add logging to help users debug where external file searches are taking a long time (#35900)

lib/spack/spack/build_environment.py

@@ -485,7 +485,13 @@ def update_compiler_args_for_dep(dep):
             query = pkg.spec[dep.name]
             dep_link_dirs = list()
             try:
+                # In some circumstances (particularly for externals) finding
+                # libraries packages can be time consuming, so indicate that
+                # we are performing this operation (and also report when it
+                # finishes).
+                tty.debug("Collecting libraries for {0}".format(dep.name))
                 dep_link_dirs.extend(query.libs.directories)
+                tty.debug("Libraries for {0} have been collected.".format(dep.name))
             except NoLibrariesError:
                 tty.debug("No libraries found for {0}".format(dep.name))
 
@@ -772,7 +778,9 @@ def setup_package(pkg, dirty, context="build"):
         set_compiler_environment_variables(pkg, env_mods)
         set_wrapper_variables(pkg, env_mods)
 
+    tty.debug("setup_package: grabbing modifications from dependencies")
     env_mods.extend(modifications_from_dependencies(pkg.spec, context, custom_mods_only=False))
+    tty.debug("setup_package: collected all modifications from dependencies")
 
     # architecture specific setup
     platform = spack.platforms.by_name(pkg.spec.architecture.platform)
@@ -780,6 +788,7 @@ def setup_package(pkg, dirty, context="build"):
     platform.setup_platform_environment(pkg, env_mods)
 
     if context == "build":
+        tty.debug("setup_package: setup build environment for root")
         builder = spack.builder.create(pkg)
         builder.setup_build_environment(env_mods)
 
@@ -790,6 +799,7 @@ def setup_package(pkg, dirty, context="build"):
                 " includes and omit it when invoked with '--cflags'."
             )
     elif context == "test":
+        tty.debug("setup_package: setup test environment for root")
         env_mods.extend(
             inspect_path(
                 pkg.spec.prefix,
@@ -806,6 +816,7 @@ def setup_package(pkg, dirty, context="build"):
     # Load modules on an already clean environment, just before applying Spack's
     # own environment modifications. This ensures Spack controls CC/CXX/... variables.
     if need_compiler:
+        tty.debug("setup_package: loading compiler modules")
         for mod in pkg.compiler.modules:
             load_module(mod)
 
@@ -943,6 +954,7 @@ def default_modifications_for_dep(dep):
             _make_runnable(dep, env)
 
     def add_modifications_for_dep(dep):
+        tty.debug("Adding env modifications for {0}".format(dep.name))
         # Some callers of this function only want the custom modifications.
         # For callers that want both custom and default modifications, we want
         # to perform the default modifications here (this groups custom
@@ -968,6 +980,7 @@ def add_modifications_for_dep(dep):
                 builder.setup_dependent_build_environment(env, spec)
             else:
                 dpkg.setup_dependent_run_environment(env, spec)
+        tty.debug("Added env modifications for {0}".format(dep.name))
 
     # Note that we want to perform environment modifications in a fixed order.
     # The Spec.traverse method provides this: i.e. in addition to