intro-install_plan: fix destinations for build_targets with custom install_dir

There are a couple issues that combine to make the current handling a
bit confusing.

- we call it "install_dir_name" but it is only ever the class default

- CustomTarget always has it set to None, and then we check if it is
  None then create a different variable with a safe fallback. The if is
  useless -- it cannot fail, but if it did we'd get an undefined
  variable error when we tried to use `dir_name`

Remove the special handling for CustomTarget. Instead, just always
accept None as a possible value of outdir_name when constructing install
data, and, if it is None, fall back to {prefix}/outdir regardless of
what type it used to be.

4 files changed, 26 insertions, 15 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index 0ccb6cd..ff55aad 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -134,7 +134,7 @@ class InstallData:
 class TargetInstallData:
     fname: str
     outdir: str
-    outdir_name: InitVar[str]
+    outdir_name: InitVar[T.Optional[str]]
     strip: bool
     install_name_mappings: T.Mapping[str, str]
     rpath_dirs_to_remove: T.Set[bytes]
@@ -146,7 +146,9 @@ class TargetInstallData:
     tag: T.Optional[str] = None
     can_strip: bool = False
 
-    def __post_init__(self, outdir_name: str) -> None:
+    def __post_init__(self, outdir_name: T.Optional[str]) -> None:
+        if outdir_name is None:
+            outdir_name = os.path.join('{prefix}', self.outdir)
         self.out_name = os.path.join(outdir_name, os.path.basename(self.fname))
 
 @dataclass(eq=False)
@@ -1534,7 +1536,7 @@ class Backend:
         for t in self.build.get_targets().values():
             if not t.should_install():
                 continue
-            outdirs, install_dir_name, custom_install_dir = t.get_install_dir()
+            outdirs, default_install_dir_name, custom_install_dir = t.get_install_dir()
             # Sanity-check the outputs and install_dirs
             num_outdirs, num_out = len(outdirs), len(t.get_outputs())
             if num_outdirs != 1 and num_outdirs != num_out:
@@ -1570,7 +1572,7 @@ class Backend:
                     tag = t.install_tag[0] or ('devel' if isinstance(t, build.StaticLibrary) else 'runtime')
                     mappings = t.get_link_deps_mapping(d.prefix)
                     i = TargetInstallData(self.get_target_filename(t), first_outdir,
-                                          install_dir_name,
+                                          default_install_dir_name,
                                           should_strip, mappings, t.rpath_dirs_to_remove,
                                           t.install_rpath, install_mode, t.subproject,
                                           tag=tag, can_strip=can_strip)
@@ -1595,7 +1597,7 @@ class Backend:
                                 implib_install_dir = self.environment.get_import_lib_dir()
                             # Install the import library; may not exist for shared modules
                             i = TargetInstallData(self.get_target_filename_for_linking(t),
-                                                  implib_install_dir, install_dir_name,
+                                                  implib_install_dir, default_install_dir_name,
                                                   False, {}, set(), '', install_mode,
                                                   t.subproject, optional=isinstance(t, build.SharedModule),
                                                   tag='devel')
@@ -1604,7 +1606,7 @@ class Backend:
                         if not should_strip and t.get_debug_filename():
                             debug_file = os.path.join(self.get_target_dir(t), t.get_debug_filename())
                             i = TargetInstallData(debug_file, first_outdir,
-                                                  install_dir_name,
+                                                  default_install_dir_name,
                                                   False, {}, set(), '',
                                                   install_mode, t.subproject,
                                                   optional=True, tag='devel')
@@ -1616,7 +1618,7 @@ class Backend:
                         if outdir is False:
                             continue
                         f = os.path.join(self.get_target_dir(t), output)
-                        i = TargetInstallData(f, outdir, install_dir_name, False, {}, set(), None,
+                        i = TargetInstallData(f, outdir, default_install_dir_name, False, {}, set(), None,
                                               install_mode, t.subproject,
                                               tag=tag)
                         d.targets.append(i)
@@ -1635,9 +1637,7 @@ class Backend:
                     if first_outdir is not False:
                         for output, tag in zip(t.get_outputs(), t.install_tag):
                             f = os.path.join(self.get_target_dir(t), output)
-                            if not install_dir_name:
-                                dir_name = os.path.join('{prefix}', first_outdir)
-                            i = TargetInstallData(f, first_outdir, dir_name,
+                            i = TargetInstallData(f, first_outdir, default_install_dir_name,
                                                 False, {}, set(), None, install_mode,
                                                 t.subproject, optional=not t.build_by_default,
                                                 tag=tag)
@@ -1648,9 +1648,7 @@ class Backend:
                         if outdir is False:
                             continue
                         f = os.path.join(self.get_target_dir(t), output)
-                        if not install_dir_name:
-                            dir_name = os.path.join('{prefix}', outdir)
-                        i = TargetInstallData(f, outdir, dir_name,
+                        i = TargetInstallData(f, outdir, default_install_dir_name,
                                               False, {}, set(), None, install_mode,
                                               t.subproject, optional=not t.build_by_default,
                                               tag=tag)
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 245f612..3de5ef4 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -624,13 +624,14 @@ class Target(HoldableObject):
 
