move CMAKE_PREFIX_PATH env var handling to environment

This causes the variable to be read up front and stored, rather than be
re-read on each invocation of meson.

This does have two slight behavioral changes. First is the obvious one
that changing the variable between `meson --reconfigure` invocations has
no effect. This is the way PKG_CONFIG_PATH already works. The second
change is that CMAKE_PREFIX_PATH the env var is no longer appended to
the values set in the machine file or on the command line, and is
instead replaced by them. CMAKE_PREFIX_PATH is the only env var in meson
that works this way, every other one is replaced not appended, so while
this is a behavioral change, I also think its a bug fix.

2 files changed, 20 insertions, 24 deletions

diff --git a/mesonbuild/cmake/executor.py b/mesonbuild/cmake/executor.py
index 674b854..e4b85de 100644
--- a/mesonbuild/cmake/executor.py
+++ b/mesonbuild/cmake/executor.py
@@ -24,7 +24,6 @@ import os
 
 from .. import mlog
 from ..mesonlib import PerMachine, Popen_safe, version_compare, MachineChoice, is_windows, OptionKey
-from ..envconfig import get_env_var
 
 if T.TYPE_CHECKING:
     from ..environment import Environment
@@ -63,23 +62,6 @@ class CMakeExecutor:
             return
 
         self.prefix_paths = self.environment.coredata.options[OptionKey('cmake_prefix_path', machine=self.for_machine)].value
-        env_pref_path_raw = get_env_var(
-            self.for_machine,
-            self.environment.is_cross_build(),
-            'CMAKE_PREFIX_PATH')
-        if env_pref_path_raw is not None:
-            env_pref_path = []  # type: T.List[str]
-            if is_windows():
-                # Cannot split on ':' on Windows because its in the drive letter
-                env_pref_path = env_pref_path_raw.split(os.pathsep)
-            else:
-                # https://github.com/mesonbuild/meson/issues/7294
-                env_pref_path = re.split(r':|;', env_pref_path_raw)
-            env_pref_path = [x for x in env_pref_path if x]  # Filter out empty strings
-            if not self.prefix_paths:
-                self.prefix_paths = []
-            self.prefix_paths += env_pref_path
-
         if self.prefix_paths:
             self.extra_cmake_args += ['-DCMAKE_PREFIX_PATH={}'.format(';'.join(self.prefix_paths))]
 
diff --git a/mesonbuild/environment.py b/mesonbuild/environment.py
index 59675ff..7555be5 100644
--- a/mesonbuild/environment.py
+++ b/mesonbuild/environment.py
@@ -1,4 +1,4 @@
-# Copyright 2012-2016 The Meson development team
+# Copyright 2012-2020 The Meson development team
 
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -579,7 +579,7 @@ class Environment:
         # Stores machine infos, the only *three* machine one because we have a
         # target machine info on for the user (Meson never cares about the
         # target machine.)
-        machines = PerThreeMachineDefaultable()  # type: PerMachineDefaultable[MachineInfo]
+        machines: PerThreeMachineDefaultable[MachineInfo] = PerThreeMachineDefaultable()
 
         # Similar to coredata.compilers, but lower level in that there is no
         # meta data, only names/paths.
@@ -751,14 +751,28 @@ class Environment:
 
     def set_default_options_from_env(self) -> None:
         for for_machine in MachineChoice:
-            for evar, keyname in [('PKG_CONFIG_PATH', 'pkg_config_path')]:
+            for evar, keyname in [('PKG_CONFIG_PATH', 'pkg_config_path'),
+                                  ('CMAKE_PREFIX_PATH', 'cmake_prefix_path')]:
                 p_env_pair = get_env_var_pair(for_machine, self.is_cross_build(), evar)
                 if p_env_pair is not None:
                     _, p_env = p_env_pair
 
-                    # PKG_CONFIG_PATH may contain duplicates, which must be
-                    # removed, else a duplicates-in-array-option warning arises.
-                    p_list = list(mesonlib.OrderedSet(p_env.split(':')))
+                    # these may contain duplicates, which must be removed, else
+                    # a duplicates-in-array-option warning arises.
+                    if keyname == 'cmake_prefix_path':
+                        if self.machines[for_machine].is_windows():
+                            # Cannot split on ':' on Windows because its in the drive letter
+                            _p_env = p_env.split(os.pathsep)
+                        else:
+                            # https://github.com/mesonbuild/meson/issues/7294
+                            _p_env = re.split(r':|;', p_env)
+                        p_list = list(mesonlib.OrderedSet(_p_env))
+                    elif keyname == 'pkg_config_path':
+                        p_list = list(mesonlib.OrderedSet(p_env.split(':')))
+                    else:
+                        raise RuntimeError('Should be unreachable')
+                    p_list = [e for e in p_list if e]  # filter out any empty eelemnts
+
                     # Take env vars only on first invocation, if the env changes when
                     # reconfiguring it gets ignored.
                     # FIXME: We should remember if we took the value from env to warn