From 60e054bbac499cf9258df04ca0f8cc25e6981839 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 6 Sep 2023 12:47:59 +0200
Subject: Make GCC plugin directory, g++ executable name customizable

Specifically, there are now two new optional configuration variables:

config [dir_path] config.odb.plugin_dir ?= [null]
config [string] config.odb.gxx_name ?= [null]
---
 build/root.build | 60 ++++++++++++++++++++++++++++++++++++++++++++++----------
 odb/buildfile    | 21 ++++----------------
 2 files changed, 54 insertions(+), 27 deletions(-)

diff --git a/build/root.build b/build/root.build
index a07e058..4a28331 100644
--- a/build/root.build
+++ b/build/root.build
@@ -1,6 +1,20 @@
 # file      : build/root.build
 # license   : GNU GPL v3; see accompanying LICENSE file
 
+# This configuration variable can be used to specify the GCC plugin directory
+# instead of auto-discovering it with -print-file-name=plugin. Primarily
+# useful when dealing with cross-compilation.
+#
+config [dir_path, config.report.variable=plugin_dir] \
+  config.odb.plugin_dir ?= [null]
+
+# This configuration variable can be used to specify the GCC g++ executable
+# name that will be called by the ODB compiler instead of auto-deriving it
+# from config.cxx. Primarily useful when dealing with cross-compilation.
+#
+config [string, config.report.variable=gxx_name] \
+  config.odb.gxx_name ?= [null]
+
 config [bool] config.odb.develop ?= false
 
 develop = $config.odb.develop
@@ -36,22 +50,48 @@ if ($build.mode != 'skeleton')
   if ($cxx.id != 'gcc')
     fail 'ODB compiler can only be built with GCC'
 
-  # Determine the GCC plugin directory.
-  #
-  # If plugin support is disabled, then -print-file-name will print the name
-  # we have passed (the real plugin directory will always be absolute).
+  # Determine the GCC plugin directory unless specified explicitly.
   #
+  if ($config.odb.plugin_dir != [null])
+    plugin_dir = $config.odb.plugin_dir
+  else
+  {
+    # If plugin support is disabled, then -print-file-name will print the name
+    # we have passed (the real plugin directory will always be absolute).
+    #
+    plugin_dir = [dir_path] $process.run($cxx.path -print-file-name=plugin)
+
+    if ("$plugin_dir" == plugin)
+      fail "$recall($cxx.path) does not support plugins"
+  }
+
   # It can also include '..' components (e.g., on Windows) so normalize it for
   # good measure.
   #
-  plugin_dir = [dir_path] $process.run($cxx.path -print-file-name=plugin)
-
-  if ("$plugin_dir" == plugin)
-    fail "$recall($cxx.path) does not support plugins"
-
   plugin_dir = $normalize($plugin_dir)
 
-  config [config.report] plugin_dir
+  # Determine the g++ executable name unless specified explicitly.
+  #
+  if ($config.odb.gxx_name != [null])
+    gxx_name = $config.odb.gxx_name
+  else
+  {
+    # Unless cross-compiling, pass the C++ compiler's recall path as the g++
+    # name.
+    #
+    # Note that we used to compare complete target triplets but that prooved
+    # too strict. For example, we may be running on x86_64-apple-darwin17.7.0
+    # while the compiler is targeting x86_64-apple-darwin17.3.0.
+    #
+    if ($cxx.target.cpu    == $build.host.cpu && \
+        $cxx.target.system == $build.host.system)
+    {
+      gxx_name = $recall($cxx.path)
+    }
+    else
+      fail "g++ executable name must be specified explicitly with \
+config.odb.gxx_name when cross-compiling"
+  }
 
   # Extract the copyright notice from the LICENSE file.
   #
diff --git a/odb/buildfile b/odb/buildfile
index 20f8718..34a6329 100644
--- a/odb/buildfile
+++ b/odb/buildfile
@@ -32,22 +32,6 @@ if ($cxx.target.class != 'windows')
 #
 plugin{*}: install = bin/
 
-# Unless cross-compiling, pass the C++ compiler's recall path as the g++
-# name. At some point we should also make it configurable.
-#
-# Note that we used to compare complete target triplets but that prooved too
-# strict. For example, we may be running on x86_64-apple-darwin17.7.0 while
-# the compiler is targeting x86_64-apple-darwin17.3.0.
-#
-if ($cxx.target.cpu    == $build.host.cpu && \
-    $cxx.target.system == $build.host.system)
-{
-  gxx_name = $recall($cxx.path)
-  gxx_name = $regex.replace($gxx_name, '\\', '\\\\') # Escape back slashes.
-}
-else
-  gxx_name = g++
-
 import libs  = libcutl%lib{cutl}
 import libs += libstudxml%lib{studxml}
 
@@ -98,7 +82,10 @@ libus{odb}: {hxx ixx txx cxx}{** -odb -options -pregenerated/**} $libs
 
 # Build options.
 #
-cxx.poptions += "-I$plugin_dir/include" "-DODB_GXX_NAME=\"$gxx_name\""
+# Note: escape backslashes in gxx_name.
+#
+cxx.poptions += "-I$plugin_dir/include"
+cxx.poptions += "-DODB_GXX_NAME=\"$regex.replace($gxx_name, '\\', '\\\\')\""
 cxx.poptions += -DODB_BUILD2 # @@ TMP while supporting other build systems.
 
 ## Consumption build ($develop == false).
-- 
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