Refer to default branch in links with HEAD

Anywhere we can use `blob/master` we can use `blob/HEAD` instead. This
will make life easier if we ever rename our default branch in future
(once/if Git and GitHub provides the necessary tooling to do so).

Author: MikeMcQuaid

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
-- [ ] Have you followed the guidelines in our [Contributing](https://github.com/Homebrew/brew/blob/master/CONTRIBUTING.md) document?
+- [ ] Have you followed the guidelines in our [Contributing](https://github.com/Homebrew/brew/blob/HEAD/CONTRIBUTING.md) document?
 - [ ] Have you checked to ensure there aren't other open [Pull Requests](https://github.com/Homebrew/brew/pulls) for the same change?
 - [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
-- [ ] Have you written new tests for your changes? [Here's an example](https://github.com/Homebrew/brew/blob/master/Library/Homebrew/test/PATH_spec.rb).
+- [ ] Have you written new tests for your changes? [Here's an example](https://github.com/Homebrew/brew/blob/HEAD/Library/Homebrew/test/PATH_spec.rb).
 - [ ] Have you successfully run `brew style` with your changes locally?
 - [ ] Have you successfully run `brew tests` with your changes locally?
 

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing to Homebrew
 
-First time contributing to Homebrew? Read our [Code of Conduct](https://github.com/Homebrew/.github/blob/master/CODE_OF_CONDUCT.md#code-of-conduct) and review [How To Open a Homebrew Pull Request](https://docs.brew.sh/How-To-Open-a-Homebrew-Pull-Request).
+First time contributing to Homebrew? Read our [Code of Conduct](https://github.com/Homebrew/.github/blob/HEAD/CODE_OF_CONDUCT.md#code-of-conduct) and review [How To Open a Homebrew Pull Request](https://docs.brew.sh/How-To-Open-a-Homebrew-Pull-Request).
 
 ### Report a bug
 

Library/.rubocop_cask.yml

@@ -1,7 +1,7 @@
 inherit_from: ./.rubocop_shared.yml
 
 Cask/HomepageMatchesUrl:
-  Description: 'Ensure that the homepage and url match, otherwise add a comment. More info at https://github.com/Homebrew/homebrew-cask/blob/master/doc/cask_language_reference/stanzas/url.md#when-url-and-homepage-hostnames-differ-add-a-comment'
+  Description: 'Ensure that the homepage and url match, otherwise add a comment. More info at https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/cask_language_reference/stanzas/url.md#when-url-and-homepage-hostnames-differ-add-a-comment'
   Enabled: true
   Exclude:
   - '**/test/support/fixtures/cask/Casks/**/*.rb'
@@ -15,11 +15,11 @@ Cask/NoDslVersion:
   Enabled: true
 
 Cask/StanzaGrouping:
-  Description: 'Ensure that cask stanzas are grouped correctly. More info at https://github.com/Homebrew/homebrew-cask/blob/master/CONTRIBUTING.md#stanza-order'
+  Description: 'Ensure that cask stanzas are grouped correctly. More info at https://github.com/Homebrew/homebrew-cask/blob/HEAD/CONTRIBUTING.md#stanza-order'
   Enabled: true
 
 Cask/StanzaOrder:
-  Description: 'Ensure that cask stanzas are sorted correctly. More info at https://github.com/Homebrew/homebrew-cask/blob/master/CONTRIBUTING.md#stanza-order'
+  Description: 'Ensure that cask stanzas are sorted correctly. More info at https://github.com/Homebrew/homebrew-cask/blob/HEAD/CONTRIBUTING.md#stanza-order'
   Enabled: true
 
 Layout/HashAlignment:

Library/Homebrew/cask/audit.rb

@@ -219,7 +219,7 @@ def check_latest_with_auto_updates
     def check_hosting_with_appcast
       return if cask.appcast
 
-      add_appcast = "please add an appcast. See https://github.com/Homebrew/homebrew-cask/blob/master/doc/cask_language_reference/stanzas/appcast.md"
+      add_appcast = "please add an appcast. See https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/cask_language_reference/stanzas/appcast.md"
 
       case cask.url.to_s
       when %r{github.com/([^/]+)/([^/]+)/releases/download/(\S+)}
@@ -246,9 +246,9 @@ def check_url
     def check_download_url_format
       odebug "Auditing URL format"
       if bad_sourceforge_url?
-        add_warning "SourceForge URL format incorrect. See https://github.com/Homebrew/homebrew-cask/blob/master/doc/cask_language_reference/stanzas/url.md#sourceforgeosdn-urls"
+        add_warning "SourceForge URL format incorrect. See https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/cask_language_reference/stanzas/url.md#sourceforgeosdn-urls"
       elsif bad_osdn_url?
-        add_warning "OSDN URL format incorrect. See https://github.com/Homebrew/homebrew-cask/blob/master/doc/cask_language_reference/stanzas/url.md#sourceforgeosdn-urls"
+        add_warning "OSDN URL format incorrect. See https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/cask_language_reference/stanzas/url.md#sourceforgeosdn-urls"
       end
     end
 
