Set up environment during build preparations (alire-project#1766)

* Set up environment during build preparations

* Test

src/alire/alire-roots.adb

@@ -98,6 +98,10 @@ package body Alire.Roots is
       --  Will regenerate on demand only those changed. For shared
       --  dependencies, will also generate any missing configs not generated
       --  during sync, such as for linked releases and the root release.
+
+      --  Set the environment to be used during build
+
+      This.Export_Build_Environment;
    end Build_Prepare;
 
    -----------
@@ -276,8 +280,6 @@ package body Alire.Roots is
          return True;
       end if;
 
-      This.Export_Build_Environment;
-
       This.Traverse (Build_Single_Release'Access);
 
       return True;

testsuite/tests/action/environment/test.py

@@ -0,0 +1,51 @@
+"""
+Verify the proper environment is set up for the action. We create an executable
+within a crate that will be run during pre-build. For it to be found, the
+proper path must be set in the crate environment. This should work for a
+regular build (as it did before) and for a manually triggered action (the bug
+being fixed).
+"""
+
+import os
+from shutil import which
+from drivers.alr import run_alr, init_local_crate, add_action, alr_manifest
+from drivers.asserts import assert_eq
+from drivers.helpers import content_of, on_windows
+
+tool_name = "myalrtestingtool"
+
+# Tool crate to be used during build
+init_local_crate(tool_name, enter=False)
+
+# Ensure the tool is not found in path by pure chance!
+assert not which(tool_name)
+
+# Build the tool
+run_alr("-C", tool_name, "build")
+
+# Create the new crate that uses this tool during pre-build step
+init_local_crate()
+
+# Edit its manifest to require it during pre-build
+add_action("pre-build", [tool_name + (".exe" if on_windows() else "")])
+
+# Build should fail because the tool is not found in the path
+run_alr("build", complain_on_error=False)
+
+# Likewise, stand-alone running of the action should fail
+run_alr("action", "pre-build", complain_on_error=False)
+
+# Add the tool location to the crate environment
+with open(alr_manifest(), "at") as f:
+    f.write(f"""
+[environment]
+PATH.prepend = "../{tool_name}/bin"
+""")
+
+# assert_eq(content_of(alr_manifest()), "XXX")
+
+# Now both build and action should succeed
+run_alr("build")
+run_alr("action", "pre-build")
+
+print("SUCCESS")

testsuite/tests/action/environment/test.yaml

@@ -0,0 +1,4 @@
+driver: python-script
+build_mode: both
+indexes:
+    compiler_only_index: {}