Display collected caveats at end of install or upgrade

Library/Homebrew/cmd/install.rb

@@ -249,6 +249,7 @@ def install
         Migrator.migrate_if_needed(f)
         install_formula(f)
       end
+      Homebrew.messages.display_messages
     rescue FormulaUnreadableError, FormulaClassUnavailableError,
            TapFormulaUnreadableError, TapFormulaClassUnavailableError => e
       # Need to rescue before `FormulaUnavailableError` (superclass of this)

Library/Homebrew/cmd/reinstall.rb

@@ -3,6 +3,7 @@
 
 require "formula_installer"
 require "development_tools"
+require "messages"
 
 module Homebrew
   module_function
@@ -18,6 +19,7 @@ def reinstall
       Migrator.migrate_if_needed(f)
       reinstall_formula(f)
     end
+    Homebrew.messages.display_messages
   end
 
   def reinstall_formula(f)

Library/Homebrew/cmd/upgrade.rb

@@ -21,6 +21,7 @@
 require "formula_installer"
 require "cleanup"
 require "development_tools"
+require "messages"
 
 module Homebrew
   module_function
@@ -102,6 +103,7 @@ def upgrade
         onoe "#{f}: #{e}"
       end
     end
+    Homebrew.messages.display_messages
   end
 
   def upgrade_formula(f)

Library/Homebrew/formula_installer.rb

@@ -14,6 +14,7 @@
 require "cache_store"
 require "linkage_checker"
 require "install"
+require "messages"
 
 class FormulaInstaller
   include FormulaCellarChecks
@@ -348,6 +349,7 @@ def install
     build_bottle_postinstall if build_bottle?
 
     opoo "Nothing was installed to #{formula.prefix}" unless formula.installed?
+    Homebrew.messages.formula_installed(formula)
   end
 
   def check_conflicts
@@ -604,6 +606,7 @@ def caveats
     return if caveats.empty?
     @show_summary_heading = true
     ohai "Caveats", caveats.to_s
+    Homebrew.messages.record_caveats(formula, caveats)
   end
 
   def finish

Library/Homebrew/global.rb

@@ -1,6 +1,7 @@
 require "pathname"
 require "English"
 require "ostruct"
+require "messages"
 
 require "pp"
 require "extend/ARGV"
@@ -49,6 +50,10 @@ def args
       @args ||= OpenStruct.new
     end
 
+    def messages
+      @messages ||= Messages.new
+    end
+
     def raise_deprecation_exceptions?
       @raise_deprecation_exceptions == true
     end

Library/Homebrew/messages.rb

@@ -0,0 +1,31 @@
+# A Messages object collects messages that may need to be displayed together
+# at the end of a multi-step `brew` command run
+class Messages
+  attr_reader :caveats, :formula_count
+
+  def initialize
+    @caveats = []
+    @formula_count = 0
+  end
+
+  def record_caveats(f, caveats)
+    @caveats.push(formula: f.name, caveats: caveats)
+  end
+
+  def formula_installed(_f)
+    @formula_count += 1
+  end
+
+  def display_messages
+    display_caveats
+  end
+
+  def display_caveats
+    return if @formula_count <= 1
+    return if @caveats.empty?
+    oh1 "Caveats"
+    @caveats.each do |c|
+      ohai c[:formula], c[:caveats]
+    end
+  end
+end

Library/Homebrew/test/messages_spec.rb

@@ -0,0 +1,36 @@
+require "messages"
+require "spec_helper"
+
+describe Messages do
+  before do
+    @m = Messages.new
+    f_foo = formula("foo") do
+      url "http://example.com/foo-0.1.tgz"
+    end
+    f_bar = formula("bar") do
+      url "http://example.com/bar-0.1.tgz"
+    end
+    f_baz = formula("baz") do
+      url "http://example.com/baz-0.1.tgz"
+    end
+    @m.formula_installed(f_foo)
+    @m.record_caveats(f_foo, "Zsh completions were installed")
+    @m.formula_installed(f_bar)
+    @m.record_caveats(f_bar, "Keg-only formula")
+    @m.formula_installed(f_baz)
+    @m.record_caveats(f_baz, "A valid GOPATH is required to use the go command")
+  end
+
+  it "has the right installed-formula count" do
+    expect(@m.formula_count).to equal(3)
+  end
+
+  it "has recorded caveats" do
+    expect(@m.caveats).to_not be_empty
+  end
+
+  it "maintained the order of recorded caveats" do
+    caveats_formula_order = @m.caveats.map { |x| x[:formula] }
+    expect(caveats_formula_order).to eq(["foo", "bar", "baz"])
+  end
+end