_stream.py: Fetch sources while launching build shellschandan/build-shell-fetch

Part of https://gitlab.com/BuildStream/buildstream/-/issues/1068.

Make behavior of `shell` command similar to other commands that need
sources like `build`, `workspace open`, `source checkout` etc.

3 files changed, 47 insertions, 10 deletions

diff --git a/NEWS b/NEWS
index dcc9a60d3..ec6f5f352 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@
 (unreleased)
 ============
 
+CLI
+---
+
+  o `bst shell --build` will now automatically fetch missing sources.
+
 
 ==================
 buildstream 1.93.3
diff --git a/src/buildstream/_stream.py b/src/buildstream/_stream.py
index 09e6dfb17..48390ba14 100644
--- a/src/buildstream/_stream.py
+++ b/src/buildstream/_stream.py
@@ -205,13 +205,6 @@ class Stream:
         if unique_id and element is None:
             element = Plugin._lookup(unique_id)
 
-        # Assert we have everything we need built, using the element
-        # definitions to control the execution environment only.
-        if scope == Scope.BUILD and not element._has_all_sources_in_source_cache():
-            raise StreamError(
-                "Sources for element {} are not cached." "Element must be fetched.".format(element._get_full_name())
-            )
-
         missing_deps = [dep for dep in self._pipeline.dependencies([element], scope) if not dep._cached()]
         if missing_deps:
             if not pull_dependencies:
@@ -251,6 +244,11 @@ class Stream:
             else:
                 buildtree = True
 
+        # Ensure we have our sources if we are launching a build shell
+        if scope == Scope.BUILD and not buildtree:
+            self._fetch([element])
+            self._pipeline.assert_sources_cached([element])
+
         return element._shell(
             scope, mounts=mounts, isolate=isolate, prompt=prompt, command=command, usebuildtree=buildtree
         )
diff --git a/tests/integration/shell.py b/tests/integration/shell.py
index 7fa742f41..11aba87da 100644
--- a/tests/integration/shell.py
+++ b/tests/integration/shell.py
@@ -2,6 +2,8 @@
 # pylint: disable=redefined-outer-name
 
 import os
+import uuid
+
 import pytest
 
 from buildstream import _yaml
@@ -299,9 +301,6 @@ def test_workspace_visible(cli, datafiles):
     # Cat the hello.c file from a bst shell command, and assert
     # that we got the same content here
     #
-    result = cli.run(project=project, args=["source", "fetch", element_name])
-    assert result.exit_code == 0
-
     result = cli.run(project=project, args=["shell", "--build", element_name, "--", "cat", "hello.c"])
     assert result.exit_code == 0
     assert result.output == workspace_hello
@@ -400,3 +399,38 @@ def test_integration_partial_artifact(cli, datafiles, tmpdir, integration_cache)
         result = cli.run(project=project, args=["shell", "--pull", element_name, "--", "hello"])
         result.assert_success()
         assert "autotools/amhello.bst" in result.get_pulled_elements()
+
+
+# Test that the sources are fetched automatically when opening a build shell
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.skipif(not HAVE_SANDBOX, reason="Only available with a functioning sandbox")
+def test_build_shell_fetch(cli, datafiles):
+    project = str(datafiles)
+    element_name = "build-shell-fetch.bst"
+
+    # Create a file with unique contents such that it cannot be in the cache already
+    test_filepath = os.path.join(project, "files", "hello.txt")
+    test_message = "Hello World! {}".format(uuid.uuid4())
+    with open(test_filepath, "w") as f:
+        f.write(test_message)
+    checksum = utils.sha256sum(test_filepath)
+
+    # Create an element that has this unique file as a source
+    element = {
+        "kind": "manual",
+        "depends": ["base.bst"],
+        "sources": [{"kind": "remote", "url": "project_dir:/files/hello.txt", "ref": checksum}],
+    }
+    _yaml.roundtrip_dump(element, os.path.join(project, "elements", element_name))
+
+    # Ensure our dependencies are cached
+    result = cli.run(project=project, args=["build", "base.bst"])
+    result.assert_success()
+
+    # Ensure our sources are not cached
+    assert cli.get_element_state(project, element_name) == "fetch needed"
+
+    # Launching a shell should fetch any uncached sources
+    result = cli.run(project=project, args=["shell", "--build", element_name, "cat", "hello.txt"])
+    result.assert_success()
+    assert result.output == test_message