Derive conanfile.version from latest available in conandata.yml as last alternative

conan/internal/loader.py

@@ -16,6 +16,7 @@
 from conan.tools.cmake import cmake_layout
 from conan.tools.google import bazel_layout
 from conan.tools.microsoft import vs_layout
+from conan.tools.scm import Version
 from conan.internal.errors import conanfile_exception_formatter, NotFoundException
 from conan.errors import ConanException
 from conan.internal.model.conan_file import ConanFile
@@ -143,6 +144,16 @@ def load_named(self, conanfile_path, name, version, user, channel, graph_lock=No
             with conanfile_exception_formatter("conanfile.py", "set_version"):
                 conanfile.set_version()
 
+        if not conanfile.version:
+            # Last chance, try to get version from conan_data.
+            # Only works if only one version is present
+            conan_data = getattr(conanfile, "conan_data", {})
+            sources = conan_data.get("sources", {}) if conan_data else {}
+            sources = sources or {}
+            sorted_versions = sorted(sources.keys(), key=lambda x: Version(x))
+            if sorted_versions:
+                conanfile.version = sorted_versions.pop()
+
         return conanfile
 
     def load_export(self, conanfile_path, name, version, user, channel, graph_lock=None,

test/integration/conanfile/conan_data_test.py

@@ -483,3 +483,62 @@ def generate(self):
           '2.0':
             x: foo
         """)
+
+
+@pytest.mark.parametrize("command", [
+    "source",
+    "graph info",
+    "create",
+    "export"
+])
+def test_commands_auto_pick_version(command):
+    c = TestClient(light=True)
+    conanfile = textwrap.dedent("""
+        from conan import ConanFile
+        class Pkg(ConanFile):
+            name = "pkg"
+
+            def source(self):
+                self.output.info("ok")
+        """)
+    conandata = textwrap.dedent("""
+        sources:
+            1.0:
+                url: "url1"
+            2.0:
+                url: "url2"
+    """)
+
+    c.save({"conanfile.py": conanfile,
+            "conandata.yml": conandata})
+    c.run(command)
+    assert "pkg/2.0" in c.out
+
+
+@pytest.mark.parametrize("conandata", [
+    pytest.param(
+        textwrap.dedent("""
+        sources:
+            # Empty, no content
+        """), id="empty sources"),
+    pytest.param(
+        textwrap.dedent("""
+        # No sources key
+        foo: 1
+        """), id="no sources"),
+])
+def test_commands_auto_pick_version_no_version_conandata(conandata):
+    c = TestClient(light=True)
+    conanfile = textwrap.dedent("""
+            from conan import ConanFile
+            class Pkg(ConanFile):
+                name = "pkg"
+
+                def source(self):
+                    self.output.info("ok")
+            """)
+
+    c.save({"conanfile.py": conanfile,
+            "conandata.yml": conandata})
+    c.run("create", assert_error=True)
+    assert "conanfile didn't specify version" in c.out