Improve error message when strict resolution filters out everything

bundler/lib/bundler/resolver.rb

@@ -342,6 +342,17 @@ def filtered_versions_for(package)
       @gem_version_promoter.filter_versions(package, @all_versions[package])
     end
 
+    def raise_all_versions_filtered_out!(package)
+      level = @gem_version_promoter.level
+      name = package.name
+      locked_version = package.locked_version
+      requirement = package.dependency
+
+      raise GemNotFound,
+        "#{name} is locked to #{locked_version}, while Gemfile is requesting #{requirement}. " \
+        "--strict --#{level} was specified, but there are no #{level} level upgrades from #{locked_version} satisfying #{requirement}, so version solving has failed"
+    end
+
     def filter_matching_specs(specs, requirements)
       Array(requirements).flat_map do |requirement|
         specs.select {| spec| requirement_satisfied_by?(requirement, spec) }
@@ -391,6 +402,11 @@ def prepare_dependencies(requirements, packages)
           dep_package.consider_prereleases!
           versions = select_sorted_versions(dep_package, dep_range)
         end
+
+        if versions.empty? && select_all_versions(dep_package, dep_range).any?
+          raise_all_versions_filtered_out!(dep_package)
+        end
+
         next [dep_package, dep_constraint] unless versions.empty?
 
         next unless dep_package.current_platform?
@@ -403,6 +419,10 @@ def select_sorted_versions(package, range)
       range.select_versions(@sorted_versions[package])
     end
 
+    def select_all_versions(package, range)
+      range.select_versions(@all_versions[package])
+    end
+
     def other_specs_matching_message(specs, requirement)
       message = String.new("The source contains the following gems matching '#{requirement}':\n")
       message << specs.map {|s| "  * #{s.full_name}" }.join("\n")

bundler/spec/commands/lock_spec.rb

@@ -392,6 +392,22 @@
       expect(the_bundle.locked_gems.specs.map(&:full_name)).to eq(%w[foo-1.5.0 bar-2.1.1 qux-1.1.0].sort)
     end
 
+    it "shows proper error when Gemfile changes forbid patch upgrades, and --patch --strict is given" do
+      # force next minor via Gemfile
+      gemfile <<-G
+        source "#{file_uri_for(gem_repo4)}"
+        gem 'foo', '1.5.0'
+        gem 'qux'
+      G
+
+      bundle "lock --update foo --patch --strict", raise_on_error: false
+
+      expect(err).to include(
+        "foo is locked to 1.4.3, while Gemfile is requesting foo (= 1.5.0). " \
+        "--strict --patch was specified, but there are no patch level upgrades from 1.4.3 satisfying foo (= 1.5.0), so version solving has failed"
+      )
+    end
+
     context "pre" do
       it "defaults to major" do
         bundle "lock --update --pre"