Actualize project root directories

This solves the problem of changing path spelling on platforms with case-
insensitive filesystems.

For example, you may build a project in the current working directory without
specifying any paths. This means the current working directory will be used as
the project's root. On Windows this could be C:\x.

Now you are building another project that imports the above project and you
specify config.import.x variable pointing to the above build. But you are lazy
to type capital C so you spell it as config.import.x=c:\x.

What happens now is the value from config.import.x is used as the project
root. And now it is a different spelling compared to your original build. This
is not a problem when the build system itself is concerned -- it is smart
enough to use case-insensitive comparison. However, we often use roots to
derive other things, say, -I options that we pass to compilers. And these
options are normally no longer treated as (case-insensitive) paths. If they
are hashed and the result stored in depdb, then we end up with rebuilds that
are triggered by changes from C:\ to c:\.

1 files changed, 9 insertions, 7 deletions

diff --git a/build2/file b/build2/file
index 00ece85..062487a 100644
--- a/build2/file
+++ b/build2/file
@@ -34,17 +34,19 @@ namespace build2
   bool
   is_out_root (const dir_path&);
 
-  // Given an src_base directory, look for a project's src_root
-  // based on the presence of known special files. Return empty
-  // path if not found.
+  // Given an src_base directory, look for a project's src_root based on the
+  // presence of known special files. Return empty path if not found. Note
+  // that if the input is normalized/actualized, then the output will be as
+  // well.
   //
   dir_path
   find_src_root (const dir_path&);
 
-  // The same as above but for project's out. Note that we also
-  // check whether a directory happens to be src_root, in case
-  // this is an in-tree build. The second argument is the out
-  // flag that is set to true if this is src_root.
+  // The same as above but for project's out. Note that we also check whether
+  // a directory happens to be src_root, in case this is an in-tree build. The
+  // second argument is the out flag that is set to true if this is src_root.
+  // Note that if the input is normalized/actualized, then the output will be
+  // as well.
   //
   dir_path
   find_out_root (const dir_path&, bool* src = nullptr);