Add DownloadError to catch a broader range of resource download errors.

Adding a broader exception class allows for errors raised in Resource.fetch
to be caught in upgrade and prevent the process from being killed when
a download fails. This should resolve issue 18364.

Fixes Homebrew/homebrew#18364.
Closes Homebrew/homebrew#26618.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/upgrade.rb

@@ -92,6 +92,8 @@ module Homebrew extend self
     e.dump
     puts
     Homebrew.failed = true
+  rescue DownloadError => e
+    ofail e
   ensure
     # restore previous installation state if build failed
     outdated_keg.link if outdated_keg and not f.installed? rescue nil

Library/Homebrew/exceptions.rb

@@ -229,6 +229,13 @@ class CompilerSelectionError < Homebrew::InstallationError
   end
 end
 
+# Raised in Resource.fetch
+class DownloadError < RuntimeError
+  def initialize(formula)
+    super "Failed to download resource for package: #{formula}"
+  end
+end
+
 # raised in CurlDownloadStrategy.fetch
 class CurlDownloadStrategyError < RuntimeError; end
 

Library/Homebrew/resource.rb

@@ -76,10 +76,14 @@ class Resource
 
   # For brew-fetch and others.
   def fetch
-    # Ensure the cache exists
-    HOMEBREW_CACHE.mkpath
-    downloader.fetch
-    cached_download
+    begin
+      # Ensure the cache exists
+      HOMEBREW_CACHE.mkpath
+      downloader.fetch
+      cached_download
+    rescue ErrorDuringExecution, CurlDownloadStrategyError => e
+      raise DownloadError.new(downloader.name)
+    end
   end
 
   def verify_download_integrity fn