Add $quote() function for quoting values

This can be useful if we want to pass a value on the command line, for
example, in a testscript:

$* config.cxx=$quote($recall($cxx.path) $cxx.mode, true)

3 files changed, 59 insertions, 8 deletions

diff --git a/libbuild2/functions-builtin.cxx b/libbuild2/functions-builtin.cxx
index 2acd5b4..6f1b704 100644
--- a/libbuild2/functions-builtin.cxx
+++ b/libbuild2/functions-builtin.cxx
@@ -2,9 +2,13 @@
 // copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <sstream>
+
 #include <libbuild2/function.hxx>
 #include <libbuild2/variable.hxx>
 
+using namespace std;
+
 namespace build2
 {
   // Return NULL value if an environment variable is not set, untyped value
@@ -41,6 +45,27 @@ namespace build2
     f["string"] = [](uint64_t i) {return to_string (i);};
     f["string"] = [](name n) {return to_string (n);};
 
+    // Quote a value returning its string representation. If escape is true,
+    // then also escape (with a backslash) the quote characters being added
+    // (this is useful if the result will be re-parsed, for example as a
+    // Testscript command line).
+    //
+    f["quote"] = [](value* v, optional<value> escape)
+    {
+      if (v->null)
+        return string ();
+
+      untypify (*v); // Reverse to names.
+
+      ostringstream os;
+      to_stream (os,
+                 v->as<names> (),
+                 true /* quote */,
+                 '@'  /* pair */,
+                 escape && convert<bool> (move (*escape)));
+      return os.str ();
+    };
+
     // getenv
     //
     f["getenv"] = [](string name)
diff --git a/libbuild2/name.cxx b/libbuild2/name.cxx
index 4aac32f..84e03db 100644
--- a/libbuild2/name.cxx
+++ b/libbuild2/name.cxx
@@ -60,9 +60,9 @@ namespace build2
   }
 
   ostream&
-  to_stream (ostream& os, const name& n, bool quote, char pair)
+  to_stream (ostream& os, const name& n, bool quote, char pair, bool escape)
   {
-    auto write_string = [quote, pair, &os](const string& v)
+    auto write_string = [quote, pair, escape, &os](const string& v)
     {
       char sc[] = {
         '{', '}', '[', ']', '$', '(', ')', // Token endings.
@@ -78,6 +78,7 @@ namespace build2
         // Quote the string with the double quotes rather than with the single
         // one. Escape some of the special characters.
         //
+        if (escape) os << '\\';
         os << '"';
 
         for (auto c: v)
@@ -88,10 +89,19 @@ namespace build2
           os << c;
         }
 
+        if (escape) os << '\\';
         os << '"';
       }
       else if (quote && v.find_first_of (sc) != string::npos)
-        os << "'" << v << "'";
+      {
+        if (escape) os << '\\';
+        os << '\'';
+
+        os << v;
+
+        if (escape) os << '\\';
+        os << '\'';
+      }
       else
         os << v;
     };
@@ -115,7 +125,7 @@ namespace build2
     // If quoted then print empty name as '' rather than {}.
     //
     if (quote && n.empty ())
-      return os << "''";
+      return os << (escape ? "\\'\\'" : "''");
 
     if (n.proj)
     {
@@ -168,13 +178,17 @@ namespace build2
   }
 
   ostream&
-  to_stream (ostream& os, const names_view& ns, bool quote, char pair)
+  to_stream (ostream& os,
+             const names_view& ns,
+             bool quote,
+             char pair,
+             bool escape)
   {
     for (auto i (ns.begin ()), e (ns.end ()); i != e; )
     {
       const name& n (*i);
       ++i;
-      to_stream (os, n, quote, pair);
+      to_stream (os, n, quote, pair, escape);
 
       if (n.pair)
         os << n.pair;
diff --git a/libbuild2/name.hxx b/libbuild2/name.hxx
index 1ce073a..738645d 100644
--- a/libbuild2/name.hxx
+++ b/libbuild2/name.hxx
@@ -129,11 +129,19 @@ namespace build2
   //
   // \$("
   //
+  // If escape is true, then escape (with a backslash) the quote characters
+  // being added (this is useful if the result will be re-parsed, for example
+  // as a Testscript command line).
+  //
   // Note that in the quoted mode empty unqualified name is printed as '',
   // not {}.
   //
   LIBBUILD2_SYMEXPORT ostream&
-  to_stream (ostream&, const name&, bool quote, char pair = '\0');
+  to_stream (ostream&,
+             const name&,
+             bool quote,
+             char pair = '\0',
+             bool escape = false);
 
   inline ostream&
   operator<< (ostream& os, const name& n) {return to_stream (os, n, false);}
@@ -153,7 +161,11 @@ namespace build2
   // The same semantics as to_stream(name).
   //
   LIBBUILD2_SYMEXPORT ostream&
-  to_stream (ostream&, const names_view&, bool quote, char pair = '\0');
+  to_stream (ostream&,
+             const names_view&,
+             bool quote,
+             char pair = '\0',
+             bool escape = false);
 
   inline ostream&
   operator<< (ostream& os, const names_view& ns) {