From 11dce6c2fa7dc39cd9e40c0fedda3280aa2757ad Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 30 Nov 2017 14:50:05 +0200
Subject: Implement module sidebuilds cleanup using scope operation callbacks

---
 build2/cc/compile.cxx | 32 +++++++++++++++-----------------
 build2/cc/init.cxx    | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 build2/cc/utility.cxx |  4 ++++
 build2/cc/utility.hxx |  3 +++
 build2/filesystem.txx |  6 ++++--
 5 files changed, 72 insertions(+), 19 deletions(-)

diff --git a/build2/cc/compile.cxx b/build2/cc/compile.cxx
index 0ab9bfc..ca07b42 100644
--- a/build2/cc/compile.cxx
+++ b/build2/cc/compile.cxx
@@ -3711,6 +3711,9 @@ namespace build2
 
             // Use cc.core.vars as a proxy for {c,cxx}.config (a bit smelly).
             //
+            // This is also the module that registers the scope operation
+            // callback that cleans up the subproject.
+            //
             if (cast_false<bool> ((*s)["cc.core.vars.loaded"]))
               as = s;
 
@@ -3723,11 +3726,7 @@ namespace build2
       // So the first step is to check if the project has already been created
       // and/or loaded and if not, then to go ahead and do so.
       //
-      dir_path pd (as->out_path ());
-      pd /= "build";
-      pd /= "cc";
-      pd /= "modules";
-      pd /= x;
+      dir_path pd (as->out_path () / modules_sidebuild_dir /= x);
       {
         const scope* ps (&scopes.find (pd));
 
@@ -3758,18 +3757,17 @@ namespace build2
 
               extra += string (x) + ".features.modules = true";
 
-              dir_path ad (((dir_path ("..") /= "..") /= "..") /= "..");
-
-              config::create_project (pd,
-                                      ad,                 /* amalgamation */
-                                      {},                 /* boot_modules */
-                                      extra,              /* root_pre */
-                                      {string (x) + '.'}, /* root_modules */
-                                      "",                 /* root_post */
-                                      false,              /* config */
-                                      false,              /* buildfile */
-                                      "the cc module",
-                                      2);                 /* verbosity */
+              config::create_project (
+                pd,
+                as->out_path ().relative (pd),  /* amalgamation */
+                {},                             /* boot_modules */
+                extra,                          /* root_pre */
+                {string (x) + '.'},             /* root_modules */
+                "",                             /* root_post */
+                false,                          /* config */
+                false,                          /* buildfile */
+                "the cc module",
+                2);                             /* verbosity */
             }
 
             ps = &load_project (as->rw () /* lock */, pd, pd);
diff --git a/build2/cc/init.cxx b/build2/cc/init.cxx
index 87a7b12..3108d6d 100644
--- a/build2/cc/init.cxx
+++ b/build2/cc/init.cxx
@@ -4,13 +4,16 @@
 
 #include <build2/cc/init.hxx>
 
+#include <build2/file.hxx>
 #include <build2/scope.hxx>
 #include <build2/context.hxx>
+#include <build2/filesystem.hxx>
 #include <build2/diagnostics.hxx>
 
 #include <build2/config/utility.hxx>
 
 #include <build2/cc/target.hxx>
+#include <build2/cc/utility.hxx>
 
 using namespace std;
 using namespace butl;
@@ -19,6 +22,39 @@ namespace build2
 {
   namespace cc
   {
+    // Scope operation callback that cleans up module sidebuilds.
+    //
+    static target_state
+    clean_module_sidebuilds (action, const scope& rs, const dir&)
+    {
+      dir_path d (rs.out_path () / modules_sidebuild_dir);
+
+      if (exists (d))
+      {
+        if (build2::rmdir_r (d))
+        {
+          // Clean up cc/ if it became empty.
+          //
+          d = rs.out_path () / module_dir;
+          if (empty (d))
+          {
+            rmdir (d);
+
+            // And build/ if it also became empty (e.g., in case of a build
+            // with a transient configuration).
+            //
+            d = rs.out_path () / build_dir;
+            if (empty (d))
+              rmdir (d);
+          }
+
+          return target_state::changed;
+        }
+      }
+
+      return target_state::unchanged;
+    }
+
     bool
     core_vars_init (scope& rs,
                     scope&,
@@ -88,6 +124,16 @@ namespace build2
       v.insert<bool> ("config.cc.reprocess", true);
       v.insert<bool> ("cc.reprocess");
 
+      // Register scope operation callback.
+      //
+      // It feels natural to do clean up sidebuilds as a post operation but
+      // that prevents the (otherwise-empty) out root directory to be cleaned
+      // up (via the standard fsdir{} chain).
+      //
+      rs.operation_callbacks.emplace (
+        perform_clean_id,
+        scope::operation_callback {&clean_module_sidebuilds, nullptr /*post*/});
+
       return true;
     }
 
diff --git a/build2/cc/utility.cxx b/build2/cc/utility.cxx
index 7a2b7fe..aa47085 100644
--- a/build2/cc/utility.cxx
+++ b/build2/cc/utility.cxx
@@ -4,6 +4,7 @@
 
 #include <build2/cc/utility.hxx>
 
+#include <build2/file.hxx>
 #include <build2/variable.hxx>
 #include <build2/algorithm.hxx> // search()
 
@@ -17,6 +18,9 @@ namespace build2
   {
     using namespace bin;
 
+    const dir_path module_dir (dir_path ("build") /= "cc");
+    const dir_path modules_sidebuild_dir (dir_path (module_dir) /= "modules");
+
     lorder
     link_order (const scope& bs, otype ot)
     {
diff --git a/build2/cc/utility.hxx b/build2/cc/utility.hxx
index 2f6834f..d7d980d 100644
--- a/build2/cc/utility.hxx
+++ b/build2/cc/utility.hxx
@@ -19,6 +19,9 @@ namespace build2
 
   namespace cc
   {
+    extern const dir_path module_dir;             // build/cc/
+    extern const dir_path modules_sidebuild_dir;  // build/cc/modules/
+
     // Compile output type.
     //
     otype
diff --git a/build2/filesystem.txx b/build2/filesystem.txx
index fe56498..8e50592 100644
--- a/build2/filesystem.txx
+++ b/build2/filesystem.txx
@@ -2,6 +2,8 @@
 // copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <type_traits> // is_base_of
+
 #include <build2/context.hxx>     // work
 #include <build2/diagnostics.hxx>
 
@@ -64,9 +66,9 @@ namespace build2
       if (verb >= v)
       {
         if (verb >= 2)
-          text << "rm " << d;
+          text << "rmdir " << d;
         else if (verb)
-          text << "rm " << t;
+          text << (std::is_base_of<dir_path, T>::value ? "rmdir " : "rm ") << t;
       }
     };
 
-- 
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