[PR] Use display_name tag for @config.when nodes in visualizations [hamilton]

["digit50 (via GitHub)" <gi...@apache.org>]

digit50 opened a new pull request, #1766:
URL: https://github.com/apache/hamilton/pull/1766

   closes https://github.com/apache/hamilton/issues/1761
   
   Nodes built from `@config.when` or `@config.when_not` functions ignored their `display_name` tag in visualizations. `create_graphviz_graph` rebuilt their label as `f"{n.name}: {config_key}"` and passed it as the explicit `name` to `_get_node_label`, which gives that argument priority over the tag, so these nodes always showed as `a: mode` instead of `Pretty A: mode`.
   
   ## Changes
   
   - `hamilton/graph.py`: moved the `display_name` tag lookup (including the existing "list means first element" handling) out of `_get_node_label` into a small `_get_display_name` helper inside `create_graphviz_graph`. `_get_node_label` uses it when no explicit name is given, as before.
   - The config-node label is now built as `f"{_get_display_name(n)}: {config_key}"`, so the tag is used and the config suffix is kept. Nodes without the tag still get `<node name>: <config keys>`.
   
   ## How I tested this
   
   - Added `test_create_graphviz_graph_display_name_on_config_nodes` in `tests/test_graph.py`. It builds a graph from a `@config.when` function with `@tag(display_name=...)` on the outside and a `@config.when_not` function with the tag on the inside, and asserts that the Digraph source contains `<b>Pretty A: mode</b>` and `<b>Pretty C: mode</b>` and no longer contains `<b>a: mode</b>` or `<b>c: mode</b>`. It fails on main and passes with this change.
   - Ran `tests/test_graph.py`, `tests/function_modifiers` and `tests/plugins/test_polars*.py` before and after the change. The only failures are the same on both sides and come from my local environment (no Graphviz `dot` binary for the render tests, polars 2.x and a missing `xlsxwriter` for the polars plugin tests).
   - Ran the reproduction script from the issue: `display_all_functions()` and `visualize_execution()` now both show `Pretty A: mode`, `Pretty C: mode` and `Pretty D`.
   - `ruff check` and `ruff format --check` pass on the changed files.
   
   ## Notes
   
   No change to the explicit `name` override in `_get_node_label`; it still takes priority over the tag, so materializer and other callers behave as before.
   
   ## Checklist
   
   - [x] PR has an informative and human-readable title (this will be pulled into the release notes)
   - [x] Changes are limited to a single goal (no scope creep)
   - [x] Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
   - [x] Any _change_ in functionality is tested
   - [x] New functions are documented (with a description, list of inputs, and expected output)
   - [ ] Placeholder code is flagged / future TODOs are captured in comments
   - [ ] Project documentation has been updated if adding/changing functionality.
   


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