Logging: Replace tracing with an efficient logging implementation, with 0-runtime cost for disabled log levels. (https://www.pivotaltracker.com/story/show/183755412)
Profiling: Support submitting `profiler` events to the User Timing Web API, so that measurements can be viewed directly in the browser. (https://www.pivotaltracker.com/story/show/184003550)
# Important Notes
Logging interface:
- The macros (`warn!`, etc.) now take standard `format_args!` arguments (the tracing implementations accepted a broader syntax).
- Compile-time log levels can now be set through the CLI, like so:
`./run ide start --log-level=trace --uncollapsed-log-level=info`
Profiling:
- The hotkey Ctrl+Alt+Shift+P submits all `profiler` events logged since the application was loaded to the Web API, so that they can then be viewed with the browser's developer tools. Note that standard tools are not able to represent async task lifetimes or metadata; this is a convenient interface to a subset of `profiler` data.
- As an alternative interface, a runtime flag enables continuous measurement submission. In the browser it can be set through a URL parameter, like http://localhost:8080/?emit_user_timing_measurements=true. Note that this mode significantly impacts performance.
Implements https://www.pivotaltracker.com/n/projects/2539304/stories/184023445
Added a dropdown widget to graph node for all span tree nodes that have tag values present. When an option is selected, the controller receives a partial expression update, which targets specific crumbs of the expression (similar to how edge endpoint updates work).
https://user-images.githubusercontent.com/919491/210219931-8ae418fd-3ac4-44a5-abea-9e670f15cdf9.mp4
# Important Notes
Right now the dropdown widget is recreated every time the node is edited, including a dropdown option being selected. This causes it to close every time. I wanted to get around that by diffing span trees, but I wasn't able to do it in useful way. Additionally, current implementation of node input expression view heavily relies on being reinitialized from scratch every time. This led to more necessary changes than I was comfortable with for this task. I believe it will be easier to implement it as part of more complete widget support, especially after dynamic data support, as we will have proper widget type information.
Implements https://www.pivotaltracker.com/n/projects/2539304/stories/184023380
Dropdown component. Planned to be used in nodes as a single and multiple selection widget, both for static and dynamically loaded values. Initial support is focused on static data, with limited support for dynamic sources. Notably, loading states are not supported yet. Full support for that is planned to be added later with widget lazy-loading.
- Supports single and multiple selections.
- Dedicated API for providing a static list of all entries.
- Range-based query API for dynamically loading data as it is scrolled (only basic support - will need more work for proper async lazy-loading).
- Internal entry cache and query batching to avoid querying data one by one (the batching for now is very basic, will have to be improved for proper lazy-loading).
- Automatic dropdown width adjustment based on the entry label lengths, up to a set max allowed value.
- Open and close animation.
- Keyboard support for focusing and selecting entries.
![image](https://user-images.githubusercontent.com/919491/207866293-de2e3fef-c93b-48cc-8253-11c186d223fd.png)
# Important Notes
Implementing the dropdown on top of grid-view have uncovered some assumptions around grid-view layers. It was assumed to always be a part of the component browser. Removing that assumption required a mechanism for propagating camera update information through layer tree. This is now implemented using a `camera_parent` layer field. Ideally each layer should simply have at most a single parent, and camera inheritance would follow that. That refactor turned out to be quite involved, so right now the simpler temporary solution is introduced in order to not delay this PR further.
This is an enhancement of the `Slider` component implemented in #3852. It adds the following features:
* Tooltips and precision change hints
* Selectable slider limit behaviors
* Textual slider value editing
* Vertical slider layout
#### Tooltips
An information tooltip can now be added to a slider, it is shown when the mouse hovers over the component. Additionally, a pop-up indicating the slider's precision appears when the slider's precision has been adjusted.
https://user-images.githubusercontent.com/117099775/206148098-3b4dc059-18aa-4200-9ee0-5d4382363810.mp4
#### Slider limits
The previous slider implementation clamped the adjusted value to the slider's minimum/maximum limits. Now the following behaviors are available:
* Hard limits: Clamp the value to a range within the slider's limits.
* Soft limits: The value can extend beyond the slider's limits. When this occurs, an overflow indicator will be displayed on the side of the limit that is exceeded.
* Adaptive limits: The value can extend beyond the slider's limits. When this occurs, the exceeded limit will temporarily be adjusted to double the slider's range. This will be performed iteratively until the value falls within the extended limits. When a limit is extended and the value is adjusted to fit a smaller range, the extended limit will be iteratively halved until only the necessary range is covered. The slider's extended limits will never shrink to a range smaller than the original range.