@@ -355,7 +355,7 @@ def core_formula_names
     end
 
     def core_formula_url
-      "#{core_tap.default_remote}/blob/master/Formula/#{cask.token}.rb"
+      "#{core_tap.default_remote}/blob/HEAD/Formula/#{cask.token}.rb"
     end
 
     def check_download

Library/Homebrew/cask/cmd/info.rb

@@ -97,7 +97,7 @@ def self.repo_info(cask)
         url = if cask.tap.custom_remote? && !cask.tap.remote.nil?
           cask.tap.remote
         else
-          "#{cask.tap.default_remote}/blob/master/Casks/#{cask.token}.rb"
+          "#{cask.tap.default_remote}/blob/HEAD/Casks/#{cask.token}.rb"
         end
 
         "From: #{Formatter.url(url)}"

Library/Homebrew/cask/exceptions.rb

@@ -151,7 +151,7 @@ def to_s
             File: #{path}
         To retry an incomplete download, remove the file above.
         If the issue persists, visit:
-          #{Formatter.url("https://github.com/Homebrew/homebrew-cask/blob/master/doc/reporting_bugs/checksum_does_not_match_error.md")}
+          #{Formatter.url("https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/reporting_bugs/checksum_does_not_match_error.md")}
       EOS
     end
   end

Library/Homebrew/cmd/info.rb

@@ -140,7 +140,7 @@ def print_json
 
   def github_remote_path(remote, path)
     if remote =~ %r{^(?:https?://|git(?:@|://))github\.com[:/](.+)/(.+?)(?:\.git)?$}
-      "https://github.com/#{Regexp.last_match(1)}/#{Regexp.last_match(2)}/blob/master/#{path}"
+      "https://github.com/#{Regexp.last_match(1)}/#{Regexp.last_match(2)}/blob/HEAD/#{path}"
     else
       "#{remote}/#{path}"
     end

Library/Homebrew/extend/os/linux/hardware/cpu.rb

@@ -21,7 +21,7 @@ def family
         return :dunno unless intel?
 
         # See https://software.intel.com/en-us/articles/intel-architecture-and-processor-identification-with-cpuid-model-and-family-numbers
-        # and https://github.com/llvm-mirror/llvm/blob/master/lib/Support/Host.cpp
+        # and https://github.com/llvm-mirror/llvm/blob/HEAD/lib/Support/Host.cpp
         # and https://en.wikipedia.org/wiki/List_of_Intel_CPU_microarchitectures#Roadmap
         cpu_family = cpuinfo[/^cpu family\s*: ([0-9]+)/, 1].to_i
         cpu_model = cpuinfo[/^model\s*: ([0-9]+)/, 1].to_i

Library/Homebrew/keg.rb

@@ -80,7 +80,7 @@ def to_s
   ).map { |dir| HOMEBREW_PREFIX/dir }.sort.uniq.freeze
 
   # Keep relatively in sync with
-  # https://github.com/Homebrew/install/blob/master/install
+  # https://github.com/Homebrew/install/blob/HEAD/install
   MUST_EXIST_DIRECTORIES = (MUST_EXIST_SUBDIRECTORIES + [
     HOMEBREW_CELLAR,
   ].sort.uniq).freeze

Library/Homebrew/os/mac.rb

@@ -43,14 +43,14 @@ def latest_sdk_version
     def latest_stable_version
       # TODO: bump version when new macOS is released and also update
       # references in docs/Installation.md and
-      # https://github.com/Homebrew/install/blob/master/install
+      # https://github.com/Homebrew/install/blob/HEAD/install
       Version.new "10.15"
     end
 
     def outdated_release?
       # TODO: bump version when new macOS is released and also update
       # references in docs/Installation.md and
-      # https://github.com/Homebrew/install/blob/master/install
+      # https://github.com/Homebrew/install/blob/HEAD/install
       version < "10.13"
     end