Don't switch projects when switching scopes during bootstrap

5 files changed, 47 insertions, 30 deletions

diff --git a/libbuild2/config/init.cxx b/libbuild2/config/init.cxx
index f0f4841..aa2c763 100644
--- a/libbuild2/config/init.cxx
+++ b/libbuild2/config/init.cxx
@@ -215,7 +215,10 @@ namespace build2
             info << "consider reconfiguring " << project (rs) << '@'
                    << rs.out_path ();
 
-        source (rs, rs, lex);
+        // Treat it as continuation of bootstrap to avoid project switching
+        // (see switch_scope() for details).
+        //
+        source (rs, rs, lex, load_stage::boot);
       };
 
       auto load_config_file = [&load_config] (const path& f, const location& l)
diff --git a/libbuild2/file.cxx b/libbuild2/file.cxx
index cbad9ec..0bf3fd4 100644
--- a/libbuild2/file.cxx
+++ b/libbuild2/file.cxx
@@ -239,9 +239,9 @@ namespace build2
   }
 
   void
-  source (scope& root, scope& base, lexer& l)
+  source (scope& root, scope& base, lexer& l, load_stage s)
   {
-    parser p (root.ctx);
+    parser p (root.ctx, s);
     source (p, root, base, l);
   }
 
@@ -412,16 +412,17 @@ namespace build2
   }
 
   pair<scope&, scope*>
-  switch_scope (scope& root, const dir_path& p)
+  switch_scope (scope& root, const dir_path& p, bool proj)
   {
     // First, enter the scope into the map and see if it is in any project. If
     // it is not, then there is nothing else to do.
     //
     auto i (root.ctx.scopes.rw (root).insert (p));
     scope& base (i->second);
-    scope* rs (base.root_scope ());
 
-    if (rs != nullptr)
+    scope* rs (nullptr);
+
+    if (proj && (rs = base.root_scope ()) != nullptr)
     {
       // Path p can be src_base or out_base. Figure out which one it is.
       //
@@ -536,7 +537,8 @@ namespace build2
     //   prevent multiple sourcing. We handle it here but we still need
     //   something like source_once (once [scope] source) in buildfiles.
     //
-    source_once (root, root, f);
+    parser p (root.ctx, load_stage::boot);
+    source_once (p, root, root, f, root);
   }
 
   pair<value, bool>
@@ -814,7 +816,7 @@ namespace build2
         //
         if (rs.buildfiles.insert (f).second)
         {
-          parser p (rs.ctx, parser::stage::boot);
+          parser p (rs.ctx, load_stage::boot);
           source (p, rs, rs, f);
         }
         else
@@ -1047,7 +1049,7 @@ namespace build2
       if (root.root_extra == nullptr)
         setup_root_extra (root, altn);
 
-      parser p (root.ctx, parser::stage::boot);
+      parser p (root.ctx, load_stage::boot);
       source_hooks (p, root, d, true /* pre */);
     }
   }
@@ -1061,7 +1063,7 @@ namespace build2
 
     if (exists (d))
     {
-      parser p (root.ctx, parser::stage::boot);
+      parser p (root.ctx, load_stage::boot);
       source_hooks (p, root, d, false /* pre */);
     }
   }
@@ -1294,7 +1296,7 @@ namespace build2
 
     // Reuse the parser to accumulate the configuration variable information.
     //
-    parser p (root.ctx, parser::stage::root);
+    parser p (root.ctx, load_stage::root);
 
     if (he) {source_hooks (p, root, hd, true  /* pre */); p.reset ();}
     if (fe) {source_once (p, root, root, f, root);}
diff --git a/libbuild2/file.hxx b/libbuild2/file.hxx
index 2ca72b1..b44efb6 100644
--- a/libbuild2/file.hxx
+++ b/libbuild2/file.hxx
@@ -67,6 +67,15 @@ namespace build2
   LIBBUILD2_SYMEXPORT pair<dir_path, bool>
   find_out_root (const dir_path&, optional<bool>& altn);
 
