Only brew desc --search needs --eval-all

- It was suggested in https://github.com/Homebrew/brew/issues/ 16733 that
  `brew desc <formula_or_cask>` should work like `brew info <formula_or_cask>`
  and print the description of the package without needing `--eval-all`.
- Looking at the code, it seems like it's only searching that needs
  `--eval-all`, so limit the check to that.

Before:

```shell
$ brew desc hello
Error: `brew desc` needs `--eval-all` passed or `HOMEBREW_EVAL_ALL` set!
```

After:

```shell
$ brew desc hello
hello: Program providing model for GNU coding standards and practices

$ brew desc --search hello
Error: Invalid usage: `brew desc --search` needs `--eval-all` passed or `HOMEBREW_EVAL_ALL` set!

$ brew desc --search --eval-all hello
==> Formulae
dsh: Dancer's shell, or distributed shell
hello: Program providing model for GNU coding standards and practices
```

Library/Homebrew/cmd/desc.rb

@@ -38,10 +38,6 @@ module Homebrew
 
       sig { override.void }
       def run
-        if !args.eval_all? && !Homebrew::EnvConfig.eval_all?
-          raise UsageError, "`brew desc` needs `--eval-all` passed or `HOMEBREW_EVAL_ALL` set!"
-        end
-
         search_type = if args.search?
           :either
         elsif args.name?
@@ -50,7 +46,16 @@ module Homebrew
           :desc
         end
 
-        if search_type.blank?
+        if search_type.present?
+          if !args.eval_all? && !Homebrew::EnvConfig.eval_all?
+            raise UsageError, "`brew desc --search` needs `--eval-all` passed or `HOMEBREW_EVAL_ALL` set!"
+          end
+
+          query = args.named.join(" ")
+          string_or_regex = Search.query_regexp(query)
+          return Search.search_descriptions(string_or_regex, args, search_type:)
+        end
+
         desc = {}
         args.named.to_formulae_and_casks.each do |formula_or_cask|
           case formula_or_cask
@@ -64,11 +69,6 @@ module Homebrew
           end
         end
         Descriptions.new(desc).print
-        else
-          query = args.named.join(" ")
-          string_or_regex = Search.query_regexp(query)
-          Search.search_descriptions(string_or_regex, args, search_type:)
-        end
       end
     end
   end

Library/Homebrew/test/cmd/desc_spec.rb

@@ -9,9 +9,25 @@ RSpec.describe Homebrew::Cmd::Desc do
   it "shows a given Formula's description", :integration_test do
     setup_test_formula "testball"
 
-    expect { brew "desc", "--eval-all", "testball" }
+    expect { brew "desc", "testball" }
       .to output("testball: Some test\n").to_stdout
       .and not_to_output.to_stderr
       .and be_a_success
   end
+
+  it "errors when searching without --eval-all", :integration_test do
+    setup_test_formula "testball"
+
+    expect { brew "desc", "--search", "testball" }
+      .to output(/`brew desc --search` needs `--eval-all` passed or `HOMEBREW_EVAL_ALL` set!/).to_stderr
+      .and be_a_failure
+  end
+
+  it "successfully searches with --search --eval-all", :integration_test do
+    setup_test_formula "testball"
+
+    expect { brew "desc", "--search", "--eval-all", "ball" }
+      .to output(/testball: Some test/).to_stdout
+      .and not_to_output.to_stderr
+  end
 end