From 5fb9f8b808b9d235d3e30db33f8a9630edac525f Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Wed, 17 Aug 2022 14:21:55 +0300
Subject: Allow matching empty output with here-document regex without ':'
 modifier

---
 libbuild2/script/run.cxx | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/libbuild2/script/run.cxx b/libbuild2/script/run.cxx
index 8b609f1..5b45afd 100644
--- a/libbuild2/script/run.cxx
+++ b/libbuild2/script/run.cxx
@@ -759,6 +759,31 @@ namespace build2
           output_info (d, op);
         }
 
+        // Note that a here-document regex without ':' modifier can never
+        // match an empty output since it always contains the trailing empty
+        // line-char. This can be confusing, as for example while testing a
+        // program which can print some line or nothing with the following
+        // test:
+        //
+        // $* >>~%EOO%
+        //   %(
+        //   Hello, World!
+        //   %)?
+        //   EOO
+        //
+        // Note that the above line-regex contains 4 line-chars and will never
+        // match empty output.
+        //
+        // Thus, let's complete an empty output with an empty line-char for
+        // such a regex, so it may potentially match.
+        //
+        if (ls.empty ()                              &&
+            rd.type == redirect_type::here_doc_regex &&
+            rd.modifiers ().find (':') == string::npos)
+        {
+          ls += line_char (string (), regex.pool);
+        }
+
         // Match the output with the regex.
         //
         // Note that we don't distinguish between the line_regex and
-- 
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