build_requires visible can be overriden

conans/client/graph/graph_builder.py

@@ -232,6 +232,17 @@ def _resolved_system_tool(node, require, profile_build, profile_host, resolve_pr
                             return d, ConanFile(str(d)), RECIPE_SYSTEM_TOOL, None
 
     def _create_new_node(self, node, require, graph, profile_host, profile_build, graph_lock):
+        if require.ref.version == "<host_version>":
+            if not require.build or require.visible:
+                raise ConanException(f"{node.ref} require '{require.ref}': 'host_version' can only "
+                                     "be used for non-visible tool_requires")
+            req = Requirement(require.ref, headers=True, libs=True, visible=True)
+            transitive = node.transitive_deps.get(req)
+            if transitive is None:
+                raise ConanException(f"{node.ref} require '{require.ref}': didn't find a matching "
+                                     "host dependency")
+            require.ref.version = transitive.require.ref.version
+
         if graph_lock is not None:
             # Here is when the ranges and revisions are resolved
             graph_lock.resolve_locked(node, require, self._resolve_prereleases)

conans/model/requires.py

@@ -392,10 +392,11 @@ class BuildRequirements:
     def __init__(self, requires):
         self._requires = requires
 
-    def __call__(self, ref, package_id_mode=None, visible=False, run=None, options=None):
+    def __call__(self, ref, package_id_mode=None, visible=False, run=None, options=None,
+                 override=None):
         # TODO: Check which arguments could be user-defined
         self._requires.build_require(ref, package_id_mode=package_id_mode, visible=visible, run=run,
-                                     options=options)
+                                     options=options, override=override)
 
 
 class ToolRequirements:
@@ -485,7 +486,7 @@ def __call__(self, str_ref, **kwargs):
         self._requires[req] = req
 
     def build_require(self, ref, raise_if_duplicated=True, package_id_mode=None, visible=False,
-                      run=None, options=None):
+                      run=None, options=None, override=None):
         """
              Represent a generic build require, could be a tool, like "cmake" or a bundle of build
              scripts.
@@ -501,7 +502,7 @@ def build_require(self, ref, raise_if_duplicated=True, package_id_mode=None, vis
         # FIXME: This raise_if_duplicated is ugly, possibly remove
         ref = RecipeReference.loads(ref)
         req = Requirement(ref, headers=False, libs=False, build=True, run=run, visible=visible,
-                          package_id_mode=package_id_mode, options=options)
+                          package_id_mode=package_id_mode, options=options, override=override)
 
         if raise_if_duplicated and self._requires.get(req):
             raise ConanException("Duplicated requirement: {}".format(ref))

