From 60c2c496357d3259c2fb29f7e2f1c3804eb5ad33 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 14 Feb 2022 11:25:04 +0200
Subject: Add parser::parse_eval() public API function

---
 libbuild2/parser.cxx | 44 ++++++++++++++++++++++++++++++++++++++++++++
 libbuild2/parser.hxx | 30 ++++++++++++++++++------------
 2 files changed, 62 insertions(+), 12 deletions(-)

diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index f42666b..9fbcd2b 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -355,6 +355,50 @@ namespace build2
     return make_pair (move (lhs), move (t));
   }
 
+  value parser::
+  parse_eval (lexer& l, scope& rs, scope& bs, pattern_mode pmode)
+  {
+    path_ = &l.name ();
+    lexer_ = &l;
+
+    root_ = &rs;
+    scope_ = &bs;
+    target_ = nullptr;
+    prerequisite_ = nullptr;
+
+    pbase_ = scope_->src_path_;
+
+    // Note that root_ may not be a project root.
+    //
+    auto_project_env penv (
+      stage_ != stage::boot && root_ != nullptr && root_->root_extra != nullptr
+      ? auto_project_env (*root_)
+      : auto_project_env ());
+
+    token t;
+    type tt;
+    next (t, tt);
+
+    if (tt != type::lparen)
+      fail (t) << "expected '(' instead of " << t;
+
+    location loc (get_location (t));
+    mode (lexer_mode::eval, '@');
+    next_with_attributes (t, tt);
+
+    values vs (parse_eval (t, tt, pmode));
+
+    if (next (t, tt) != type::eos)
+      fail (t) << "unexpected " << t;
+
+    switch (vs.size ())
+    {
+    case 0:  return value (names ());
+    case 1:  return move (vs[0]);
+    default: fail (loc) << "expected single value" << endf;
+    }
+  }
+
   bool parser::
   parse_clause (token& t, type& tt, bool one)
   {
diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index 0390e26..1474c5e 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -47,6 +47,16 @@ namespace build2
         ctx (c),
         stage_ (s) {}
 
+    // Pattern expansion mode.
+    //
+    enum class pattern_mode
+    {
+      ignore,   // Treat as literals.
+      preserve, // Preserve as name pattern.
+      expand,   // Expand to non-pattern names.
+      detect    // Implementation detail mode (see code for more information).
+    };
+
     // Issue diagnostics and throw failed in case of an error.
     //
     void
@@ -74,12 +84,18 @@ namespace build2
     parse_variable_value (lexer&, scope&, const dir_path*, const variable&);
 
     names
-    parse_export_stub (istream& is, const path_name& name, scope& r, scope& b)
+    parse_export_stub (istream& is, const path_name& name,
+                       scope& rs, scope& bs)
     {
-      parse_buildfile (is, name, &r, b);
+      parse_buildfile (is, name, &rs, bs);
       return move (export_value);
     }
 
+    // Parse an evaluation context (`(...)`).
+    //
+    value
+    parse_eval (lexer&, scope& rs, scope& bs, pattern_mode);
+
     // The above functions may be called again on the same parser instance
     // after a reset.
     //
@@ -105,16 +121,6 @@ namespace build2
   protected:
     using pattern_type = name::pattern_type;
 
-    // Pattern expansion mode.
-    //
-    enum class pattern_mode
-    {
-      ignore,   // Treat as literals.
-      preserve, // Preserve as name pattern.
-      expand,   // Expand to non-pattern names.
-      detect    // Implementation detail mode (see code for more information).
-    };
-
     // If one is true then parse a single (logical) line (logical means it
     // can actually be several lines, e.g., an if-block). Return false if
     // nothing has been parsed (i.e., we are still on the same token).
-- 
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