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).

.github/PULL_REQUEST_TEMPLATE.md

-- [ ] 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

 # 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

 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 @@ module Cask
     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 @@ module Cask
     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 @@ module Cask
     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 @@ module 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 @@ module Cask
             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 @@ module Homebrew
 
   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 @@ module Hardware
         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 @@ class Keg
   ).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 @@ module OS
     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
 

Library/Homebrew/rubocops/cask/homepage_matches_url.rb

@@ -14,7 +14,7 @@ module RuboCop
         include CaskHelp
 
         REFERENCE_URL =
-          "https://github.com/Homebrew/homebrew-cask/blob/master/doc/" \
+          "https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/" \
           "cask_language_reference/stanzas/url.md#when-url-and-homepage-hostnames-differ-add-a-comment"
 
         COMMENT_FORMAT = /# [^ ]+ was verified as official when first introduced to the cask/.freeze

Library/Homebrew/rubocops/cask/stanza_grouping.rb

@@ -6,7 +6,7 @@ module RuboCop
   module Cop
     module Cask
       # This cop checks that a cask's stanzas are grouped correctly.
-      # See https://github.com/Homebrew/homebrew-cask/blob/master/CONTRIBUTING.md#stanza-order
+      # See https://github.com/Homebrew/homebrew-cask/blob/HEAD/CONTRIBUTING.md#stanza-order
       # for more info.
       class StanzaGrouping < Cop
         extend Forwardable

Library/Homebrew/rubocops/cask/stanza_order.rb

@@ -6,7 +6,7 @@ module RuboCop
   module Cop
     module Cask
       # This cop checks that a cask's stanzas are ordered correctly.
-      # See https://github.com/Homebrew/homebrew-cask/blob/master/CONTRIBUTING.md#stanza-order
+      # See https://github.com/Homebrew/homebrew-cask/blob/HEAD/CONTRIBUTING.md#stanza-order
       # for more info.
       class StanzaOrder < Cop
         extend Forwardable

Library/Homebrew/test/cask/cmd/info_spec.rb

@@ -15,7 +15,7 @@ describe Cask::Cmd::Info, :cask do
       local-caffeine: 1.2.3
       https://brew.sh/
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/local-caffeine.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/local-caffeine.rb
       ==> Name
       None
       ==> Artifacts
@@ -30,7 +30,7 @@ describe Cask::Cmd::Info, :cask do
       with-auto-updates: 1.0 (auto_updates)
       https://brew.sh/autoupdates
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/with-auto-updates.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/with-auto-updates.rb
       ==> Name
       AutoUpdates
       ==> Artifacts
@@ -44,7 +44,7 @@ describe Cask::Cmd::Info, :cask do
         local-caffeine: 1.2.3
         https://brew.sh/
         Not installed
-        From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/local-caffeine.rb
+        From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/local-caffeine.rb
         ==> Name
         None
         ==> Artifacts
@@ -53,7 +53,7 @@ describe Cask::Cmd::Info, :cask do
         local-transmission: 2.61
         https://brew.sh/
         Not installed
-        From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/local-transmission.rb
+        From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/local-transmission.rb
         ==> Name
         Transmission
         ==> Artifacts
@@ -75,7 +75,7 @@ describe Cask::Cmd::Info, :cask do
       with-caveats: 1.2.3
       https://brew.sh/
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/with-caveats.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/with-caveats.rb
       ==> Name
       None
       ==> Artifacts
@@ -100,7 +100,7 @@ describe Cask::Cmd::Info, :cask do
       with-conditional-caveats: 1.2.3
       https://brew.sh/
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/with-conditional-caveats.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/with-conditional-caveats.rb
       ==> Name
       None
       ==> Artifacts
@@ -115,7 +115,7 @@ describe Cask::Cmd::Info, :cask do
       with-languages: 1.2.3
       https://brew.sh/
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/with-languages.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/with-languages.rb
       ==> Name
       None
       ==> Languages
@@ -132,7 +132,7 @@ describe Cask::Cmd::Info, :cask do
       without-languages: 1.2.3
       https://brew.sh/
       Not installed
-      From: https://github.com/Homebrew/homebrew-cask/blob/master/Casks/without-languages.rb
+      From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/without-languages.rb
       ==> Name
       None
       ==> Artifacts

Library/Homebrew/test/cmd/info_spec.rb

@@ -24,13 +24,13 @@ describe Homebrew do
 
   specify "::github_remote_path" do
     expect(subject.github_remote_path(remote, "Formula/git.rb"))
-      .to eq("https://github.com/Homebrew/homebrew-core/blob/master/Formula/git.rb")
+      .to eq("https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/git.rb")
 
     expect(subject.github_remote_path("#{remote}.git", "Formula/git.rb"))
-      .to eq("https://github.com/Homebrew/homebrew-core/blob/master/Formula/git.rb")
+      .to eq("https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/git.rb")
 
     expect(subject.github_remote_path("git@github.com:user/repo", "foo.rb"))
-      .to eq("https://github.com/user/repo/blob/master/foo.rb")
+      .to eq("https://github.com/user/repo/blob/HEAD/foo.rb")
 
     expect(subject.github_remote_path("https://mywebsite.com", "foo/bar.rb"))
       .to eq("https://mywebsite.com/foo/bar.rb")

