Auto-heal on corrupted lockfile with missing deps

Following up on rubygems#6355, which
turned a crash into a nicer error message, this commit auto-heals the
corrupt lockfile instead.

Since in this particular case (a corrupt Gemfile.lock with missing
dependencies) the LazySpecification will not have accurate dependency
information, we have to materialize the SpecSet to determine there are
missing dependencies. Since we've already got some
incomplete-spec-auto-healing here, I've treated this as another brand of
incomplete spec.

bundler/lib/bundler/spec_set.rb

@@ -78,7 +78,7 @@ def to_hash
     def materialize(deps)
       materialized = self.for(deps, true)
 
-      SpecSet.new(materialized, incomplete_specs)
+      SpecSet.new(materialized, incomplete_specs + specs_with_missing_dependencies(materialized))
     end
 
     # Materialize for all the specs in the spec set, regardless of what platform they're for
@@ -202,5 +202,15 @@ def tsort_each_child(s)
         lookup[d.name].each {|s2| yield s2 }
       end
     end
+
+    def specs_with_missing_dependencies(materialized)
+      materialized.
+        select {|spec| missing_dependencies?(spec) }.
+        flat_map {|spec| lookup[spec.name] }
+    end
+
+    def missing_dependencies?(spec)
+      spec.dependencies.any? {|dep| lookup[dep.name].empty? }
+    end
   end
 end

bundler/spec/lock/lockfile_spec.rb

@@ -1221,7 +1221,7 @@
       and include("Either installing with `--full-index` or running `bundle update rack_middleware` should fix the problem.")
   end
 
-  it "errors gracefully on a corrupt lockfile" do
+  it "auto-heals when the lockfile is missing dependent specs" do
     build_repo4 do
       build_gem "minitest-bisect", "1.6.0" do |s|
         s.add_dependency "path_expander", "~> 1.1"
@@ -1253,10 +1253,25 @@
     L
 
     cache_gems "minitest-bisect-1.6.0", "path_expander-1.1.1", :gem_repo => gem_repo4
-    bundle :install, :raise_on_error => false
+    bundle :install
 
-    expect(err).not_to include("ERROR REPORT TEMPLATE")
-    expect(err).to include("path_expander (~> 1.1), dependency of minitest-bisect-1.6.0 but missing from lockfile")
+    expect(lockfile).to eq <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}/
+        specs:
+          minitest-bisect (1.6.0)
+            path_expander (~> 1.1)
+          path_expander (1.1.1)
+
+      PLATFORMS
+        #{lockfile_platforms}
+
+      DEPENDENCIES
+        minitest-bisect
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
   end
 
   it "auto-heals when the lockfile is missing specs" do