     def get_install_dir(self) -> T.Tuple[T.List[T.Union[str, Literal[False]]], str, Literal[False]]:
         # Find the installation directory.
-        default_install_dir, install_dir_name = self.get_default_install_dir()
+        default_install_dir, default_install_dir_name = self.get_default_install_dir()
         outdirs = self.get_custom_install_dir()
         if outdirs and outdirs[0] != default_install_dir and outdirs[0] is not True:
             # Either the value is set to a non-default value, or is set to
             # 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
         else:
             custom_install_dir = False
             # if outdirs is empty we need to set to something, otherwise we set
@@ -640,7 +641,7 @@ class Target(HoldableObject):
             else:
                 outdirs = [default_install_dir]
 
-        return outdirs, install_dir_name, custom_install_dir
+        return outdirs, default_install_dir_name, custom_install_dir
 
     def get_basename(self) -> str:
         return self.name
diff --git a/test cases/unit/98 install all targets/meson.build b/test cases/unit/98 install all targets/meson.build
index 3d131e6..c90632a 100644
--- a/test cases/unit/98 install all targets/meson.build
+++ b/test cases/unit/98 install all targets/meson.build
@@ -36,6 +36,10 @@ static_library('static', 'lib.c',
 executable('app', 'main.c',
   install: true,
 )
+executable('app-otherdir', 'main.c',
+  install: true,
+  install_dir: 'otherbin',
+)
 shared_library('shared', 'lib.c',
   install: true,
 )
diff --git a/unittests/allplatformstests.py b/unittests/allplatformstests.py
index 71e919e..6e2f22d 100644
--- a/unittests/allplatformstests.py
+++ b/unittests/allplatformstests.py
@@ -3961,6 +3961,8 @@ class AllPlatformTests(BasePlatformTests):
                 Path(installpath, 'usr/lib/bothcustom.lib'),
                 Path(installpath, 'usr/lib/shared.lib'),
                 Path(installpath, 'usr/lib/versioned_shared.lib'),
+                Path(installpath, 'usr/otherbin'),
+                Path(installpath, 'usr/otherbin/app-otherdir.pdb'),
             }
         elif is_windows() or is_cygwin():
             expected_devel |= {
@@ -3978,6 +3980,8 @@ class AllPlatformTests(BasePlatformTests):
         expected_runtime = expected_common | {
             Path(installpath, 'usr/bin'),
             Path(installpath, 'usr/bin/' + exe_name('app')),
+            Path(installpath, 'usr/otherbin'),
+            Path(installpath, 'usr/otherbin/' + exe_name('app-otherdir')),
             Path(installpath, 'usr/bin/' + exe_name('app2')),
             Path(installpath, 'usr/' + shared_lib_name('shared')),
             Path(installpath, 'usr/' + shared_lib_name('both')),
@@ -4086,6 +4090,10 @@ class AllPlatformTests(BasePlatformTests):
                     'destination': '{bindir}/' + exe_name('app'),
                     'tag': 'runtime',
                 },
+                f'{self.builddir}/' + exe_name('app-otherdir'): {
+                    'destination': '{prefix}/otherbin/' + exe_name('app-otherdir'),
+                    'tag': 'runtime',
+                },
                 f'{self.builddir}/subdir/' + exe_name('app2'): {
                     'destination': '{bindir}/' + exe_name('app2'),
                     'tag': 'runtime',