Library/Homebrew/test/rubocops/cask/homepage_matches_url_spec.rb

@@ -110,7 +110,7 @@ describe RuboCop::Cop::Cask::HomepageMatchesUrl do
         [{
           message:  "`# brew.sh was verified as official` does not " \
                    "match the expected comment format. For details, see " \
-                  "https://github.com/Homebrew/homebrew-cask/blob/master/doc/" \
+                  "https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/" \
                   "cask_language_reference/stanzas/url.md#when-url-and-homepage-hostnames-differ-add-a-comment",
           severity: :convention,
           line:     2,
@@ -188,7 +188,7 @@ describe RuboCop::Cop::Cask::HomepageMatchesUrl do
         [{
           message:  "`brew.sh` does not match `example.org`, a comment " \
                    "has to be added above the `url` stanza. For details, see " \
-                   "https://github.com/Homebrew/homebrew-cask/blob/master/doc/" \
+                   "https://github.com/Homebrew/homebrew-cask/blob/HEAD/doc/" \
                    "cask_language_reference/stanzas/url.md#when-url-and-homepage-hostnames-differ-add-a-comment",
           severity: :convention,
           line:     2,

README.md

@@ -19,7 +19,7 @@ Second, read the [Troubleshooting Checklist](https://docs.brew.sh/Troubleshootin
 **If you don't read these it will take us far longer to help you with your problem.**
 
 ## Contributing
-We'd love you to contribute to Homebrew. First, please read our [Contribution Guide](CONTRIBUTING.md) and [Code of Conduct](https://github.com/Homebrew/.github/blob/master/CODE_OF_CONDUCT.md#code-of-conduct).
+We'd love you to contribute to Homebrew. First, please read our [Contribution Guide](CONTRIBUTING.md) and [Code of Conduct](https://github.com/Homebrew/.github/blob/HEAD/CODE_OF_CONDUCT.md#code-of-conduct).
 
 We explicitly welcome contributions from people who have never contributed to open-source before: we were all beginners once! We can help build on a partially working pull request with the aim of getting it merged. We are also actively seeking to diversify our contributors and especially welcome contributions from women from all backgrounds and people of colour.
 

docs/Analytics.md

@@ -45,7 +45,7 @@ Homebrew's analytics are sent throughout Homebrew's execution to Google Analytic
 Summaries of installation and error analytics are publicly available [here](https://brew.sh/analytics/). A JSON API is also available.
 
 ## How?
-The code is viewable in [`analytics.rb`](https://github.com/Homebrew/brew/blob/master/Library/Homebrew/utils/analytics.rb) and [`analytics.sh`](https://github.com/Homebrew/brew/blob/master/Library/Homebrew/utils/analytics.sh). They are done in a separate background process and fail fast to avoid delaying any execution. They will fail immediately and silently if you have no network connection.
+The code is viewable in [`analytics.rb`](https://github.com/Homebrew/brew/blob/HEAD/Library/Homebrew/utils/analytics.rb) and [`analytics.sh`](https://github.com/Homebrew/brew/blob/HEAD/Library/Homebrew/utils/analytics.sh). They are done in a separate background process and fail fast to avoid delaying any execution. They will fail immediately and silently if you have no network connection.
 
 ## Opting out
 Homebrew analytics helps us maintainers and leaving it on is appreciated. However, if you want to opt out of Homebrew's analytics, you can set this variable in your environment:

docs/External-Commands.md

@@ -39,7 +39,7 @@ For example, see the [header of `brew-services.rb`](https://github.com/Homebrew/
 
 ### homebrew-livecheck
 Check if there is a new upstream version of a formula.
-See the [`README`](https://github.com/Homebrew/homebrew-livecheck/blob/master/README.md) for more info and usage.
+See the [`README`](https://github.com/Homebrew/homebrew-livecheck/blob/HEAD/README.md) for more info and usage.
 
 Install using:
 
@@ -49,7 +49,7 @@ brew tap homebrew/livecheck
 
 ### homebrew-command-not-found
 Ubuntu's `command-not-found equivalent` for Homebrew.
-See the [`README`](https://github.com/Homebrew/homebrew-command-not-found/blob/master/README.md) for more info and usage.
+See the [`README`](https://github.com/Homebrew/homebrew-command-not-found/blob/HEAD/README.md) for more info and usage.
 
 Install using:
 
@@ -59,7 +59,7 @@ brew tap homebrew/command-not-found
 
 ### homebrew-aliases
 Allows you to alias your Homebrew commands.
-See the [`README`](https://github.com/Homebrew/homebrew-aliases/blob/master/README.md) for more info and usage.
+See the [`README`](https://github.com/Homebrew/homebrew-aliases/blob/HEAD/README.md) for more info and usage.
 
 Install using:
 

docs/FAQ.md

@@ -74,7 +74,7 @@ the launchctl PATH for *all users*. For earlier versions of macOS, see
 [this page](https://developer.apple.com/legacy/library/qa/qa1067/_index.html).
 
 ## How do I contribute to Homebrew?
-Read our [contribution guidelines](https://github.com/Homebrew/brew/blob/master/CONTRIBUTING.md#contributing-to-homebrew).
+Read our [contribution guidelines](https://github.com/Homebrew/brew/blob/HEAD/CONTRIBUTING.md#contributing-to-homebrew).
 
 ## Why do you compile everything?
 Homebrew provides pre-compiled versions for many formulae. These