Don't filter the environment for brew bundle (exec|env|sh)

It's both unexpected and undesirable for `brew bundle (exec|env|sh)` to
filter the environment and makes these tools less useful.

Not filtering the environment, though, causes issues with the
`brew bundle sh` shell. Fix this up and, while we're here, also improve
the formatting for both `zsh` and `bash` (the default) to use nicer and
more consistent prompts and colours.

To simplify this, consolidate some logic in a new
`Utils::Shell.shell_with_prompt` method and add tests for it and a
similar notice for `brew bundle sh`.

Finally, avoid printing out the notice when `HOMEBREW_NO_ENV_HINTS` is
set.

Library/Homebrew/cmd/bundle.rb

@@ -210,18 +210,17 @@ module Homebrew
             _subcommand, *named_args = args.named
             named_args
           when "sh"
-            preferred_shell = Utils::Shell.preferred_path(default: "/bin/bash")
-            subshell = case Utils::Shell.preferred
-            when :zsh
-              "PS1='brew bundle %B%F{green}%~%f%b$ ' #{preferred_shell} -d -f"
-            when :bash
-              "PS1=\"brew bundle \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell} --noprofile --norc"
-            else
-              "PS1=\"brew bundle \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell}"
+            preferred_path = Utils::Shell.preferred_path(default: "/bin/bash")
+            notice = unless Homebrew::EnvConfig.no_env_hints?
+              <<~EOS
+                Your shell has been configured to use a build environment from your `Brewfile`.
+                This should help you build stuff.
+                Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
+                When done, type `exit`.
+              EOS
             end
-            $stdout.flush
             ENV["HOMEBREW_FORCE_API_AUTO_UPDATE"] = nil
-            [subshell]
+            [Utils::Shell.shell_with_prompt("brew bundle", preferred_path:, notice:)]
           when "env"
             ["env"]
           end

Library/Homebrew/dev-cmd/sh.rb

@@ -39,32 +39,25 @@ module Homebrew
 
         ENV["VERBOSE"] = "1" if args.verbose?
 
-        preferred_shell = Utils::Shell.preferred_path(default: "/bin/bash")
+        preferred_path = Utils::Shell.preferred_path(default: "/bin/bash")
 
         if args.cmd.present?
-          safe_system(preferred_shell, "-c", args.cmd)
+          safe_system(preferred_path, "-c", args.cmd)
         elsif args.named.present?
-          safe_system(preferred_shell, args.named.first)
+          safe_system(preferred_path, args.named.first)
         else
-          shell_type = Utils::Shell.preferred
-          subshell = case shell_type
-          when :zsh
-            "PS1='brew %B%F{green}%~%f%b$ ' #{preferred_shell} -d -f"
-          when :bash
-            "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell} --noprofile --norc"
-          else
-            "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell}"
-          end
-          puts <<~EOS
+          notice = unless Homebrew::EnvConfig.no_env_hints?
+            <<~EOS
               Your shell has been configured to use Homebrew's build environment;
               this should help you build stuff. Notably though, the system versions of
               gem and pip will ignore our configuration and insist on using the
               environment they were built under (mostly). Sadly, scons will also
               ignore our configuration.
+              Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
               When done, type `exit`.
             EOS
-          $stdout.flush
-          safe_system subshell
+          end
+          system Utils::Shell.shell_with_prompt("brew", preferred_path:, notice:)
         end
       end
     end

Library/Homebrew/test/utils/shell_spec.rb

@@ -105,4 +105,26 @@ RSpec.describe Utils::Shell do
         .to eq("fish_add_path #{path}")
     end
   end
+
+  describe "::shell_with_prompt" do
+    it "returns zsh-specific prompt configuration" do
+      ENV["SHELL"] = "/bin/zsh"
+      expect(described_class.shell_with_prompt("test", preferred_path: "/bin/zsh", notice: "")).to eq(
+        "PROMPT='%B%F{green}test%f %F{blue}$%f%b ' RPROMPT='[%B%F{red}%~%f%b]' /bin/zsh -f",
+      )
+    end
+
+    it "returns generic shell prompt configuration" do
+      ENV["SHELL"] = "/bin/bash"
+      expect(described_class.shell_with_prompt("test", preferred_path: "/bin/bash", notice: "")).to eq(
+        "PS1=\"\\[\\033[1;32m\\]brew \\[\\033[1;31m\\]\\w \\[\\033[1;34m\\]$\\[\\033[0m\\] \" /bin/bash",
+      )
+    end
+
+    it "outputs notice when provided" do
+      notice = "Test Notice"
+      expect { described_class.shell_with_prompt("test", preferred_path: "/bin/bash", notice: notice) }
+        .to output("#{notice}\n").to_stdout
+    end
+  end
 end

Library/Homebrew/utils/shell.rb

@@ -152,5 +152,21 @@ module Utils
       str.gsub!("\n", "'\n'")
       str
     end
+
+    sig { params(type: String, preferred_path: String, notice: T.nilable(String)).returns(String) }
+    def shell_with_prompt(type, preferred_path:, notice:)
+      preferred = from_path(preferred_path)
+      subshell = case preferred
+      when :zsh
+        "PROMPT='%B%F{green}#{type}%f %F{blue}$%f%b ' RPROMPT='[%B%F{red}%~%f%b]' #{preferred_path} -f"
+      else
+        "PS1=\"\\[\\033[1;32m\\]brew \\[\\033[1;31m\\]\\w \\[\\033[1;34m\\]$\\[\\033[0m\\] \" #{preferred_path}"
+      end
+
+      puts notice if notice.present?
+      $stdout.flush
+
+      subshell
+    end
   end
 end

bin/brew

@@ -265,6 +265,16 @@ then
   export HOMEBREW_GITHUB_HOSTED_RUNNER=1
 fi
 
+# don't filter the environment for `brew bundle (exec|env|sh)`
+if [[ "${1:-}" == "bundle" ]]
+then
+  if [[ "${2:-}" == "exec" || "${2:-}" == "env" || "${2:-}" == "sh" ]]
+  then
+    exec /bin/bash -p "${HOMEBREW_LIBRARY}/Homebrew/brew.sh" "$@"
+    exit $?
+  fi
+fi
+
 # filter the user environment
 PATH="/usr/bin:/bin:/usr/sbin:/sbin"