2.0, this is just needed for
# compatibility with current generators
Expand All @@ -302,11 +302,11 @@ class KtxConan(ConanFile):
```

* **Use build modules to create aliases with arbitray names for targets**. Similar to the
previous example, some recipes use a build module with an alias to set an arbitray
previous example, some recipes use a build module with an alias to set an arbitrary
target name. Let's see the example of the [tensorflow-lite
recipe](https://github.com/conan-io/conan-center-index/blob/03b24bf128cbf15d23ed988b8d8ca0c0ba87d307/recipes/tensorflow-lite/all/conanfile.py),
that uses this workaround to define a ``tensorflow::tensorflowlite`` target.

```python
class TensorflowLiteConan(ConanFile):
name = "tensorflow-lite"
Expand Down Expand Up @@ -342,6 +342,42 @@ class TensorflowLiteConan(ConanFile):
...
```


### Translating .build_modules to cmake_build_modules

Previously we saw that some recipes use a build module with an alias to set an arbitrary target name.
But sometimes the declared ".build_modules" come from the original package that declares useful CMake functions, variables
etc. We need to use the property `cmake_build_modules` to declare a list of cmake files instead of using `cpp_info.build_modules`:

```python
class PyBind11Conan(ConanFile):
name = "pybind11"
...

def package_info(self):
...
for generator in ["cmake_find_package", "cmake_find_package_multi"]:
self.cpp_info.components["main"].build_modules[generator].append(os.path.join("lib", "cmake", "pybind11", "pybind11Common.cmake"))
...

```

To translate this information to the new model we declare the `cmake_build_modules` property in the `root cpp_info` object:

```python
class PyBind11Conan(ConanFile):
name = "pybind11"
...

def package_info(self):
...
self.cpp_info.set_property("cmake_build_modules", [os.path.join("lib", "cmake", "pybind11", "pybind11Common.cmake")])
...

```



### PkgConfigDeps

The case of ``PkgConfigDeps`` is much more straight forward than the ``CMakeDeps`` case.
Expand Down