+  // Project's loading stage during which the parsing is performed.
+  //
+  enum class load_stage
+  {
+    boot,  // Loading bootstrap.build (or bootstrap pre/post hooks).
+    root,  // Loading root.build (or root pre/post hooks).
+    rest   // Loading the rest (ordinary buildfiles, command line, etc).
+  };
+
   // If buildfile is '-', then read from STDIN.
   //
   LIBBUILD2_SYMEXPORT void
@@ -82,7 +91,7 @@ namespace build2
   // stdin that requires parse_variable()).
   //
   LIBBUILD2_SYMEXPORT void
-  source (scope& root, scope& base, lexer&);
+  source (scope& root, scope& base, lexer&, load_stage = load_stage::rest);
 
   // As above but first check if this buildfile has already been sourced for
   // the base scope. Return false if the file has already been sourced.
@@ -115,13 +124,14 @@ namespace build2
               const dir_path& out_base,
               const dir_path& src_base);
 
-  // Return a scope for the specified directory (first). Note that switching
-  // to this scope might also involve switch to a new root scope (second) if
-  // the new scope is in another project. If the new scope is not in any
-  // project, then NULL is returned in second.
+  // Return a scope for the specified directory (first). If project is true
+  // then switching to this scope might also involve switch to a new root
+  // scope (second) if the new scope is in another project. If project is
+  // false or the new scope is not in any project, then NULL is returned in
+  // second.
   //
   LIBBUILD2_SYMEXPORT pair<scope&, scope*>
-  switch_scope (scope& root, const dir_path&);
+  switch_scope (scope& root, const dir_path&, bool project = true);
 
   // Bootstrap and optionally load an ad hoc (sub)project (i.e., the kind that
   // is not discovered and loaded automatically by bootstrap/load functions
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index e3f9605..cd6fe5e 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -10,7 +10,6 @@
 #include <libbutl/path-pattern.mxx>
 
 #include <libbuild2/dump.hxx>
-#include <libbuild2/file.hxx>
 #include <libbuild2/scope.hxx>
 #include <libbuild2/module.hxx>
 #include <libbuild2/target.hxx>
@@ -1435,7 +1434,7 @@ namespace build2
   {
     tracer trace ("parser::parse_include", &path_);
 
-    if (root_->src_path_ == nullptr)
+    if (stage_ == stage::boot)
       fail (t) << "inclusion during bootstrap";
 
     // The rest should be a list of buildfiles. Parse them as names in the
@@ -1933,7 +1932,7 @@ namespace build2
   {
     tracer trace ("parser::parse_import", &path_);
 
-    if (root_->src_path_ == nullptr)
+    if (stage_ == stage::boot)
       fail (t) << "import during bootstrap";
 
     // General import format:
@@ -6090,11 +6089,20 @@ namespace build2
   {
     tracer trace ("parser::switch_scope", &path_);
 
-    auto p (build2::switch_scope (*root_, d));
+    // Switching the project during bootstrap can result in bizarre nesting
+    // with unexpected loading order (e.g., config.build are loaded from inner
+    // to outter rather than the expected reverse). On the other hand, it can
+    // be handy to assign a variable for a nested scope in config.build. So
+    // for this stage we are going to switch the scope without switching the
+    // project expecting the user to know what they are doing.
+    //
+    bool proj (stage_ != stage::boot);
+
+    auto p (build2::switch_scope (*root_, d, proj));
     scope_ = &p.first;
     pbase_ = scope_->src_path_ != nullptr ? scope_->src_path_ : &d;
 
-    if (p.second != root_)
+    if (proj && p.second != root_)
     {
       root_ = p.second;
       l5 ([&]
diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index b21336d..6552114 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -9,6 +9,7 @@
 #include <libbuild2/utility.hxx>
 
 #include <libbuild2/spec.hxx>
+#include <libbuild2/file.hxx>
 #include <libbuild2/lexer.hxx>
 #include <libbuild2/token.hxx>
 #include <libbuild2/variable.hxx>
@@ -21,14 +22,7 @@ namespace build2
   class LIBBUILD2_SYMEXPORT parser
   {
   public:
-    // The project's loading stage during which the parsing is performed.
-    //
-    enum class stage
-    {
-      boot,  // Parsing bootstrap.build (or bootstrap pre/post hooks).
-      root,  // Parsing root.build (or root pre/post hooks).
-      rest   // Parsing the rest (ordinary buildfiles, command line, etc).
-    };
+    using stage = load_stage;
 
     explicit
     parser (context& c, stage s = stage::rest)