[POC] Selectively override compat entries

src/Registry/registry_instance.jl

@@ -165,9 +165,42 @@ function init_package_info!(pkg::PkgEntry)
 
     @init! pkg.info = PkgInfo(repo, subdir, version_info, compat, deps)
 
+    override_compat!(pkg)
+
     return pkg.info
 end
 
+function override_compat!(pkg::PkgEntry)
+    filename = compat_override_filename()
+    if isfile(filename)
+        @info "Using compat override file at \"$(filename)\"" maxlog = 1
+        @warn "You are using the compat override feature. Use of this feature may cause packages to break. It is the responsibility of the user (not the maintainers of any packages) to solve any problems that arise from the use of this feature." maxlog = 1
+        all_overrides = TOML.parsefile(filename)
+        if haskey(all_overrides, string(pkg.uuid))
+            pkg_override = all_overrides[string(pkg.uuid)]
+            initialize_uncompressed!(pkg.info)
+            version_info = pkg.info.version_info
+            for version_number in keys(version_info)
+                version_number_info = version_info[version_number]
+                if haskey(pkg_override, string(version_number))
+                    override = pkg_override[string(version_number)]
+                    uncompressed_compat = version_number_info.uncompressed_compat
+                    for uuid in keys(uncompressed_compat)
+                        if haskey(override, string(uuid))
+                            new_compat = Pkg.Types.semver_spec(override[string(uuid)])
+                            uncompressed_compat[uuid] = new_compat
+                        end
+                    end
+                end
+            end
+        end
+    end
+    return pkg
+end
+
+function compat_override_filename()
+    return joinpath(homedir(), ".julia", "config", "compat-overrides.toml")
+end
 
 struct RegistryInstance
     path::String