From cea5dd6f96f2c06467264644f800619e9d24564d Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 8 Apr 2020 13:44:33 +0200
Subject: Allow configuration variables in unnamed projects

While generally a bad idea, there are valid situations where this may happen,
such as a standalone build of the tests subproject in test-installed.
---
 libbuild2/file.cxx   | 17 +++++++++++++----
 libbuild2/parser.cxx | 36 +++++++++++++++++++++++++++---------
 2 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/libbuild2/file.cxx b/libbuild2/file.cxx
index 3e6282c..cbad9ec 100644
--- a/libbuild2/file.cxx
+++ b/libbuild2/file.cxx
@@ -1305,7 +1305,7 @@ namespace build2
     //
     if (!p.config_report.empty () && verb >= (p.config_report_new ? 2 : 3))
     {
-      const project_name& proj (named_project (root)); // Must be there.
+      const project_name& proj (named_project (root)); // Can be empty.
 
       // @@ TODO/MAYBE:
       //
@@ -1323,7 +1323,14 @@ namespace build2
       // the repetitive config.<project>. So we are only going to print the
       // part after <project> (see parser::parse_config() for details).
       //
-      string stem ('.' + proj.variable () + '.');
+      // But if there is no named project, then we print everything after
+      // config. This feels right since there could be zero identifiable
+      // information about the project in the header line. For example:
+      //
+      // config @/tmp/tests
+      //   libhello.tests.remote true
+      //
+      string stem (!proj.empty () ? '.' + proj.variable () + '.' : string ());
 
       names storage;
       for (const pair<lookup, string>& lf: p.config_report)
@@ -1342,8 +1349,10 @@ namespace build2
         }
         else
         {
-          size_t p (l.var->name.find (stem)); // Must be there.
-          n = string (l.var->name, p + stem.size ());
+          size_t p (!stem.empty ()
+                    ? l.var->name.find (stem) + stem.size ()
+                    : 7); // "config."
+          n = string (l.var->name, p);
         }
 
         dr << "\n  ";
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 797a484..e86212c 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -1690,14 +1690,29 @@ namespace build2
     // the config[.**].<project>.** pattern where <project> is the innermost
     // named project.
     //
+    // Note that we currently don't allow just the config.<project> name even
+    // though this is used quite liberally in build system modules. Allowing
+    // this will complicate the logic (and documentation) a bit and there are
+    // no obvious use-cases. On the other hand, for tools that could be used
+    // during the build (say yacc), such a variable would most likely be used
+    // to specify its location (say config.yacc) . So let's "reserve" it for
+    // now.
+    //
+    // What should we do if there is no named project? We used to fail but
+    // there are valid cases where this can happen, for example, a standalone
+    // build of an unnamed tests subproject in order to test an installed
+    // library. Doing anything fuzzy like requiring at least a four-component
+    // name in this case is probably not worth the trouble: it's possible the
+    // subproject needs some configuration values from it amalgamation (in
+    // which case it will be duplicating them in its root.build file). So
+    // for now we allow this trusting the user knows what they are doing.
+    //
     string proj;
     {
       const project_name& n (named_project (*root_));
 
-      if (n.empty ())
-        fail (t) << "configuration variable in unnamed project";
-
-      proj = n.variable ();
+      if (!n.empty ())
+        proj = n.variable ();
     }
 
     // We are now in the normal lexing mode. Since we always have <var> we
@@ -1806,13 +1821,16 @@ namespace build2
           dr << fail (t) << "configuration variable '" << name
              << "' does not start with 'config.'";
 
-        if (name.find ('.' + proj + '.') == string::npos)
-          dr << fail (t) << "configuration variable '" << name
-             << "' does not include project name";
+        if (!proj.empty ())
+        {
+          if (name.find ('.' + proj + '.') == string::npos)
+            dr << fail (t) << "configuration variable '" << name
+               << "' does not include project name";
+        }
 
         if (!dr.empty ())
-          dr << info << "expected variable name in the 'config[.**]." << proj
-             << ".**' form";
+          dr << info << "expected variable name in the 'config[.**]."
+             << (proj.empty () ? "<project>" : proj.c_str ()) << ".**' form";
       }
 
       const variable& var (
-- 
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