tab: use cache to avoid rereading the same files.

Closes Homebrew/homebrew#46400.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/tab.rb

@@ -9,6 +9,11 @@ require "utils/json"
 # `Tab.create`.
 class Tab < OpenStruct
   FILENAME = "INSTALL_RECEIPT.json"
+  CACHE = {}
+
+  def self.clear_cache
+    CACHE.clear
+  end
 
   def self.create(formula, compiler, stdlib, build)
     attributes = {
@@ -32,7 +37,7 @@ class Tab < OpenStruct
   end
 
   def self.from_file(path)
-    from_file_content(File.read(path), path)
+    CACHE.fetch(path) { |p| CACHE[p] = from_file_content(File.read(p), p) }
   end
 
   def self.from_file_content(content, path)
@@ -217,6 +222,7 @@ class Tab < OpenStruct
   end
 
   def write
+    CACHE[tabfile] = self
     tabfile.atomic_write(to_json)
   end
 

Library/Homebrew/test/test_formula_installer.rb

@@ -20,10 +20,12 @@ class InstallTests < Homebrew::TestCase
     assert_predicate formula, :installed?
 
     begin
+      Tab.clear_cache
       refute_predicate Tab.for_keg(keg), :poured_from_bottle
 
       yield formula
     ensure
+      Tab.clear_cache
       keg.unlink
       keg.uninstall
       formula.clear_cache