add environment evaluation

cibuildwheel/linux.py

@@ -135,7 +135,21 @@ def build(options: BuildOptions) -> None:
 
             if options.before_all:
                 before_all_prepared = prepare_command(options.before_all, project='/project', package=options.package_dir)
-                call(['docker', 'exec', '-i', container_name] + shell_cmd, universal_newlines=True, input=before_all_prepared)
+                task = """
+                PS4='    + '
+
+                set -o errexit
+                set -o xtrace
+
+                {environment_exports}
+
+                {before_all_prepared}
+
+                """.format(
+                    environment_exports='\n'.join(options.environment.as_shell_commands()),
+                    before_all_prepared=before_all_prepared
+                )
+                call(['docker', 'exec', '-i', container_name] + shell_cmd, universal_newlines=True, input=task)
 
             for config in platform_configs:
                 if options.dependency_constraints:

cibuildwheel/macos.py

@@ -177,8 +177,9 @@ def build(options: BuildOptions) -> None:
     repaired_wheel_dir = temp_dir / 'repaired_wheel'
 
     if options.before_all:
+        env = options.environment.as_dictionary(prev_environment=os.environ)
         before_all_prepared = prepare_command(options.before_all, project='.', package=options.package_dir)
-        call([before_all_prepared], shell=True)
+        call([before_all_prepared], shell=True, env=env)
 
     python_configurations = get_python_configurations(options.build_selector)
 

cibuildwheel/windows.py

@@ -163,8 +163,9 @@ def build(options: BuildOptions) -> None:
     download('https://dist.nuget.org/win-x86-commandline/latest/nuget.exe', nuget)
 
     if options.before_all:
+        env = options.environment.as_dictionary(prev_environment=os.environ)
         before_all_prepared = prepare_command(options.before_all, project='.', package=options.package_dir)
-        shell([before_all_prepared])
+        shell([before_all_prepared], env=env)
 
     python_configurations = get_python_configurations(options.build_selector)
     for config in python_configurations: