bzlmod: Fix interaction between replace and implicit upgrade check (#…

…1492)

Ensures that implicit version upgrade warnings are not emitted for the
root module if it uses replace directives to update versions.

internal/bzlmod/go_deps.bzl

@@ -245,26 +245,34 @@ def _go_deps_impl(module_ctx):
         fail("Some gazelle_overrides did not target a Go module with a matching path: {}"
             .format(", ".join(unmatched_gazelle_overrides)))
 
-    for path, root_version in root_versions.items():
-        if semver.to_comparable(root_version) < module_resolutions[path].version:
-            outdated_direct_dep_printer(
-                "For Go module \"{path}\", the root module requires module version v{root_version}, but got v{resolved_version} in the resolved dependency graph.".format(
-                    path = path,
-                    root_version = root_version,
-                    resolved_version = module_resolutions[path].raw_version,
-                ),
-            )
-
     # All `replace` directives are applied after version resolution.
     # We can simply do this by checking the replace paths' existence
     # in the module resolutions and swapping out the entry.
     for path, replace in replace_map.items():
         if path in module_resolutions:
+            new_version = semver.to_comparable(replace.version)
             module_resolutions[path] = with_replaced_or_new_fields(module_resolutions[path],
                 replace = replace.to_path,
-                version = semver.to_comparable(replace.version),
+                version = new_version,
                 raw_version = replace.version,
             )
+            if path in root_versions:
+                if replace != replace.to_path:
+                    # If the root module replaces a Go module with a completely different one, do
+                    # not ever report an implicit version upgrade.
+                    root_versions.pop(path)
+                else:
+                    root_versions[path] = new_version
+
+    for path, root_version in root_versions.items():
+        if semver.to_comparable(root_version) < module_resolutions[path].version:
+            outdated_direct_dep_printer(
+                "For Go module \"{path}\", the root module requires module version v{root_version}, but got v{resolved_version} in the resolved dependency graph.".format(
+                    path = path,
+                    root_version = root_version,
+                    resolved_version = module_resolutions[path].raw_version,
+                ),
+            )
 
     for path, module in module_resolutions.items():
         go_repository(