Add pip cell installs to dependency graph (#1698)

## Changes
Logic for registering import installed in a pip cell

### Linked issues
#1642
Follow up on #1692

### Functionality 

- [ ] added relevant user documentation
- [ ] added new CLI command
- [ ] modified existing command: `databricks labs ucx ...`
- [ ] added a new workflow
- [ ] modified existing workflow: `...`
- [ ] added a new table
- [ ] modified existing table: `...`

### Tests
<!-- How is this tested? Please see the checklist below and also
describe any other relevant tests -->

- [ ] manually tested
- [ ] added unit tests
- [ ] added integration tests
- [ ] verified on staging environment (screenshot attached)

src/databricks/labs/ucx/source_code/graph.py

@@ -80,6 +80,7 @@ def register_dependency(self, dependency: Dependency) -> MaybeGraph:
         child_graph = DependencyGraph(dependency, self, self._resolver, self._path_lookup)
         self._dependencies[dependency] = child_graph
         container = dependency.load(self.path_lookup)
+        # TODO: Return either (child) graph OR problems
         if not container:
             problem = DependencyProblem('dependency-register-failed', 'Failed to register dependency', dependency.path)
             return MaybeGraph(child_graph, [problem])

src/databricks/labs/ucx/source_code/notebooks/cells.py

@@ -182,9 +182,18 @@ def language(self):
     def is_runnable(self) -> bool:
         return True  # TODO
 
-    def build_dependency_graph(self, _: DependencyGraph) -> list[DependencyProblem]:
+    def build_dependency_graph(self, graph: DependencyGraph) -> list[DependencyProblem]:
         # TODO: https://github.com/databrickslabs/ucx/issues/1642
-        return []
+        # TODO: this is very basic code, we need to improve it
+        splits = self.original_code.split(' ')
+        if len(splits) < 3:
+            return [DependencyProblem("library-install-failed", f"Missing arguments in '{self.original_code}'")]
+        if splits[1] != "install":
+            return [DependencyProblem("library-install-failed", f"Unsupported %pip command: {splits[1]}")]
+        # TODO: we need to support different formats of the library name and etc
+        library = splits[2]
+
+        return graph.register_library(library)
 
 
 class CellLanguage(Enum):

tests/unit/source_code/notebooks/test_cells.py

@@ -0,0 +1,88 @@
+from pathlib import Path
+from unittest.mock import create_autospec
+
+from databricks.labs.ucx.source_code.graph import Dependency, DependencyGraph, DependencyResolver
+from databricks.labs.ucx.source_code.files import FileLoader
+from databricks.labs.ucx.source_code.notebooks.cells import CellLanguage, PipCell
+from databricks.labs.ucx.source_code.notebooks.loaders import (
+    NotebookResolver,
+    NotebookLoader,
+)
+from databricks.labs.ucx.source_code.site_packages import PipResolver
+
+
+def test_pip_cell_language_is_pip():
+    assert PipCell("code").language == CellLanguage.PIP
+
+
+def test_pip_cell_build_dependency_graph_invokes_register_library():
+    graph = create_autospec(DependencyGraph)
+
+    code = "%pip install databricks"
+    cell = PipCell(code)
+
+    problems = cell.build_dependency_graph(graph)
+
+    assert len(problems) == 0
+    graph.register_library.assert_called_once_with("databricks")
+
+
+def test_pip_cell_build_dependency_graph_pip_registers_missing_library():
+    graph = create_autospec(DependencyGraph)
+
+    code = "%pip install"
+    cell = PipCell(code)
+
+    problems = cell.build_dependency_graph(graph)
+
+    assert len(problems) == 1
+    assert problems[0].code == "library-install-failed"
+    assert problems[0].message == "Missing arguments in '%pip install'"
+    graph.register_library.assert_not_called()
+
+
+def test_pip_cell_build_dependency_graph_reports_incorrect_syntax():
+    graph = create_autospec(DependencyGraph)
+
+    code = "%pip installl pytest"  # typo on purpose
+    cell = PipCell(code)
+
+    problems = cell.build_dependency_graph(graph)
+
+    assert len(problems) == 1
+    assert problems[0].code == "library-install-failed"
+    assert problems[0].message == "Unsupported %pip command: installl"
+    graph.register_library.assert_not_called()
+
+
+def test_pip_cell_build_dependency_graph_reports_unknown_library(mock_path_lookup):
+    dependency = Dependency(FileLoader(), Path("test"))
+    notebook_loader = NotebookLoader()
+    notebook_resolver = NotebookResolver(notebook_loader)
+    dependency_resolver = DependencyResolver(notebook_resolver, [PipResolver()], mock_path_lookup)
+    graph = DependencyGraph(dependency, None, dependency_resolver, mock_path_lookup)
+
+    code = "%pip install unknown-library-name"
+    cell = PipCell(code)
+
+    problems = cell.build_dependency_graph(graph)
+
+    assert len(problems) == 1
+    assert problems[0].code == "library-install-failed"
+    assert problems[0].message.startswith("Failed to install unknown-library-name")
+
+
+def test_pip_cell_build_dependency_graph_resolves_installed_library(mock_path_lookup):
+    dependency = Dependency(FileLoader(), Path("test"))
+    notebook_loader = NotebookLoader()
+    notebook_resolver = NotebookResolver(notebook_loader)
+    dependency_resolver = DependencyResolver(notebook_resolver, [PipResolver()], mock_path_lookup)
+    graph = DependencyGraph(dependency, None, dependency_resolver, mock_path_lookup)
+
+    code = "%pip install pytest"
+    cell = PipCell(code)
+
+    problems = cell.build_dependency_graph(graph)
+
+    assert len(problems) == 0
+    assert graph.path_lookup.resolve(Path("pytest")).exists()