Warn on empty version ranges (#17405)

* Warn on empty version ranges

* Better message

* Move message to a better place

conan/cli/printers/graph.py

@@ -68,6 +68,10 @@ def _format_resolved(title, reqs_to_print):
                        "it might be removed in 3.0.")
         output.warning("Consider using version-ranges instead.")
     _format_resolved("Resolved version ranges", graph.resolved_ranges)
+    for req in graph.resolved_ranges:
+        if str(req.version) == "[]":
+            output.warning("Empty version range usage is discouraged. Use [*] instead", warn_tag="deprecated")
+            break
 
     overrides = graph.overrides()
     if overrides:

test/integration/graph/core/test_version_ranges.py

@@ -437,3 +437,13 @@ def test_bad_options_syntax(version_range, should_warn):
         assert "its presence unconditionally enables prereleases" in tc.out
     else:
         assert "its presence unconditionally enables prereleases" not in tc.out
+
+
+def test_empty_version_ranger():
+    tc = TestClient(light=True)
+    tc.save({"lib/conanfile.py": GenConanfile("lib", "1.0"),
+             "app/conanfile.py": GenConanfile("app", "1.0").with_requires("lib/[]")})
+    tc.run("export lib")
+    tc.run("graph info app")
+    assert "lib/[]: lib/1.0" in tc.out
+    assert "Empty version range usage is discouraged" in tc.out

test/unittests/model/version/test_version_range.py

@@ -112,6 +112,10 @@ def test_range(version_range, conditions, versions_in, versions_out):
     ['>1 <=2.0', False, ["1.1", "1.9", "2.0"], ["0.9", "1.0-pre.1", "1.0", "1.1-pre.1", "2.0-pre"]],
     # This should be old and new behaviors remain the same
     ['>1 <=2.0', True, ["1.1-pre.1", "1.1", "1.9", "2.0", "2.0-pre"], ["0.9", "1.0", "1.0-pre.1"]],
+
+    # Codified quirks
+    ['', False, ["1.0", "2.0"], ["1.0-pre.1", "2.0-pre.1"]],
+    ['', True, ["1.0", "2.0", "1.0-pre.1", "2.0-pre.1"], []],
 ])
 def test_range_prereleases_conf(version_range, resolve_prereleases, versions_in, versions_out):
     r = VersionRange(version_range)