[rubygems/rubygems] Fix `--prefer-local` flag

The original implementation of this flag was too naive and all it did
was restricting gems to locally installed versions if there are any
local versions installed.

However, it should be much smarter. For example:

* It should fallback to remote versions if locally installed version
  don't satisfy the requirements.
* It should pick locally installed versions even for subdependencies not
  yet discovered.

This commit fixes both issues by using a smarter approach similar to how
we resolve prereleases:

* First resolve optimistically using only locally installed gems.
* If any conflicts are found, scan those conflicts, allow remote
  versions for the specific gems that run into conflicts, and
  re-resolve.

https://github.com/rubygems/rubygems/commit/607a3bf479

Co-authored-by: Gourav Khunger <gouravkhunger18@gmail.com>

4 files changed, 47 insertions, 24 deletions

diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index d2cab437a0..5471a72fdd 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -571,7 +571,7 @@ module Bundler
       @resolution_packages ||= begin
         last_resolve = converge_locked_specs
         remove_invalid_platforms!
-        packages = Resolver::Base.new(source_requirements, expanded_dependencies, last_resolve, @platforms, locked_specs: @originally_locked_specs, unlock: @gems_to_unlock, prerelease: gem_version_promoter.pre?)
+        packages = Resolver::Base.new(source_requirements, expanded_dependencies, last_resolve, @platforms, locked_specs: @originally_locked_specs, unlock: @gems_to_unlock, prerelease: gem_version_promoter.pre?, prefer_local: @prefer_local)
         packages = additional_base_requirements_to_prevent_downgrades(packages, last_resolve)
         packages = additional_base_requirements_to_force_updates(packages)
         packages
@@ -655,19 +655,6 @@ module Bundler
       sources.non_global_rubygems_sources.all?(&:dependency_api_available?) && !sources.aggregate_global_source?
     end
 
-    def pin_locally_available_names(source_requirements)
-      source_requirements.each_with_object({}) do |(name, original_source), new_source_requirements|
-        local_source = original_source.dup
-        local_source.local_only!
-
-        new_source_requirements[name] = if local_source.specs.search(name).any?
-          local_source
-        else
-          original_source
-        end
-      end
-    end
-
     def current_platform_locked?
       @platforms.any? do |bundle_platform|
         MatchPlatform.platforms_match?(bundle_platform, local_platform)
@@ -983,7 +970,6 @@ module Bundler
       # look for that gemspec (or its dependencies)
       source_requirements = if precompute_source_requirements_for_indirect_dependencies?
         all_requirements = source_map.all_requirements
-        all_requirements = pin_locally_available_names(all_requirements) if @prefer_local
         { default: default_source }.merge(all_requirements)
       else
         { default: Source::RubygemsAggregate.new(sources, source_map) }.merge(source_map.direct_requirements)
diff --git a/lib/bundler/resolver.rb b/lib/bundler/resolver.rb
index de324fbcf3..a38b6974f8 100644
--- a/lib/bundler/resolver.rb
+++ b/lib/bundler/resolver.rb
@@ -84,9 +84,9 @@ module Bundler
     rescue PubGrub::SolveFailure => e
       incompatibility = e.incompatibility
 
-      names_to_unlock, names_to_allow_prereleases_for, extended_explanation = find_names_to_relax(incompatibility)
+      names_to_unlock, names_to_allow_prereleases_for, names_to_allow_remote_specs_for, extended_explanation = find_names_to_relax(incompatibility)
 
-      names_to_relax = names_to_unlock + names_to_allow_prereleases_for
+      names_to_relax = names_to_unlock + names_to_allow_prereleases_for + names_to_allow_remote_specs_for
 
       if names_to_relax.any?
         if names_to_unlock.any?
@@ -101,6 +101,12 @@ module Bundler
           @base.include_prereleases(names_to_allow_prereleases_for)
         end
 
+        if names_to_allow_remote_specs_for.any?
+          Bundler.ui.debug "Found conflicts with local versions of #{names_to_allow_remote_specs_for.join(", ")}. Will retry considering remote versions...", true
+
+          @base.include_remote_specs(names_to_allow_remote_specs_for)
+        end
+
         root, logger = setup_solver
 
