commit 93b63e8f3b4880927ccbd5522c967df79e926cda
author Sutou Kouhei <kou@clear-code.com> Tue Aug 30 13:57:58 2022 +0900
committer GitHub <noreply@github.com> Tue Aug 30 13:57:58 2022 +0900
tree e231152118547657093fad2eb4d56eeec90ababf
parent b43c6f6b18acee019a500bc6a05af18c07f2ca79

ARROW-12175: [C++] Fix CMake packages (#13892)

ARROW-9171 and ARROW-17231 are also fixed.

Our CMake packages are broken. For example, `find_package(Parquet)`
doesn't work without specifying `CMAKE_MODULE_PATH`.

`find_package(${PACKAGE})` searches
`${PREFIX}/${PACKAGE}/${PACKAGE}Config.cmake` or
`${PREFIX}/${PACKAGE}/Find${PACKAGE}.cmake`. But our .cmake files are
always installed `${PREFIX}/arrow/`. So `find_package(Parquet)` can't find
`${PREFIX}/arrow/FindParquet.cmake` because "`/arrow/`" isn't
"`/${PACKAGE}`".

This change fixes this by installing `${PACKAGE}Config.cmake` to
`${PREFIX}/${PACKAGE}/` instead of `${PREFIX}/arrow/`.

This also removes all `Find${PACKAGE}.cmake`. We only provides
`${PACKAGE}Config.cmake`. Our `Find${PACKAGE}.cmake` can find `${PACKAGE}`
by CMake, pkg-config or manual .so/.h search. But we don't need to
support pkg-config nor manual .so/.h search. We can use
`${PACKAGE}Config.cmake` to support CMake package search. So this
removes all `Find${PACKAGE}.cmake`.

This also introduces namespace to our CMake targets. For example,
`arrow_shared` is exported as `Arrow::arrow_shared` and
`parquet_static` is exported as `Parquet::parquet_static`. But no
namespace targets such as `arrow_shared` and `parquet_static` are
still also exported for keeping backward compatibility. But this
requires CMake 3.18 or later for users because `add_library(ALIAS)`
for non-global `IMPORTED` library is available since CMake 3.18.

(`Plasma::plasma-store-server` target is also added for
`plasma-store-server` executable.)

FYI: We can resolve this problem by using `COMPONENTS` feature of
`find_package()`. For example, `find_package(Arrow COMPONENTS
Parquet)` is used instead of `find_package(Parquet)`. With
`COMPONENTS`, `${PACKAGE}` is always "Arrow". So we can still install
our .cmake files to `${PREFIX}/arrow/`. But this approach breaks
backward compatibility. So I choose `${PREFIX}/${PACKAGE}/*.cmake`
approach.


Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>