These behaviors can be set to the lower and upper limits of a slider independently.
https://user-images.githubusercontent.com/117099775/206148139-6149c91d-ef49-4e2d-97f6-71084f52591c.mp4
#### Textual editing
The slider's value can now be entered through a text input field. Double-click to edit the slider's current value. To confirm the edit press `enter`, or press `escape` to cancel the edit. If an invalid value is entered on confirmation the slider will revert to its value before the edit. The slider's precision will be adjusted based on the number of decimal places of the value entered.
https://user-images.githubusercontent.com/117099775/206148170-d3fa4c82-6e73-4b1c-9be9-cb99979f7b70.mp4
#### Vertical layout
The slider component now supports a vertical layout. In this case value adjustment is performed by a vertical mouse movement, and a horizontal movement adjusts the slider's precision. The slider's track now fills the component in a vertical direction, and the slider's label is displayed near the top end of the component.
https://user-images.githubusercontent.com/117099775/206148211-0f176aaf-bc1b-45e2-afd7-0d28391aafcb.mp4
#### Scroll bar mode
The slider component supports two indicator modes:
* `Track`: The component is filled with a colored bar from the lower limit (empty) to the upper limit (full) dependent on the slider's value.
* `Thumb`: The component contains a rounded indicator that moves along the slider from one end to the other, indicating the slider's value proportionally to the slider's limits. The width of the indicator is configurable.
In addition, the value text, text entry, and precision adjustment can be turned off to provide a scroll bar appearance when used with the `Thumb` indicator.
https://user-images.githubusercontent.com/117099775/206148261-ae291073-85e9-4082-9f91-39b65fecdc0f.mp4
#### Example scene shortcuts
The example scene contains two shortcuts in order to evaluate the dynamic addition and removal of the slider components:
* `CTRL+D` drops all the slider components that are added to the scene.
* `CTRL+A` adds a new set of example slider components to the scene.
Fixes regression https://www.pivotaltracker.com/n/projects/2539304/stories/183895961
# Important Notes
The root cause of the issue was a missing deref before `flavor()` call. The autoderef doesn't work there, because the `ShapeSystemFlavorProvider` trait is implemented for all types, including `Ref`. We should reconsider if blanket default impl is a good idea, as this is a very scary footgun.
Apart from that, the cleanup of layer elements was not handling systems with same ID but different flavors correctly. That could cause text to disappear when given layer had text of multiple fonts, and all shapes of one of them got removed. Now the element is removed from layer only when all systems sharing given system ID have no more instances to render.
Fix issues noted here: https://github.com/enso-org/enso/pull/3678#issuecomment-1273623924
- Time complexity of an operation during line-redrawing scaled quadratically with number of lines in a change; now linear.
- Time complexity of adding `n` selections to a group was `O(n^2)`. Now it is `O(n log n)`, even if the selections are added one by one.
Also fix a subtle bug I found in `Group::newest_mut`: It returned a mutable reference that allowed breaking the *sorted* invariant of the selection group. The new implementation moves the element to invalidated space before returning a reference (internally to `LazyInvariantVec`), so that if it is mutated it will be moved to its correct location.
### Important Notes
New APIs:
- `NonEmptyVec::extend_at` supports inserting a sequence of elements at a location, with asymptotically-better performance than a series of `insert`s. (This is a subset of the functionality of `Vec::splice`, a function which we can't safely offer for `NonEmptyVec`).
- `LazyInvariantVec` supports lazily-restoring an invariant on a vector. For an invariant such as *sorted* (or in this case, *sorted and merged*), this allows asymptotically-better performance than maintaining the invariant with each mutation.
This `Slider` component allows adjusting a numeric value with the mouse. The value is increased or decreased by clicking on the component and dragging it to the left or right.
The `Slider` has a configurable default value. `Ctrl`+clicking on the component resets its value to that default. When the value is moved away from the default, the value is printed in **bold**.
The `Slider` precision is increased or decreased by clicking the component and dragging upward or downward. This precision influences how quickly the value changes when the mouse moves horizontally, the steps in which the value is incremented or decremented, and the number of digits used to display the value. There is a margin around the component within which the precision is not changed. Beyond this margin, the precision is increased or decreased in powers of 10 (e.g. `0.1` -> `0.01` -> `0.001` when moving the mouse downwards, or `0.1` -> `1.0` -> `10.0` when moving the mouse upwards). The margin and distance between consecutive steps along the vertical axis are configurable.
The value of the `Slider` is limited to a configurable range, and cannot be adjusted beyond that range. A colored bar fills the component to indicate the current value within the range.
#### Video demonstration
https://user-images.githubusercontent.com/117099775/202244982-2f6f419d-7281-41f6-8607-7e492ad25b46.mp4
#### Future additions
This is the first iteration of the `Slider` component. Additional features are planned for the future:
* Textual editing of the value.