         Bundler.ui.debug "Retrying resolution...", true
@@ -120,6 +126,7 @@ module Bundler
     def find_names_to_relax(incompatibility)
       names_to_unlock = []
       names_to_allow_prereleases_for = []
+      names_to_allow_remote_specs_for = []
       extended_explanation = nil
 
       while incompatibility.conflict?
@@ -134,6 +141,8 @@ module Bundler
             names_to_unlock << name
           elsif package.ignores_prereleases? && @all_specs[name].any? {|s| s.version.prerelease? }
             names_to_allow_prereleases_for << name
+          elsif package.prefer_local? && @all_specs[name].any? {|s| !s.is_a?(StubSpecification) }
+            names_to_allow_remote_specs_for << name
           end
 
           no_versions_incompat = [cause.incompatibility, cause.satisfier].find {|incompat| incompat.cause.is_a?(PubGrub::Incompatibility::NoVersions) }
@@ -143,7 +152,7 @@ module Bundler
         end
       end
 
-      [names_to_unlock.uniq, names_to_allow_prereleases_for.uniq, extended_explanation]
+      [names_to_unlock.uniq, names_to_allow_prereleases_for.uniq, names_to_allow_remote_specs_for.uniq, extended_explanation]
     end
 
     def parse_dependency(package, dependency)
@@ -244,7 +253,7 @@ module Bundler
 
     def all_versions_for(package)
       name = package.name
-      results = (@base[name] + filter_prereleases(@all_specs[name], package)).uniq {|spec| [spec.version.hash, spec.platform] }
+      results = (@base[name] + filter_specs(@all_specs[name], package)).uniq {|spec| [spec.version.hash, spec.platform] }
 
       if name == "bundler" && !bundler_pinned_to_current_version?
         bundler_spec = Gem.loaded_specs["bundler"]
@@ -368,12 +377,22 @@ module Bundler
       end
     end
 
+    def filter_specs(specs, package)
+      filter_remote_specs(filter_prereleases(specs, package), package)
+    end
+
     def filter_prereleases(specs, package)
       return specs unless package.ignores_prereleases? && specs.size > 1
 
       specs.reject {|s| s.version.prerelease? }
     end
 
+    def filter_remote_specs(specs, package)
+      return specs unless package.prefer_local?
+
+      specs.select {|s| s.is_a?(StubSpecification) }
+    end
+
     # Ignore versions that depend on themselves incorrectly
     def filter_invalid_self_dependencies(specs, name)
       specs.reject do |s|
@@ -405,10 +424,13 @@ module Bundler
 
         dep_range = dep_constraint.range
         versions = select_sorted_versions(dep_package, dep_range)
-        if versions.empty? && dep_package.ignores_prereleases?
-          @all_versions.delete(dep_package)
-          @sorted_versions.delete(dep_package)
-          dep_package.consider_prereleases!
+        if versions.empty?
+          if dep_package.ignores_prereleases? || dep_package.prefer_local?
+            @all_versions.delete(dep_package)
+            @sorted_versions.delete(dep_package)
+          end
+          dep_package.consider_prereleases! if dep_package.ignores_prereleases?
+          dep_package.consider_remote_versions! if dep_package.prefer_local?
           versions = select_sorted_versions(dep_package, dep_range)
         end
 
diff --git a/lib/bundler/resolver/base.rb b/lib/bundler/resolver/base.rb
index b0c5c58047..3f2436672a 100644
--- a/lib/bundler/resolver/base.rb
+++ b/lib/bundler/resolver/base.rb
@@ -72,6 +72,12 @@ module Bundler
         end
       end
 
+      def include_remote_specs(names)
+        names.each do |name|
+          get_package(name).consider_remote_versions!
+        end
+      end
+
       private
 
       def indirect_pins(names)
diff --git a/lib/bundler/resolver/package.rb b/lib/bundler/resolver/package.rb
index 16c43d05af..5aecc12d05 100644
--- a/lib/bundler/resolver/package.rb
+++ b/lib/bundler/resolver/package.rb
@@ -15,7 +15,7 @@ module Bundler
     class Package
       attr_reader :name, :platforms, :dependency, :locked_version
 
-      def initialize(name, platforms, locked_specs:, unlock:, prerelease: false, dependency: nil)
+      def initialize(name, platforms, locked_specs:, unlock:, prerelease: false, prefer_local: false, dependency: nil)
         @name = name
         @platforms = platforms
         @locked_version = locked_specs[name].first&.version
@@ -23,6 +23,7 @@ module Bundler
         @dependency = dependency || Dependency.new(name, @locked_version)
         @top_level = !dependency.nil?
         @prerelease = @dependency.prerelease? || @locked_version&.prerelease? || prerelease ? :consider_first : :ignore
+        @prefer_local = prefer_local
       end
 
       def platform_specs(specs)
@@ -69,6 +70,14 @@ module Bundler
         @prerelease = :consider_last
       end
 
+      def prefer_local?
+        @prefer_local
+      end
+
+      def consider_remote_versions!
+        @prefer_local = false
+      end
+
       def force_ruby_platform?
         @dependency.force_ruby_platform
       end