(#11627) linter - check ConanFile import and cross_building

* linter - check ConanFile import and cross_building

* remove unused code

* Add docs

* improve docs

* example - abseil

* md syntax

* revert uneeded changes

* Update docs/v2_linter.md

Co-authored-by: Daniel <danimanzaneque@gmail.com>

Co-authored-by: Daniel <danimanzaneque@gmail.com>

docs/v2_linter.md

@@ -0,0 +1,44 @@
+Linter to help migration to Conan v2
+====================================
+
+On our [path to Conan v2](v2_roadmap.md) we are leveraging on custom Pylint rules. This
+linter will run for every pull-request that is submitted to the repository and will
+raise some warnings and errors that should be addressed in order to migrate the
+recipes to Conan v2.
+
+It is important to note that these rules are targetting Conan v2 compatibility layer, their
+purpose is to fail for v1 syntax that will be no longer available in v2. Even if the syntax
+if perfectly valid in Conan v1, the recipe might fail here because it is not v2-compliant.
+
+> **Note.-** Some of the errored checks might be just plain Python syntax errors, while
+> others might be related to the custom rules added by us.
+
+Here you can find some examples of the extra rules we are adding:
+
+## Import ConanFile from `conan`
+
+The module `conans` is deprecated in Conan v2. Now all the imports should be done from
+module `conan`:
+
+```python
+from conan import ConanFile
+```
+
+## Import tools from `conan`
+
+All v2-compatible tools are available in module `conan.tools` under different submodules. Recipes
+should start to import their tools from this new module. Some of the new tools accept new 
+argument, please, check the [Conan documentation](https://docs.conan.io/en/latest/reference/conanfile/tools.html).
+
+For example, the `cross_building` tool now should be used like:
+
+```python
+from conan.tools.build import cross_building
+
+...
+class Recipe(ConanFile):
+
+    def test(self):
+        if not cross_building(self):
+            pass
+```

docs/v2_migration.md

@@ -6,6 +6,8 @@
 > will be taken in ConanCenter and this repository to start running
 > Conan v2 in pull requests.
 
+> ⚠️  Read about the [linter in pull requests](v2_linter.md).
+
 It's time to start thinking seriously about Conan v2 and prepare recipes
 for the incoming changes. Conan v2 comes with many
 changes and improvements, you can read about them in the

linter/check_import_conanfile.py

@@ -0,0 +1,28 @@
+
+from pylint.checkers import BaseChecker
+from pylint.interfaces import IAstroidChecker
+from astroid import nodes, Const, AssignName
+
+
+class ImportConanFile(BaseChecker):
+    """
+       Import ConanFile from new 'conan' module
+    """
+
+    __implements__ = IAstroidChecker
+
+    name = "conan-import-conanfile"
+    msgs = {
+        "W9006": (
+            "Import ConanFile from new module: `from conan import ConanFile`. Old import is deprecated in Conan v2.",
+            "conan-import-conanfile",
+            "Import ConanFile from new module: `from conan import ConanFile`. Old import is deprecated in Conan v2.",
+        ),
+    }
+
+    def visit_importfrom(self, node: nodes.ImportFrom) -> None:
+        basename = node.modname
+        if basename == 'conans':
+            names = [name for name, _ in node.names]
+            if 'ConanFile' in names:
+                self.add_message("conan-import-conanfile", node=node)

linter/conanv2_transition.py

@@ -1,7 +1,9 @@
 """Pylint plugin for Conan Center Index"""
 from pylint.lint import PyLinter
-from linter.package_name import PackageName
+from linter.check_package_name import PackageName
+from linter.check_import_conanfile import ImportConanFile
 
 
 def register(linter: PyLinter) -> None:
     linter.register_checker(PackageName(linter))
+    linter.register_checker(ImportConanFile(linter))

linter/pylintrc_recipe

@@ -1,6 +1,8 @@
 [MASTER]
 load-plugins=linter.conanv2_transition,
-             linter.conanfile_transform
+             linter.transform_conanfile,
+             linter.transform_imports
+
 py-version=3.6
 recursive=no
 suggestion-mode=yes
@@ -17,7 +19,8 @@ disable=fixme,
         import-outside-toplevel  # TODO: Remove
 
 enable=conan-bad-name,
-       conan-missing-name
+       conan-missing-name,
+       conan-import-conanfile
 
 [REPORTS]
 evaluation=max(0, 0 if fatal else 10.0 - ((float(5 * error) / statement) * 10))

linter/pylintrc_testpackage

@@ -1,6 +1,7 @@
 [MASTER]
 load-plugins=linter.conanv2_transition,
-             linter.conanfile_transform
+             linter.transform_conanfile,
+             linter.transform_imports
 py-version=3.6
 recursive=no
 suggestion-mode=yes

linter/transform_imports.py

@@ -0,0 +1,25 @@
+
+import astroid
+from pylint.lint import PyLinter
+
+"""
+Here we are transforming the imports to mimic future Conan v2 release. With
+these changes, built-in checks in Pylint will raise with different errors, so
+we are modifying the messages to point users in the right direction.
+"""
+
+
+def register(linter: PyLinter):
+    msge1101 = linter.msgs_store._messages_definitions["E1101"]
+    msge1101.msg += ". Please, check https://github.com/conan-io/conan-center-index/blob/master/docs/v2_linter.md"
+    linter.msgs_store.register_message(msge1101)
+
+def transform_tools(module):
+    """ Transform import module """
+    if 'cross_building' in module.locals:
+        del module.locals['cross_building']
+
+
+astroid.MANAGER.register_transform(
+    astroid.Module, transform_tools,
+    lambda node: node.qname() == "conans.tools")