install: check if formula is already linked before fetching

Library/Homebrew/install.rb

@@ -209,6 +209,25 @@ module Homebrew
           Or to force-install it, run:
             brew install #{f} --force
         EOS
+      elsif f.linked?
+        message = "#{f.name} #{f.linked_version} is already installed"
+        if f.outdated? && !head
+          return true unless Homebrew::EnvConfig.no_install_upgrade?
+
+          onoe <<~EOS
+            #{message}
+            To upgrade to #{f.pkg_version}, run:
+              brew upgrade #{f.full_name}
+          EOS
+        elsif only_dependencies
+          return true
+        else
+          onoe <<~EOS
+            #{message}
+            To install #{f.pkg_version}, first run:
+              brew unlink #{f.name}
+          EOS
+        end
       else
         # If none of the above is true and the formula is linked, then
         # FormulaInstaller will handle this case.
@@ -281,42 +300,24 @@ module Homebrew
       end.compact
 
       formula_installers.each do |fi|
-        install_formula(fi, only_deps: only_deps)
+        install_formula(fi)
         Cleanup.install_formula_clean!(fi.formula)
       end
     end
 
-    def install_formula(formula_installer, only_deps: false)
+    def install_formula(formula_installer)
       f = formula_installer.formula
 
       formula_installer.prelude
 
       f.print_tap_action
 
-      if f.linked_keg.directory?
+      if f.linked? && f.outdated? && !f.head? && !Homebrew::EnvConfig.no_install_upgrade?
-        if Homebrew::EnvConfig.no_install_upgrade?
+        puts "#{f.full_name} #{f.linked_version} is installed but outdated"
-          message = <<~EOS
-            #{f.name} #{f.linked_version} is already installed
-          EOS
-          message += if f.outdated? && !f.head?
-            <<~EOS
-              To upgrade to #{f.pkg_version}, run:
-                brew upgrade #{f.full_name}
-            EOS
-          else
-            <<~EOS
-              To install #{f.pkg_version}, first run:
-                brew unlink #{f.name}
-            EOS
-          end
-          raise CannotInstallFormulaError, message unless only_deps
-        elsif f.outdated? && !f.head?
-          puts "#{f.name} #{f.linked_version} is installed but outdated"
         kegs = Upgrade.outdated_kegs(f)
         linked_kegs = kegs.select(&:linked?)
         Upgrade.print_upgrade_message(f, formula_installer.options)
       end
-      end
 
       kegs.each(&:unlink) if kegs.present?