* Improved visual feedback on precision changes.
* Additional out-of-range behaviors.
When hovering the mouse pointer over the Marketplace button on the left bar of the Component Browser, show a caption informing that the Marketplace will be available soon.
https://www.pivotaltracker.com/story/show/182613789
#### Visuals
The video below demonstrates the caption shown when hovering the Marketplace button on the left bar of the Component Browser. It shows the caption disappearing after a hardcoded time, or when the mouse pointer is moved away from the button.
https://user-images.githubusercontent.com/273837/196195809-45a712e1-ad86-47d8-99ff-1475a0b74c6e.mov
# Important Notes
- The "Label" visual component was fixed. Previously, the width calculation of the background was not synchronized correctly with the text width. As a result, a zero-width background was displayed when a Label was shown for the first time.
This PR introduced an overhauled Component List Panel implementation, making use of the efficient EnsoGL grid view component. Also, it delivers a couple of new features:
* A part of the new design: there are no more section headers in grid, instead groups are "glued" together. The local scope section is under "popular" (old "favorites").
* The keyboard management inside grid works.
* there is a mouse hover highlight
* selecting the lowest entry in section when jumping with navigation bar.
* accepting input as-is with cmd/ctrl + Enter.
https://user-images.githubusercontent.com/3919101/194561890-fffb9b41-2f0d-4357-8d9a-5038a6bcb023.mp4
### Important Notes
**What is not implemented:**
* [Focus management between panels.](https://www.pivotaltracker.com/story/show/180872763) The grid is always focused. To accept the current input, use ctrl+Enter shortcut.
* [Proper handling of selection when having empty space on the right and pressing right arrow.](https://www.pivotaltracker.com/story/show/183487880)
* When entering a module, its name is not added to the input as described in the design doc. Will be a part of [this User Story](https://www.pivotaltracker.com/story/show/181058321).
**Known issues**
* [the selection, especially in the local scope section, has sometimes an undesirable offset](https://www.pivotaltracker.com/story/show/183487730). The cause is known, but not so easy to fix.
* The inserted nodes are often producing errors. The Browser's inherits the outdated understanding of the language from old Node Searcher, and it does not include new form of imports, static methods etc. Those all will be fixed as a part of [this User Story](https://www.pivotaltracker.com/story/show/181058321).
* The performance is improved, but still not ideal, due to problems in [text areas](https://www.pivotaltracker.com/story/show/183406745).
* To scroll the documentation panel, you must first click on it.
[ci no changelog needed]
[Task link](https://www.pivotaltracker.com/story/show/182675703)
This PR implements the actual integration of the breadcrumbs panel with the component list panel. A special breadcrumbs controller (`controller::searcher::breadcrumbs`) is tracking the currently opened module with a list of its parents. The searcher presenter uses the API of the controller to sync the displayed list of breadcrumbs with the controller state.
https://user-images.githubusercontent.com/6566674/193064122-7d3fc4d6-9148-4ded-a73e-767ac9ac83f8.mp4
# Important Notes
- There is an `All` breadcrumb displayed at all times at the beginning of the list. It will be replaced with a section name as part of [Section Title on Component Browser's Breadcrumbs Panel](https://www.pivotaltracker.com/story/show/182610561) task.
- I changed the implementation of `project::main_module_id`, `project::QualifiedName::main_module`, and `API::main_module` so that they are logically connected which each other.
- I adjusted the Breadcrumbs View to avoid "appearance" animation glitches when opening new modules. `set_entries` was replaced with the `set_entries_from` endpoint.
When a GridView is navigated using the keyboard, scroll it to display the newly selected entry.
https://www.pivotaltracker.com/story/show/182593635
#### Visuals
See below for a video demonstrating automatic scrolling of the GridView when arrow keys are pressed on the keyboard. The first video below shows the default scrolling behavior in a GridView without headers.
Note:
- When the Grid View is scrolled, the mouse hover highlight moves away from the mouse position. This is not a new regression, the behavior is the same in the `develop` branch (e.g. when scrolling using the mouse).
https://user-images.githubusercontent.com/273837/190183984-91f7808c-3606-43f8-bcda-ac4d5f84e00f.mov
The video below shows the behavior in a GridView with headers when the GridView is first scrolled to its top-left corner. The following guidance from the Design Doc is enabled and showcased:
> Users can change the selected component by pressing the arrow keys. The Focus does not move up if it does not have to (in most cases, the focus is located in the second row from the bottom). Instead, the component list scrolls down if there are enough entries.
