support newline between headers expression and sha256: annotation

Alternative to #12, thanks @ckumar1

Makefile

@@ -6,6 +6,7 @@ fix:
 	maintenance/fix
 
 test:
+	test/test-fix.rb
 	test/test-bump.rb
 	test/test-render.rb
 	test/test-bootstrap.rb

maintenance/fix

@@ -13,6 +13,13 @@ def run(cmd, opts={})
 	end
 end
 
+def fix_imports_in_text(contents)
+	contents.gsub(/(http[^ ]+ using) ([.\\\/~][^ \n]+)\s+(sha256:)/m) do |x|
+		match = Regexp.last_match
+		"#{match[1]} (#{match[2]}) #{match[3]}"
+	end
+end
+
 def main
 	require 'optparse'
 	actions = []
@@ -76,10 +83,7 @@ def main
 				if options[:fix_imports]
 					# workaround https://github.com/dhall-lang/dhall-haskell/issues/1672
 					contents = File.read(path)
-					fixed = contents.gsub(/(http[^ ]+ using) ([.\\\/~][^ ]+) (sha256:[^ $])/) do |x|
-						match = Regexp.last_match
-						"#{match[1]} (#{match[2]}) #{match[3]}"
-					end
+					fixed = fix_imports_in_text(contents)
 					if fixed != contents
 						File.write(path, fixed)
 					end
@@ -111,4 +115,6 @@ def main
 	end
 end
 
-main
+if $PROGRAM_NAME == __FILE__
+	main()
+end

test/test-fix.rb

@@ -0,0 +1,19 @@
+#!/usr/bin/env ruby
+require_relative 'lib/utest'
+
+load "maintenance/fix"
+
+test("fix imports") do
+	[
+		{
+			src: "https://example.com using ~/headers.dhall sha256:1234",
+			fix: "https://example.com using (~/headers.dhall) sha256:1234",
+		},
+		{
+			src: "https://example.com using ./headers.dhall\n    sha256:1234",
+			fix: "https://example.com using (./headers.dhall) sha256:1234",
+		},
+	].each do |test_case|
+		assert_equal(fix_imports_in_text(test_case.fetch(:src)), test_case.fetch(:fix))
+	end
+end