Stop resolving locally for empty CHECKSUMS entries

lib/bundler/definition.rb

@@ -198,7 +198,7 @@ def setup_domain!(options = {})
 
       sources.cached!
 
-      if options[:add_checksums] || (!options[:local] && (install_needed? || refetch_needed?(options)))
+      if options[:add_checksums] || (!options[:local] && (install_needed? || refetch_needed?(options) || @locked_spec_with_empty_checksums))
         sources.remote!
         true
       else
@@ -650,7 +650,7 @@ def something_changed?
         @missing_lockfile_dep ||
         @unlocking_bundler ||
         @locked_spec_with_missing_checksums ||
-        @locked_spec_with_empty_checksums ||
+        empty_checksums_actionable? ||
         @locked_spec_with_missing_deps ||
         @locked_spec_with_invalid_deps
     end
@@ -659,6 +659,16 @@ def resolve_needed?
       unlocking? || something_changed?
     end
 
+    # Only a remote fetch can fill an empty CHECKSUMS entry, so it justifies a
+    # resolution only when one is coming. Resolving locally for it would repeat
+    # on every `Bundler.setup` without changing the lockfile. Frozen mode still
+    # has to refuse the entry.
+    def empty_checksums_actionable?
+      return false unless @locked_spec_with_empty_checksums
+
+      Bundler.frozen_bundle? || !sources.local_mode?
+    end
+
     def should_add_extra_platforms?
       !lockfile_exists? && Bundler::MatchPlatform.generic_local_platform_is_ruby? && !Bundler.settings[:force_ruby_platform]
     end

spec/lock/lockfile_spec.rb

@@ -1682,6 +1682,36 @@
     expect(the_bundle).not_to include_gems "myrack 0.9.1"
   end
 
+  it "fills empty CHECKSUMS entries when not frozen, even if every gem is already installed" do
+    system_gems "myrack-0.9.1", gem_repo: gem_repo2
+
+    lockfile <<-L
+      GEM
+        remote: https://gem.repo2/
+        specs:
+          myrack (0.9.1)
+
+      PLATFORMS
+        #{lockfile_platforms}
+
+      DEPENDENCIES
+        myrack
+
+      CHECKSUMS
+        myrack (0.9.1)
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    install_gemfile <<-G
+      source "https://gem.repo2"
+      gem "myrack"
+    G
+
+    expect(lockfile).to include("  #{checksum_to_lock(gem_repo2, "myrack", "0.9.1")}\n")
+  end
+
   it "automatically fixes the lockfile when it's missing deps, they conflict with other locked deps, but conflicts are fixable" do
     build_repo4 do
       build_gem "other_dep", "0.9"

spec/runtime/setup_spec.rb

@@ -259,6 +259,24 @@ def clean_load_path(lp)
     expect(bundled_app_lock).to exist
   end
 
+  it "does not resolve again for the empty CHECKSUMS entries it locked itself" do
+    system_gems "myrack-1.0.0"
+
+    gemfile <<-G
+      source "https://gem.repo1"
+      gem "myrack"
+    G
+
+    ruby "require 'bundler'; Bundler.setup"
+    expect(out).to include("Resolving dependencies...")
+    lockfile = File.read(bundled_app_lock)
+    expect(lockfile).to include("CHECKSUMS\n  myrack (1.0.0)\n")
+
+    ruby "require 'bundler'; Bundler.setup"
+    expect(out).not_to include("Resolving dependencies...")
+    expect(File.read(bundled_app_lock)).to eq(lockfile)
+  end
+
   describe "$BUNDLE_GEMFILE" do
     context "user provides an absolute path" do
       it "uses BUNDLE_GEMFILE to locate the gemfile if present" do