From 8604b4b98a5fc587129ab8155c546fc45efe62ff Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Thu, 10 Sep 2020 23:01:02 +0300
Subject: Add support for default global variable overrides

---
 build2/b-options.cxx |  3 ++-
 build2/b.cli         |  3 ++-
 build2/b.cxx         | 47 +++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/build2/b-options.cxx b/build2/b-options.cxx
index 60eeec6..2bc65b3 100644
--- a/build2/b-options.cxx
+++ b/build2/b-options.cxx
@@ -1529,7 +1529,8 @@ namespace build2
        << ::std::endl
        << "The default options files for the build system driver are called \033[1mb.options\033[0m and" << ::std::endl
        << "are searched for in the \033[1m.build2/\033[0m subdirectory of the home directory and in the" << ::std::endl
-       << "system directory (for example, \033[1m/etc/build2/\033[0m) if configured." << ::std::endl
+       << "system directory (for example, \033[1m/etc/build2/\033[0m) if configured. Note that besides" << ::std::endl
+       << "options these files can also contain global variable overrides." << ::std::endl
        << ::std::endl
        << "Once the search is complete, the files are loaded in the reverse order, that" << ::std::endl
        << "is, beginning from the system directory (if any), followed by the home" << ::std::endl
diff --git a/build2/b.cli b/build2/b.cli
index 7566418..31247f9 100644
--- a/build2/b.cli
+++ b/build2/b.cli
@@ -659,7 +659,8 @@ namespace build2
   The default options files for the build system driver are called
   \cb{b.options} and are searched for in the \cb{.build2/} subdirectory of the
   home directory and in the system directory (for example, \cb{/etc/build2/})
-  if configured.
+  if configured. Note that besides options these files can also contain global
+  variable overrides.
 
   Once the search is complete, the files are loaded in the reverse order, that
   is, beginning from the system directory (if any), followed by the home
diff --git a/build2/b.cxx b/build2/b.cxx
index 4e9ebf7..66b217d 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -342,7 +342,7 @@ main (int argc, char* argv[])
         }
 
         // Merge all the individual buildspec arguments into a single string.
-        // We wse newlines to separate arguments so that line numbers in
+        // We use newlines to separate arguments so that line numbers in
         // diagnostics signify argument numbers. Clever, huh?
         //
         if (argn != 0)
@@ -381,7 +381,9 @@ main (int argc, char* argv[])
         if (ops.default_options_specified ())
           extra = ops.default_options ();
 
-        ops = merge_default_options (
+        // Load default options files.
+        //
+        default_options<options> def_ops (
           load_default_options<options,
                                cl::argv_file_scanner,
                                cl::unknown_mode> (
@@ -400,8 +402,45 @@ main (int argc, char* argv[])
                 else
                   trace << "loading " << (r ? "remote " : "local ") << f;
               }
-            }),
-          ops);
+            },
+            true /* args */));
+
+        // Merge the default and command line options.
+        //
+        ops = merge_default_options (def_ops, ops);
+
+        // Merge the default and command line global overrides.
+        //
+        // Note that the "broken down" variable assignments occupying a single
+        // line are naturally supported.
+        //
+        cmd_vars =
+          merge_default_arguments (
+            def_ops,
+            cmd_vars,
+            [] (const default_options_entry<options>& e, const strings&)
+            {
+              path_name fn (e.file);
+
+              // Verify that all arguments are global overrides.
+              //
+              for (const string& a: e.arguments)
+              {
+                size_t p (a.find ('=', 1));
+                if (p == string::npos || a[0] != '!')
+                {
+                  diag_record dr (fail (fn));
+                  dr << "expected option or global variable override instead "
+                     << "of '" << a << "'";
+
+                  if (p != string::npos)
+                    dr << info << "prefix variable assignment with '!'";
+                }
+
+                if (p == 1 || (p == 2 && a[1] == '+')) // '!=' or '!+=' ?
+                  fail (fn) << "missing variable name in '" << a << "'";
+              }
+            });
       }
       catch (const pair<path, system_error>& e)
       {
-- 
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