cmd/switch: improve usability.

- Ensure that we output the available versions where relevant
- Use `<formula>` to be consistent with other commands’ help
- General code cleanup

Library/Homebrew/cmd/switch.rb

@@ -1,5 +1,5 @@
-#:  * `switch` <name> <version>:
-#:    Symlink all of the specific <version> of <name>'s install to Homebrew prefix.
+#:  * `switch` <formula> <version>:
+#:    Symlink all of the specific <version> of <formula>'s install to Homebrew prefix.
 
 require "formula"
 require "keg"
@@ -9,14 +9,15 @@ module Homebrew
   module_function
 
   def switch
-    if ARGV.named.length != 2
-      onoe "Usage: brew switch <name> <version>"
+    name = ARGV.first
+
+    usage = "Usage: brew switch <formula> <version>"
+
+    unless name
+      onoe usage
       exit 1
     end
 
-    name = ARGV.shift
-    version = ARGV.shift
-
     rack = Formulary.to_rack(name)
 
     unless rack.directory?
@@ -24,13 +25,21 @@ module Homebrew
       exit 2
     end
 
-    # Does the target version exist?
+    versions = rack.subdirs
+                   .map { |d| Keg.new(d).version }
+                   .sort
+                   .join(", ")
+    version = ARGV[1]
+
+    if !version || ARGV.named.length > 2
+      onoe usage
+      puts "#{name} installed versions: #{versions}"
+      exit 1
+    end
+
     unless (rack/version).directory?
       onoe "#{name} does not have a version \"#{version}\" in the Cellar."
-
-      versions = rack.subdirs.map { |d| Keg.new(d).version }.sort
-      puts "Versions available: #{versions.join(", ")}"
-
+      puts "#{name} installed versions: #{versions}"
       exit 3
     end
 

Library/Homebrew/test/cmd/switch_spec.rb

@@ -1,7 +1,7 @@
 describe "brew switch", :integration_test do
   it "allows switching between Formula versions" do
     expect { brew "switch" }
-      .to output(/Usage: brew switch <name> <version>/).to_stderr
+      .to output(/Usage: brew switch <formula> <version>/).to_stderr
       .and not_to_output.to_stdout
       .and be_a_failure
 
@@ -25,7 +25,7 @@ describe "brew switch", :integration_test do
       .and be_a_success
 
     expect { brew "switch", "testball", "0.3" }
-      .to output("Versions available: 0.1, 0.2\n").to_stdout
+      .to output("testball installed versions: 0.1, 0.2\n").to_stdout
       .and output(/testball does not have a version "0.3"/).to_stderr
       .and be_a_failure
   end

docs/Manpage.md

@@ -444,8 +444,8 @@ With `--verbose` or `-v`, many commands print extra debugging information. Note
 
     Exits with a non-zero status if any style violations are found.
 
-  * `switch` `name` `version`:
-    Symlink all of the specific `version` of `name`'s install to Homebrew prefix.
+  * `switch` `formula` `version`:
+    Symlink all of the specific `version` of `formula`'s install to Homebrew prefix.
 
   * `tap`:
     List all installed taps.

manpages/brew.1

@@ -455,8 +455,8 @@ Passing \fB\-\-only\-cops=\fR\fIcops\fR will check for violations of only the li
 Exits with a non\-zero status if any style violations are found\.
 .
 .TP
-\fBswitch\fR \fIname\fR \fIversion\fR
-Symlink all of the specific \fIversion\fR of \fIname\fR\'s install to Homebrew prefix\.
+\fBswitch\fR \fIformula\fR \fIversion\fR
+Symlink all of the specific \fIversion\fR of \fIformula\fR\'s install to Homebrew prefix\.
 .
 .TP
 \fBtap\fR