fetch/build formula from source when modified

closes Homebrew/homebrew#36068

Closes Homebrew/homebrew#41397.

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

Library/Homebrew/cmd/fetch.rb

@@ -32,6 +32,13 @@ module Homebrew
   def fetch_bottle? f
     return true if ARGV.force_bottle? && f.bottle
     return false unless f.bottle && f.pour_bottle?
+    if f.file_modified?
+      filename = f.path.to_s.gsub("#{HOMEBREW_PREFIX}/", "")
+      opoo "Formula file is modified!"
+      puts "Fetching source because #{filename} has local changes"
+      puts "To fetch the bottle instead, run with --force-bottle"
+      return false
+    end
     return false if ARGV.build_from_source? || ARGV.build_bottle?
     return false unless f.bottle.compatible_cellar?
     return true

Library/Homebrew/formula.rb

@@ -601,6 +601,14 @@ class Formula
     s << ") #{path}>"
   end
 
+  def file_modified?
+    return false unless which("git")
+    path.parent.cd do
+      diff = Utils.popen_read("git", "diff", "origin/master", "--", "#{path}")
+      !diff.empty? && $?.exitstatus == 0
+    end
+  end
+
   # Standard parameters for CMake builds.
   # Setting CMAKE_FIND_FRAMEWORK to "LAST" tells CMake to search for our
   # libraries before trying to utilize Frameworks, many of which will be from
@@ -1187,4 +1195,3 @@ class Formula
     end
   end
 end
-

Library/Homebrew/formula_installer.rb

@@ -62,7 +62,7 @@ class FormulaInstaller
 
     bottle = formula.bottle
     return true  if force_bottle? && bottle
-    return false if build_from_source? || build_bottle? || interactive?
+    return false if build_from_source? || build_bottle? || interactive? || formula.file_modified?
     return false unless options.empty?
 
     return true if formula.local_bottle_path
@@ -180,6 +180,12 @@ class FormulaInstaller
     build_bottle_preinstall if build_bottle?
 
     unless @poured_bottle
+      if formula.file_modified?
+        filename = formula.path.to_s.gsub("#{HOMEBREW_PREFIX}/", "")
+        opoo "Formula file is modified!"
+        puts "Building from source because #{filename} has local changes"
+        puts "To install from a bottle instead, run with --force-bottle"
+      end
       compute_and_install_dependencies if @pour_failed and not ignore_deps?
       build
       clean

Library/Homebrew/test/test_bottle_hooks.rb

@@ -7,6 +7,7 @@ class BottleHookTests < Homebrew::TestCase
     def bottle; end
     def local_bottle_path; end
     def some_random_method; true; end
+    def file_modified?; end
   end
 
   def setup