From 0ce923f1b9b008cf44602255f935bf3d9c4ba90d Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 13 Jul 2020 13:24:07 +0200
Subject: Reserve backtick (`) and bit-or (|) in eval context for future use

Specifically, they are reserved for future support of arithmetic evaluation
contexts and evaluation pipelines, respectively.
---
 doc/manual.cli                       | 6 +++++-
 libbuild2/lexer+eval.test.testscript | 4 +++-
 libbuild2/lexer.cxx                  | 8 +++++---
 libbuild2/parser.cxx                 | 8 ++++++++
 libbuild2/token.cxx                  | 3 +++
 libbuild2/token.hxx                  | 1 +
 6 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/doc/manual.cli b/doc/manual.cli
index f6039d6..cb6c1ec 100644
--- a/doc/manual.cli
+++ b/doc/manual.cli
@@ -3465,7 +3465,11 @@ Note that \c{?:} (ternary operator) and \c{!} (logical not) are
 right-associative. Unlike C++, all the comparison operators have the same
 precedence. A qualified name cannot be combined with any other operator
 (including ternary) unless enclosed in parentheses. The \c{eval} option in the
-\c{eval-value} production shall contain a single value only (no commas).|
+\c{eval-value} production shall contain a single value only (no commas).
+
+Additionally, the \c{`} (backtick) and \c{|} (bitwise or) tokens are reserved
+for future support of arithmetic evaluation contexts and evaluation pipelines,
+respectively.|
 
 A function call starts with \c{$} followed by its name and an eval context
 listing its arguments. Note that there is no space between the name and
diff --git a/libbuild2/lexer+eval.test.testscript b/libbuild2/lexer+eval.test.testscript
index 75c8fce..53c5923 100644
--- a/libbuild2/lexer+eval.test.testscript
+++ b/libbuild2/lexer+eval.test.testscript
@@ -27,7 +27,9 @@ EOO
 : logical
 :
 $* <:'x|x||x&x&&x!x!!x)' >>EOO
-'x|x'
+'x'
+|
+'x'
 ||
 'x&x'
 &&
diff --git a/libbuild2/lexer.cxx b/libbuild2/lexer.cxx
index ff7be02..9b7d01e 100644
--- a/libbuild2/lexer.cxx
+++ b/libbuild2/lexer.cxx
@@ -120,8 +120,8 @@ namespace build2
         // NOTE: remember to update special() lambda in parse_names() if
         //       adding any new single-character tokens to the eval mode.
         //
-        s1 = ":<>=!&|?, $(){}#\t\n";
-        s2 = "   = &|           ";
+        s1 = ":<>=!&|?,` $(){}#\t\n";
+        s2 = "   = &             ";
         break;
       }
     case lexer_mode::buildspec:
@@ -478,6 +478,7 @@ namespace build2
     case '$': return make_token (type::dollar);
     case '?': return make_token (type::question);
     case ',': return make_token (type::comma);
+    case '`': return make_token (type::backtick);
     case '(': return make_token (type::lparen);
     case ')':
       {
@@ -498,7 +499,7 @@ namespace build2
         type r (type::eos);
         switch (c)
         {
-        case '|': if (p == '|') r = type::log_or; break;
+        case '|': r = (p == '|' ? type::log_or : type::bit_or); break;
         case '&': if (p == '&') r = type::log_and; break;
 
         case '<': r = (p == '=' ? type::less_equal : type::less); break;
@@ -514,6 +515,7 @@ namespace build2
 
         switch (r)
         {
+        case type::bit_or:
         case type::less:
         case type::greater:
         case type::log_not: break;
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 2255947..711c5f0 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -4038,6 +4038,12 @@ namespace build2
 
     values r (parse_eval_comma (t, tt, pmode, true));
 
+    if (tt == type::backtick) // @@ TMP
+      fail (t) << "arithmetic evaluation context not yet supported";
+
+    if (tt == type::bit_or) // @@ TMP
+      fail (t) << "evaluation pipeline not yet supported";
+
     if (tt != type::rparen)
       fail (t) << "unexpected " << t; // E.g., stray ':'.
 
@@ -5862,6 +5868,8 @@ namespace build2
               case type::dollar:         r = '$';        break;
               case type::question:       r = '?';        break;
               case type::comma:          r = ',';        break;
+              case type::backtick:       r = '`';        break;
+              case type::bit_or:         r = '|';        break;
               case type::log_not:        r = '!';        break;
               case type::lparen:         r = '(';        break;
               case type::rparen:         r = ')';        break;
diff --git a/libbuild2/token.cxx b/libbuild2/token.cxx
index 7ce85be..ab14388 100644
--- a/libbuild2/token.cxx
+++ b/libbuild2/token.cxx
@@ -53,6 +53,7 @@ namespace build2
     case token_type::question:       os << q << '?'     << q; break;
     case token_type::percent:        os << q << '%'     << q; break;
     case token_type::comma:          os << q << ','     << q; break;
+    case token_type::backtick:       os << q << '`'     << q; break;
 
     case token_type::lparen:         os << q << '('     << q; break;
     case token_type::rparen:         os << q << ')'     << q; break;
@@ -81,6 +82,8 @@ namespace build2
     case token_type::less_equal:     os << q << "<="    << q; break;
     case token_type::greater_equal:  os << q << ">="    << q; break;
 
+    case token_type::bit_or:         os << q << '|'     << q; break;
+
     case token_type::log_or:         os << q << "||"    << q; break;
     case token_type::log_and:        os << q << "&&"    << q; break;
     case token_type::log_not:        os << q << '!'     << q; break;
diff --git a/libbuild2/token.hxx b/libbuild2/token.hxx
index 7344ecd..030ab48 100644
--- a/libbuild2/token.hxx
+++ b/libbuild2/token.hxx
@@ -37,6 +37,7 @@ namespace build2
       question,        // ?
       percent,         // %
       comma,           // ,
+      backtick,        // `
 
       lparen,          // (
       rparen,          // )
-- 
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