introspection: untangle install_plan implemetation, fix a bunch of wrong ones

Generally plumb through the values of get_option() passed to
install_dir, and use this to establish the install plan name. Fixes
several odd cases, such as:

- {datadir} being prepended to "share" or "include"

- dissociating custom install directories and writing them out as
  {prefix}/share/foo or {prefix}/lib/python3.10/site-packages

This is the second half of #9478
Fixes #10601

1 files changed, 3 insertions, 2 deletions

diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 2729373..c7f5997 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -628,7 +628,7 @@ class Target(HoldableObject):
             # False (which means we want this specific output out of many
             # outputs to not be installed).
             custom_install_dir = True
-            default_install_dir_name = None
+            install_dir_names = [getattr(i, 'optname', None) for i in outdirs]
         else:
             custom_install_dir = False
             # if outdirs is empty we need to set to something, otherwise we set
@@ -637,8 +637,9 @@ class Target(HoldableObject):
                 outdirs[0] = default_install_dir
             else:
                 outdirs = [default_install_dir]
+            install_dir_names = [default_install_dir_name] * len(outdirs)
 
-        return outdirs, default_install_dir_name, custom_install_dir
+        return outdirs, install_dir_names, custom_install_dir
 
     def get_basename(self) -> str:
         return self.name