conans/test/integration/build_requires/build_requires_test.py

@@ -1,3 +1,4 @@
+import json
 import os
 import platform
 import textwrap
@@ -747,3 +748,148 @@ def requirements(self):
     c.assert_listed_require({"dep/1.0": "Cache"})
     c.run("create consumer --build-require")
     assert "dep/1.0" not in c.out
+
+
+class TestBuildTrackHost:
+
+    def test_overriden_host_but_not_build(self):
+        """
+        Making the ``tool_requires(..., visible=True)`` works, and allows overriding, but
+        propagates the build-requirement to protobuf/protoc down the graph, and VirtualBuildEnv
+        will put ``protoc`` from it in the PATH. Not a problem in majority of cases, but not the
+        cleanest
+        """
+        c = TestClient()
+        pkg = textwrap.dedent("""
+            from conan import ConanFile
+            class ProtoBuf(ConanFile):
+                name = "pkg"
+                version = "0.1"
+                def requirements(self):
+                    self.requires("protobuf/1.0")
+                def build_requirements(self):
+                    self.tool_requires("protobuf/1.0", visible=True)
+            """)
+        c.save({"protobuf/conanfile.py": GenConanfile("protobuf"),
+                "pkg/conanfile.py": pkg,
+                "app/conanfile.py": GenConanfile().with_requires("pkg/0.1")
+                                                  .with_requirement("protobuf/1.1", override=True)
+                                                  .with_build_requirement("protobuf/1.1",
+                                                                          override=True)})
+        c.run("create protobuf --version=1.0")
+        c.run("create protobuf --version=1.1")
+        c.run("create pkg")
+        c.run("install app")
+        c.assert_listed_require({"protobuf/1.1": "Cache"})
+        c.assert_listed_require({"protobuf/1.1": "Cache"}, build=True)
+
+    def test_overriden_host_version(self):
+        """
+        Make the tool_requires follow the regular require with the expression "<host_version>"
+        """
+        c = TestClient()
+        pkg = textwrap.dedent("""
+            from conan import ConanFile
+            class ProtoBuf(ConanFile):
+                name = "pkg"
+                version = "0.1"
+                def requirements(self):
+                    self.requires("protobuf/1.0")
+                def build_requirements(self):
+                    self.tool_requires("protobuf/<host_version>")
+            """)
+        c.save({"protobuf/conanfile.py": GenConanfile("protobuf"),
+                "pkg/conanfile.py": pkg,
+                "app/conanfile.py": GenConanfile().with_requires("pkg/0.1")
+                                                  .with_requirement("protobuf/1.1", override=True)})
+        c.run("create protobuf --version=1.0")
+        c.run("create protobuf --version=1.1")
+        c.run("create pkg")
+        c.run("install pkg")  # make sure it doesn't crash
+        c.run("install app")
+        c.assert_listed_require({"protobuf/1.1": "Cache"})
+        c.assert_listed_require({"protobuf/1.1": "Cache"}, build=True)
+        # verify locks work
+        c.run("lock create app")
+        lock = json.loads(c.load("app/conan.lock"))
+        build_requires = lock["build_requires"]
+        assert len(build_requires) == 1
+        assert "protobuf/1.1" in build_requires[0]
+        # lock can be used
+        c.run("install app --lockfile=app/conan.lock")
+        c.assert_listed_require({"protobuf/1.1": "Cache"}, build=True)
+
+    def test_overriden_host_version_version_range(self):
+        """
+        same as above, but using version ranges instead of overrides
+        """
+        c = TestClient()
+        pkg = textwrap.dedent("""
+            from conan import ConanFile
+            class ProtoBuf(ConanFile):
+                name = "pkg"
+                version = "0.1"
+                def requirements(self):
+                    self.requires("protobuf/[*]")
+                def build_requirements(self):
+                    self.tool_requires("protobuf/<host_version>")
+            """)
+        c.save({"protobuf/conanfile.py": GenConanfile("protobuf"),
+                "pkg/conanfile.py": pkg,
+                "app/conanfile.py": GenConanfile().with_requires("pkg/0.1")})
+        c.run("create protobuf --version=1.0")
+        c.run("create pkg")
+        c.run("install pkg")  # make sure it doesn't crash
+        c.run("install app")
+        c.assert_listed_require({"protobuf/1.0": "Cache"})
+        c.assert_listed_require({"protobuf/1.0": "Cache"}, build=True)
+
+        c.run("create protobuf --version=1.1")
+        c.run("install pkg")  # make sure it doesn't crash
+        c.run("install app")
+        c.assert_listed_require({"protobuf/1.1": "Cache"})
+        c.assert_listed_require({"protobuf/1.1": "Cache"}, build=True)
+        # verify locks work
+        c.run("lock create app")
+        lock = json.loads(c.load("app/conan.lock"))
+        build_requires = lock["build_requires"]
+        assert len(build_requires) == 1
+        assert "protobuf/1.1" in build_requires[0]
+        # lock can be used
+        c.run("install app --lockfile=app/conan.lock")
+        c.assert_listed_require({"protobuf/1.1": "Cache"}, build=True)
+
+    def test_track_host_error_nothost(self):
+        """
+        if no host requirement is defined, it will be an error
+        """
+        c = TestClient()
+        pkg = textwrap.dedent("""
+            from conan import ConanFile
+            class ProtoBuf(ConanFile):
+                name = "protobuf"
+                def build_requirements(self):
+                    self.tool_requires("protobuf/<host_version>")
+            """)
+
+        c.save({"pkg/conanfile.py": pkg})
+        c.run("install pkg", assert_error=True)
+        assert "ERROR: protobuf/None require 'protobuf/<host_version>': " \
+               "didn't find a matching host dependency" in c.out
+
+    def test_track_host_errors_trait(self):
+        """
+        It is not possible to make host_version visible too
+        """
+        c = TestClient()
+        pkg = textwrap.dedent("""
+            from conan import ConanFile
+            class ProtoBuf(ConanFile):
+                name = "protobuf"
+                def requirements(self):
+                   self.tool_requires("other/<host_version>", visible=True)
+            """)
+        c.save({"pkg/conanfile.py": pkg})
+        c.run("install pkg", assert_error=True)
+        assert "ERROR: protobuf/None require 'other/<host_version>': 'host_version' " \
+               "can only be used for non-visible tool_requires" in c.out