config: better handle missing variables.

Library/Homebrew/config.rb

@@ -1,18 +1,27 @@
-unless ENV["HOMEBREW_BREW_FILE"]
-  raise "HOMEBREW_BREW_FILE was not exported! Please call bin/brew directly!"
+def get_env_or_raise(env, message = nil)
+  message ||= <<~EOS
+    don't worry, you likely hit a bug auto-updating from an old version.
+    Rerun your command, everything is up-to-date and fine now
+  EOS
+  unless ENV[env]
+    abort <<~EOS
+      Error: #{env} was not exported!\nPlease #{message.chomp}.
+    EOS
+  end
+  ENV[env]
 end
 
 # Path to `bin/brew` main executable in `HOMEBREW_PREFIX`
-HOMEBREW_BREW_FILE = Pathname.new(ENV["HOMEBREW_BREW_FILE"])
+HOMEBREW_BREW_FILE = Pathname.new(get_env_or_raise("HOMEBREW_BREW_FILE", "call bin/brew directly"))
 
 # Where we link under
-HOMEBREW_PREFIX = Pathname.new(ENV["HOMEBREW_PREFIX"])
+HOMEBREW_PREFIX = Pathname.new(get_env_or_raise("HOMEBREW_PREFIX"))
 
 # Where `.git` is found
-HOMEBREW_REPOSITORY = Pathname.new(ENV["HOMEBREW_REPOSITORY"])
+HOMEBREW_REPOSITORY = Pathname.new(get_env_or_raise("HOMEBREW_REPOSITORY"))
 
 # Where we store most of Homebrew, taps, and various metadata
-HOMEBREW_LIBRARY = Pathname.new(ENV["HOMEBREW_LIBRARY"])
+HOMEBREW_LIBRARY = Pathname.new(get_env_or_raise("HOMEBREW_LIBRARY"))
 
 # Where shim scripts for various build and SCM tools are stored
 HOMEBREW_SHIMS_PATH = HOMEBREW_LIBRARY/"Homebrew/shims"
@@ -27,20 +36,20 @@
 HOMEBREW_LOCKS = HOMEBREW_PREFIX/"var/homebrew/locks"
 
 # Where we store built products
-HOMEBREW_CELLAR = Pathname.new(ENV["HOMEBREW_CELLAR"])
+HOMEBREW_CELLAR = Pathname.new(get_env_or_raise("HOMEBREW_CELLAR"))
 
 # Where downloads (bottles, source tarballs, etc.) are cached
-HOMEBREW_CACHE = Pathname.new(ENV["HOMEBREW_CACHE"])
+HOMEBREW_CACHE = Pathname.new(get_env_or_raise("HOMEBREW_CACHE"))
 
 # Where brews installed via URL are cached
 HOMEBREW_CACHE_FORMULA = HOMEBREW_CACHE/"Formula"
 
 # Where build, postinstall, and test logs of formulae are written to
-HOMEBREW_LOGS = Pathname.new(ENV["HOMEBREW_LOGS"]).expand_path
+HOMEBREW_LOGS = Pathname.new(get_env_or_raise("HOMEBREW_LOGS")).expand_path
 
 # Must use `/tmp` instead of `TMPDIR` because long paths break Unix domain sockets
 HOMEBREW_TEMP = begin
-  tmp = Pathname.new(ENV["HOMEBREW_TEMP"])
+  tmp = Pathname.new(get_env_or_raise("HOMEBREW_TEMP"))
   tmp.mkpath unless tmp.exist?
   tmp.realpath
 end