refactor!: revert {task_workdir} interpolation in run-task environment

In hindsight, this ended up being a bad idea and caused lots of subtle
issues in Gecko. As an alternative, I landed a change to get
generic-worker itself to set $TASK_WORKDIR.

This will take awhile to propagate to all pools, but in the meantime
it's cleanest to revert back to the abspath method.

docs/reference/migrations.rst

@@ -3,6 +3,14 @@ Migration Guide
 
 This page can help when migrating Taskgraph across major versions.
 
+13.x -> 14.x
+------------
+
+* The `{task_workdir}` string in environment variables no longer gets
+  interpolated by `run-task`. This is backing out a feature introduced in
+  version 13.x, so this release introduces no new backwards incompatibilities
+  with version 12.x or earlier.
+
 12.x -> 13.x
 ------------
 

src/taskgraph/run-task/run-task

@@ -1257,24 +1257,20 @@ def main(args):
     for repo in repositories:
         vcs_checkout_from_args(repo)
 
-    # Interpolate environment variables with defined substitution patterns. For
-    # example, the variable `CACHE_DIR={task_workdir}/.cache` will be
-    # interpolated with the task's working directory.
-    env_subs = {
-        "task_workdir": task_workdir,
-    }
-    for k, v in os.environ.items():
-        for subname, subval in env_subs.items():
-            # We check for an exact match rather than using a format string to
-            # avoid accidentally trying to interpolate environment variables
-            # that happen to contain brackets for some other reason.
-            pattern = f"{{{subname}}}"
-            if pattern in v:
-                os.environ[k] = v.replace(pattern, subval)
-                print_line(
-                    b"setup",
-                    b"%s is %s\n" % (k.encode("utf-8"), os.environ[k].encode("utf-8")),
-                )
+    # Convert certain well known environment variables to absolute paths.
+    for k in [
+        "CARGO_HOME",
+        "MOZ_FETCHES_DIR",
+        "PIP_CACHE_DIR",
+        "UPLOAD_DIR",
+        "UV_CACHE_DIR",
+        "npm_config_cache",
+    ] + [
+        "{}_PATH".format(repository["project"].upper())
+        for repository in repositories
+    ]:
+        if k in os.environ:
+            os.environ[k] = os.path.abspath(os.environ[k])
 
     try:
         if "MOZ_FETCHES" in os.environ:

src/taskgraph/transforms/run/__init__.py

@@ -330,7 +330,7 @@ def cmp_artifacts(a):
             "task-reference": json.dumps(task_fetches, sort_keys=True)
         }
 
-        env.setdefault("MOZ_FETCHES_DIR", "{task_workdir}/fetches")
+        env.setdefault("MOZ_FETCHES_DIR", "fetches")
 
         yield task
 

src/taskgraph/transforms/run/common.py

@@ -110,8 +110,7 @@ def support_vcs_checkout(config, task, taskdesc, repo_configs, sparse=False):
             "REPOSITORIES": json.dumps(
                 {repo.prefix: repo.name for repo in repo_configs.values()}
             ),
-            # If vcsdir is already absolute this will return it unmodified.
-            "VCS_PATH": path.join("{task_workdir}", vcsdir),
+            "VCS_PATH": vcsdir,
         }
     )
     for repo_config in repo_configs.values():
@@ -199,5 +198,5 @@ def support_caches(
             # If cache_dir is already absolute, the `.join` call returns it as
             # is. In that case, {task_workdir} will get interpolated by
             # run-task.
-            env[cache_cfg["env"]] = path.join("{task_workdir}", cache_dir)
+            env[cache_cfg["env"]] = cache_dir
         add_cache(task, taskdesc, cache_name, cache_dir)

test/test_scripts_run_task.py

@@ -13,6 +13,7 @@
 import pytest
 
 import taskgraph
+from taskgraph.util.caches import CACHES
 
 
 @pytest.fixture(scope="module")
@@ -468,21 +469,15 @@ def inner(extra_args=None, env=None):
     return inner
 
 
-def test_main_interpolate_environment(run_main):
-    result, env = run_main(
-        env={
-            "MOZ_FETCHES_DIR": "{task_workdir}/file",
-            "UPLOAD_DIR": "$TASK_WORKDIR/file",
-            "FOO": "{foo}/file",
-            "BAR": "file",
-        }
-    )
+def test_main_abspath_environment(run_main):
+    envvars = ["MOZ_FETCHES_DIR", "UPLOAD_DIR"]
+    envvars += [cache["env"] for cache in CACHES.values() if "env" in cache]
+    env = {key: "file" for key in envvars}
+    env["FOO"] = "file"
+
+    result, env = run_main(env=env)
     assert result == 0
 
-    assert env == {
-        "MOZ_FETCHES_DIR": "/builds/worker/file",
-        "UPLOAD_DIR": "$TASK_WORKDIR/file",
-        "FOO": "{foo}/file",
-        "BAR": "file",
-        "TASK_WORKDIR": "/builds/worker",
-    }
+    assert env.get("FOO") == "file"
+    for key in envvars:
+        assert env[key] == "/builds/worker/file"

test/test_transforms_run_run_task.py

@@ -114,7 +114,7 @@ def assert_generic_worker(task):
                 "HG_STORE_PATH": "y:/hg-shared",
                 "MOZ_SCM_LEVEL": "1",
                 "REPOSITORIES": '{"ci": "Taskgraph"}',
-                "VCS_PATH": "{task_workdir}/build/src",
+                "VCS_PATH": "build/src",
             },
             "implementation": "generic-worker",
             "mounts": [