cmd/log: improve output messaging.

This wasn’t adapted to the new, multiple repository world.

Library/Homebrew/cmd/log.rb

@@ -9,20 +9,32 @@ module Homebrew
 
   def log
     if ARGV.named.empty?
-      cd HOMEBREW_REPOSITORY
-      git_log
+      git_log HOMEBREW_REPOSITORY
     else
       path = Formulary.path(ARGV.named.first)
-      cd path.dirname # supports taps
-      git_log path
+      tap = Tap.from_path(path)
+      git_log path.dirname, path, tap
     end
   end
 
-  def git_log(path = nil)
-    if File.exist? "#{`git rev-parse --show-toplevel`.chomp}/.git/shallow"
+  def git_log(cd_dir, path = nil, tap = nil)
+    cd cd_dir
+    repo = Utils.popen_read("git rev-parse --show-toplevel").chomp
+    if tap
+      name = tap.to_s
+      git_cd = "$(brew --repo #{tap})"
+    elsif cd_dir == HOMEBREW_REPOSITORY
+      name = "Homebrew/brew"
+      git_cd = "$(brew --repo)"
+    else
+      name, git_cd = cd_dir
+    end
+
+    if File.exist? "#{repo}/.git/shallow"
       opoo <<-EOS.undent
-        The git repository is a shallow clone therefore the filtering may be incorrect.
-        Use `git fetch --unshallow` to get the full repository.
+        #{name} is a shallow clone so only partial output will be shown.
+        To get a full clone run:
+          git -C "#{git_cd}" fetch --unshallow
       EOS
     end
     args = ARGV.options_only

Library/Homebrew/test/cmd/log_spec.rb

@@ -33,7 +33,7 @@ describe "brew log", :integration_test do
 
     expect { brew "log", "#{shallow_tap}/testball" }
       .to output(/This is a test commit for Testball/).to_stdout
-      .and output(/Warning: The git repository is a shallow clone/).to_stderr
+      .and output(%r{Warning: homebrew/shallow is a shallow clone}).to_stderr
       .and be_a_success
 
     expect(shallow_tap.path/".git/shallow").to exist, "A shallow clone should have been created."