From 28d1791e2dc66cc610468deb29ea030e28d0793c Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Fri, 13 Sep 2019 20:47:58 +0300
Subject: Add support for testscript builtin escaping

---
 doc/testscript.cli                       |  7 +++++++
 libbuild2/test/script/runner.cxx         | 27 +++++++++++++++++++++++----
 tests/test/script/runner/expr.testscript | 20 ++++++++++++++++++++
 3 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/doc/testscript.cli b/doc/testscript.cli
index 8b9509d..f51bf14 100644
--- a/doc/testscript.cli
+++ b/doc/testscript.cli
@@ -2232,6 +2232,13 @@ in option handling) and extensions, as described in this chapter. Note also
 that the builtins are implemented in-process with some of the simple ones
 such as \c{true/false}, \c{mkdir}, etc., being just function calls.
 
+To run a system utility instead of a builtin prefix its name with \c{^}, for
+example:
+
+\
+^cat --squeeze-blank <file>
+\
+
 
 \h#builtins-cat|\c{cat}|
 
diff --git a/libbuild2/test/script/runner.cxx b/libbuild2/test/script/runner.cxx
index 630d4c2..554edd0 100644
--- a/libbuild2/test/script/runner.cxx
+++ b/libbuild2/test/script/runner.cxx
@@ -1865,7 +1865,9 @@ namespace build2
 
           // Resolve the relative not simple program path against the scope's
           // working directory. The simple one will be left for the process
-          // path search machinery.
+          // path search machinery. Also strip the potential leading `^`,
+          // indicating that this is an external program rather than a
+          // builtin.
           //
           path p;
 
@@ -1873,10 +1875,25 @@ namespace build2
           {
             p = path (args[0]);
 
-            if (p.relative () && !p.simple ())
+            if (p.relative ())
             {
-              p = sp.wd_path / p;
-              args[0] = p.string ().c_str ();
+              auto program = [&p, &args] (path pp)
+              {
+                p = move (pp);
+                args[0] = p.string ().c_str ();
+              };
+
+              if (p.simple ())
+              {
+                const string& s (p.string ());
+
+                // Don't end up with an empty path.
+                //
+                if (s.size () > 1 && s[0] == '^')
+                  program (path (s, 1, s.size () - 1));
+              }
+              else
+                program (sp.wd_path / p);
             }
           }
           catch (const invalid_path& e)
@@ -1888,6 +1905,8 @@ namespace build2
           {
             process_path pp (process::path_search (args[0]));
 
+            // Note: the builtin-escaping character '^' is not printed.
+            //
             if (verb >= 2)
               print_process (args);
 
diff --git a/tests/test/script/runner/expr.testscript b/tests/test/script/runner/expr.testscript
index fd9c643..56747a4 100644
--- a/tests/test/script/runner/expr.testscript
+++ b/tests/test/script/runner/expr.testscript
@@ -522,3 +522,23 @@
     info: test id: 1
   EOE
 }
+
+: escape-builtin
+:
+if ($cxx.target.class == 'linux')
+{
+  $c <<EOI && $b
+    cat <<EOF >=f;
+      x
+
+
+      y
+      EOF
+
+    ^cat --squeeze-blank f >>EOO
+      x
+
+      y
+      EOO
+    EOI
+}
-- 
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