From f62b8809d827a0474284e75ad5724cf201ed83b1 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 22 Mar 2023 10:45:51 +0200
Subject: Initial work on relocatable install: config.install.relocatable and
 rpath

---
 libbuild2/bin/init.cxx     |  3 ++
 libbuild2/cc/link-rule.cxx | 68 ++++++++++++++++++++++++++++++++++++++++++++--
 libbuild2/install/init.cxx | 25 +++++++++++++++--
 3 files changed, 92 insertions(+), 4 deletions(-)

diff --git a/libbuild2/bin/init.cxx b/libbuild2/bin/init.cxx
index c5b58bb..1bdf6a6 100644
--- a/libbuild2/bin/init.cxx
+++ b/libbuild2/bin/init.cxx
@@ -79,6 +79,9 @@ namespace build2
       // example, addition of rpaths for prerequisite libraries (see the cc
       // module for an example). Default is true.
       //
+      // Note also that a rule may need to make rpath relative if
+      // install.relocatable is true.
+      //
       vp.insert<dir_paths> ("config.bin.rpath");
       vp.insert<bool>      ("config.bin.rpath.auto");
 
diff --git a/libbuild2/cc/link-rule.cxx b/libbuild2/cc/link-rule.cxx
index 99aa421..f860fdc 100644
--- a/libbuild2/cc/link-rule.cxx
+++ b/libbuild2/cc/link-rule.cxx
@@ -20,6 +20,8 @@
 #include <libbuild2/bin/target.hxx>
 #include <libbuild2/bin/utility.hxx>
 
+#include <libbuild2/install/utility.hxx>
+
 #include <libbuild2/cc/target.hxx>  // c, pc*
 #include <libbuild2/cc/utility.hxx>
 
@@ -3264,10 +3266,72 @@ namespace build2
             rpath_libraries (sargs, bs, a, t, li, for_install /* link */);
 
           lookup l;
-
           if ((l = t["bin.rpath"]) && !l->empty ())
+          {
+            // See if we need to make the specified paths relative using the
+            // $ORIGIN (Linux, BSD) or @loader_path (Mac OS) mechanisms.
+            //
+            optional<dir_path> origin;
+            if (for_install && cast_false<bool> (rs["install.relocatable"]))
+            {
+              // Note that both $ORIGIN and @loader_path will be expanded to
+              // the path of the binary that we are building (executable or
+              // shared library) as opposed to top-level executable.
+              //
+              path p (install::resolve_file (t));
+
+              // If the file is not installable then the install.relocatable
+              // semantics does not apply, naturally.
+              //
+              if (!p.empty ())
+                origin = p.directory ();
+            }
+
+            bool origin_used (false);
             for (const dir_path& p: cast<dir_paths> (l))
-              sargs.push_back ("-Wl,-rpath," + p.string ());
+            {
+              string o ("-Wl,-rpath,");
+
+              // Note that we only rewrite absolute paths so if the user
+              // specified $ORIGIN or @loader_path manually, we will pass it
+              // through as is.
+              //
+              if (origin && p.absolute ())
+              {
+                dir_path l;
+                try
+                {
+                  l = p.relative (*origin);
+                }
+                catch (const invalid_path&)
+                {
+                  fail << "unable to make rpath " << p << " relative to "
+                       << *origin <<
+                    info << "required for relocatable installation";
+                }
+
+                o += (tclass == "macos" ? "@loader_path" : "$ORIGIN");
+
+                if (!l.empty ())
+                {
+                  o += path_traits::directory_separator;
+                  o += l.string ();
+                }
+
+                origin_used = true;
+              }
+              else
+                o += p.string ();
+
+              sargs.push_back (move (o));
+            }
+
+            // According to the Internet, `-Wl,-z,origin` is not needed except
+            // potentially for older BSDs.
+            //
+            if (origin_used && tclass == "bsd")
+              sargs.push_back ("-Wl,-z,origin");
+          }
 
           if ((l = t["bin.rpath_link"]) && !l->empty ())
           {
diff --git a/libbuild2/install/init.cxx b/libbuild2/install/init.cxx
index 92c2790..a3155d1 100644
--- a/libbuild2/install/init.cxx
+++ b/libbuild2/install/init.cxx
@@ -421,9 +421,9 @@ namespace build2
         using config::lookup_config;
         using config::specified_config;
 
-        // Note: ignore config.install.scope (see below).
+        // Note: ignore config.install.{scope,manifest} (see below).
         //
-        bool s (specified_config (rs, "install", {"scope"}));
+        bool s (specified_config (rs, "install", {"scope", "manifest"}));
 
         // Adjust module priority so that the (numerous) config.install.*
         // values are saved at the end of config.build.
@@ -582,6 +582,27 @@ namespace build2
           }
         }
 
+        // Support for relocatable install.
+        //
+        // Note that it is false by default since supporting relocatable
+        // installation may require extra effort and not all projects may
+        // support it. A project that is known not to support it should assert
+        // this fact in its root.build, for example:
+        //
+        // assert (!$install.relocatable) 'relocatable installation not supported'
+        //
+        {
+          auto& var  (vp.insert<bool> (       "install.relocatable"));
+          auto& cvar (vp.insert<bool> ("config.install.relocatable"));
+
+          value& v (rs.assign (var));
+
+          // Note: unlike other variables, for ease of assertion set it to
+          // false if no config.install.* is specified.
+          //
+          v = s && cast_false<bool> (lookup_config (rs, cvar, false));
+        }
+
         // Global config.install.* values.
         //
         set_dir (s, p, rs, "",             abs_dir_path (), false, "644", "755", cmd);
-- 
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