Add boost_root support to properties files (#7210)

* Add boost_root support to properties files

This commit implements `boost_root`, `boost_includedir`, and
`boost_librarydir` variable support to native and cross properties
files. The search order is currently environment variables, then
these variables, and finally a platform-dependent search.

* Add preliminary boost_root / boost_includedir tests

Each test contains a fake "version.hpp", as that's how boost detection is
currently being done. We look for this file relative to the root directory,
which probably shouldn't be allowed (it previously was for BOOST_LIBRARYDIR
but not for BOOST_ROOT). It also cannot help with breakage detection in
libraries, however it looks like this wasn't getting tested beforehand.

I've given the two unique version numbers that shouldn't be present in any
stock version of boost (001 and 002).

* Add return type to detect_split_root

* Return empty list when nothing found in BOOST_ROOT, rather than None

* Update boost_root tests

* Create nativefile.ini based on location of run_project_tests.py
* Add fake libraries to ensure boost_librarydir is being used

* Require all search paths for boost to be absolute

* Redo boost search ordering

To better match things like pkg-config, we now look through native/cross files,
then environment variables, then system locations for boost installations.

Path detection does not fall back from one method to the next for properties or
environment variables--if boost_root, boost_librarydir, or boost_includedir is
specified, they must be sufficient to find boost. Likewise for BOOST_ROOT and
friends. pkg-config detection is still optional falling back to system-wide
detection, for Conan.

(Also, fix a typo in test 33's nativefile)

* Correct return type for detect_roots

* Correct boost dependency search order in documentation

* Print debug information for boost library finding, to resolve CI issues

* Handle native/cross file templates in a more consistent way

All tests can now create a `nativefile.ini.in` if they need to use some
parameter that the testing framework knows about but they can't.

* Pass str--rather than PosixPath--to os.path.exists, for Python35

* Look for boost minor versions, rather than boost patch versions in test cases

* Drop fake dylib versions of boost_regex

* Prefer get_env_var to use of os.environ

* Correct error reporting for relative BOOST_ROOT paths

* Bump version this appears in. Also, change "properties file" to "machine file" as that appears to be the more common language.

1 files changed, 6 insertions, 2 deletions

diff --git a/docs/markdown/Dependencies.md b/docs/markdown/Dependencies.md
index a8f6d8a..b89a0aa 100644
--- a/docs/markdown/Dependencies.md
+++ b/docs/markdown/Dependencies.md
@@ -288,8 +288,12 @@ You can call `dependency` multiple times with different modules and
 use those to link against your targets.
 
 If your boost headers or libraries are in non-standard locations you
-can set the BOOST_ROOT, BOOST_INCLUDEDIR, and/or BOOST_LIBRARYDIR
-environment variables.
+can set the `BOOST_ROOT`, or the `BOOST_INCLUDEDIR` and `BOOST_LIBRARYDIR`
+environment variables. *(added in 0.56.0)* You can also set these
+parameters as `boost_root`, `boost_include`, and `boost_librarydir` in your
+native or cross machine file. Note that machine file variables are
+preferred to environment variables, and that specifying any of these
+disables system-wide search for boost.
 
 You can set the argument `threading` to `single` to use boost
 libraries that have been compiled for single-threaded use instead.