From 7df90eb7e1d3c1d32b99daf9206d57591d2a5a93 Mon Sep 17 00:00:00 2001
From: Harry Marr <harry.marr@gmail.com>
Date: Mon, 2 May 2022 19:53:44 -0400
Subject: [PATCH] Support git partial clones with sparse checkouts

---
 Library/Homebrew/cask/url.rb          | 10 +++++++--
 Library/Homebrew/download_strategy.rb | 30 +++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/Library/Homebrew/cask/url.rb b/Library/Homebrew/cask/url.rb
index 6221f0414e..f692b0f0e5 100644
--- a/Library/Homebrew/cask/url.rb
+++ b/Library/Homebrew/cask/url.rb
@@ -15,7 +15,7 @@ class URL < Delegator
                 :verified, :using,
                 :tag, :branch, :revisions, :revision,
                 :trust_cert, :cookies, :referer, :header, :user_agent,
-                :data
+                :data, :only_paths
 
     extend Forwardable
     def_delegators :uri, :path, :scheme, :to_s
@@ -36,6 +36,7 @@ class URL < Delegator
         header:     T.nilable(String),
         user_agent: T.nilable(T.any(Symbol, String)),
         data:       T.nilable(T::Hash[String, String]),
+        only_paths: T.nilable(T::Array[String]),
       ).void
     }
     def initialize(
@@ -51,7 +52,8 @@ class URL < Delegator
       referer: nil,
       header: nil,
       user_agent: nil,
-      data: nil
+      data: nil,
+      only_paths: nil
     )
 
       @uri = URI(uri)
@@ -69,6 +71,7 @@ class URL < Delegator
       specs[:header]     = @header     = header
       specs[:user_agent] = @user_agent = user_agent || :default
       specs[:data]       = @data       = data
+      specs[:only_paths] = @only_paths = only_paths
 
       @specs = specs.compact
     end
@@ -156,6 +159,7 @@ class URL < Delegator
       header:          T.nilable(String),
       user_agent:      T.nilable(T.any(Symbol, String)),
       data:            T.nilable(T::Hash[String, String]),
+      only_paths:      T.nilable(T::Array[String]),
       caller_location: Thread::Backtrace::Location,
       dsl:             T.nilable(Cask::DSL),
       block:           T.nilable(T.proc.params(arg0: T.all(String, BlockDSL::PageWithURL)).returns(T.untyped)),
@@ -175,6 +179,7 @@ class URL < Delegator
     header: nil,
     user_agent: nil,
     data: nil,
+    only_paths: nil,
     caller_location: T.must(caller_locations).fetch(0),
     dsl: nil,
     &block
@@ -202,6 +207,7 @@ class URL < Delegator
         header:     header,
         user_agent: user_agent,
         data:       data,
+        only_paths: only_paths,
       )
     end
     )
diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index c53e62d99b..d3aead0c4c 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -814,6 +814,7 @@ class GitDownloadStrategy < VCSDownloadStrategy
     super
     @ref_type ||= :branch
     @ref ||= "master"
+    @only_paths = meta[:only_paths]
   end
 
   # @see AbstractDownloadStrategy#source_modified_time
@@ -880,6 +881,14 @@ class GitDownloadStrategy < VCSDownloadStrategy
     (cached_location/".gitmodules").exist?
   end
 
+  def partial_clone_sparse_checkout?
+    return false if @only_paths.nil?
+
+    # There is some support for partial clones prior to 2.20, but we avoid using it
+    # due to performance issues
+    Version.create(Utils::Git.version) >= Version.create("2.20.0")
+  end
+
   sig { returns(T::Array[String]) }
   def clone_args
     args = %w[clone]
@@ -889,6 +898,8 @@ class GitDownloadStrategy < VCSDownloadStrategy
       args << "--branch" << @ref
     end
 
+    args << "--no-checkout" << "--filter=blob:none" if partial_clone_sparse_checkout?
+
     args << "-c" << "advice.detachedHead=false" # silences detached head warning
     args << @url << cached_location
   end
@@ -922,6 +933,13 @@ class GitDownloadStrategy < VCSDownloadStrategy
     command! "git",
              args:  ["config", "advice.detachedHead", "false"],
              chdir: cached_location
+
+    if partial_clone_sparse_checkout?
+      command! "git",
+               args:  ["config", "origin.partialclonefilter", "blob:none"],
+               chdir: cached_location
+      configure_sparse_checkout
+    end
   end
 
   sig { params(timeout: T.nilable(Time)).void }
@@ -950,6 +968,9 @@ class GitDownloadStrategy < VCSDownloadStrategy
              args:    ["config", "homebrew.cacheversion", cache_version],
              chdir:   cached_location,
              timeout: timeout&.remaining
+
+    configure_sparse_checkout if partial_clone_sparse_checkout?
+
     checkout(timeout: timeout)
     update_submodules(timeout: timeout) if submodules?
   end
@@ -1020,6 +1041,15 @@ class GitDownloadStrategy < VCSDownloadStrategy
       dot_git.atomic_write("gitdir: #{relative_git_dir}\n")
     end
   end
+
+  def configure_sparse_checkout
+    command! "git",
+             args:  ["config", "core.sparseCheckout", "true"],
+             chdir: cached_location
+
+    sparse_checkout_paths = @only_paths.join("\n") + "\n"
+    (git_dir/"info"/"sparse-checkout").atomic_write(sparse_checkout_paths)
+  end
 end
 
 # Strategy for downloading a Git repository from GitHub.