https://user-images.githubusercontent.com/273837/189151546-e50aaf22-6f4d-41cb-809f-60038305745f.mov
The next video shows the behavior in the same GridView as in the previous example when the GridView is first scrolled away from any of its boundary entries. Notably, scrolling happens only when the selection is moved using the keyboard arrow keys, not when changing the selection using the mouse. This behavior is based on a discussion with @wdanilo on Discord.
https://user-images.githubusercontent.com/273837/189151974-d992be93-f61f-4e9f-9f4c-dfe260bbec5b.mov
This PR contains an entry definition for Grid View to be used inside Component List Panel View. The Example grid view with the entry definition may be seen on new_component_list_panel_view debug scene.
https://user-images.githubusercontent.com/3919101/190663278-23c35ab0-f426-4001-8128-df7147aafb9e.mp4
# Important Notes
* The styling is not detailed yet due to time constraints (I want to move to integration this grid view to Component Panel List ASAP) and the fact that I could not get new mplus1 font working with text Area.
* Implementing this required adding a "contour offset" feature to the Grid View.
[ci no changelog needed]
[Task link](https://www.pivotaltracker.com/story/show/181445628).
This PR implements a Breadcrumbs panel for the new component browser.
The Breadcrumbs is a horizontal list of text labels separated by a special icon and has an optional ellipsis icon at the end.
It is implemented using the new GridView component.
Video:
Demo of adding new breadcrumbs, scrolling behavior, and selecting breadcrumbs with the mouse.
https://user-images.githubusercontent.com/6566674/189199432-77807cef-00dc-4abe-b95c-b17a536f59f6.mp4
Demo of selecting breadcrumbs with keyboard shortcuts:
https://user-images.githubusercontent.com/6566674/189199603-53e55335-73ba-4ed7-8291-4455144c06aa.mp4
# Important Notes
- This PR implements an old interaction of the design of the component browser. The new design of the breadcrumbs can not be easily integrated into the current look of the component browser, so we would need to update styles later. It should be a relatively simple task. *The implementation uses color from the new design though. (but not fonts and sizes)*
- I found a bug in the grid view implementation that causes panics at runtime in some conditions. The reason is triggering FRP endpoints while constructing new entries. This issue is fixed in the PR.
Add support for moving the selection in a Grid View using the keyboard.
https://www.pivotaltracker.com/story/show/182585789
#### Visuals
See below for videos showcasing GridView selection keyboard navigation in the `grid_view` debug scene. In the videos, messages in the Developer Console can be observed. When a keypress would result in the selection being moved out of the GridView, the selection is not moved and a message is emitted in the Developer Console instead, showcasing an FRP output signal emitted on such event. Please note that the videos are recorded with the tracing level changed to `DEBUG`. In a default build, the tracing level is set to `WARN`, and the messages visible in the videos are not displayed in the Developer Console.
https://user-images.githubusercontent.com/273837/188483972-89d79f7b-1303-457b-869f-282e0809a755.movhttps://user-images.githubusercontent.com/273837/188484294-e9b6461c-a84f-4817-9447-d792f2ebdbb5.mov
The following video shows moving the selection between "regular" entries and header entries. It also shows a current usability limitation of the selection keyboard navigation feature, such that the Grid is not scrolled when the selection leaves the visible part of the Grid, and the selection may thus disappear from view.
https://user-images.githubusercontent.com/273837/188485238-29a82b27-de2f-4cf8-a2e7-ff8c3f41478d.mov
# Important Notes
- Keyboard navigation only works when a GridView has focus.
- Selection keyboard navigation only works if the selection was already set to some entry beforehand.
- If keyboard navigation would move selection outside of the grid, the selection movement is canceled and an FRP event is emitted.
[ci no changelog needed]
[Task link](https://www.pivotaltracker.com/story/show/182955595)
This PR implements variable column widths in the new Grid View component. We need this feature to quickly implement various parts of the UI, including the breadcrumbs panel of the component browser.
There are two ways to change the width of the specific column:
1. "From the outside", using the `set_column_width` endpoint of the Grid View
2. "From the inside", using the `override_column_width` endpoint of the EntryFrp.
Both ways work similarly, but the latter is helpful for our breadcrumbs implementation, as it allows for entry to decide on the width of the column by its content.
See the screencast with three grid views. The top-left one has every even column shrunk by GridView API. Every grid view has a second column extended by EntryFrp API.
https://user-images.githubusercontent.com/6566674/185060985-7b7df076-c659-41fa-977a-22875493f8d4.mp4
This PR adds a new variant of selection, where the mouse-hovered entry is highlighted and may be selected by clicking.
In the video below, we have three grid views with slightly different settings:
* In the left-top corner, both hover and selection highlight is just a shape under the label. Such a grid view does not require additional layers (when compared to non-selectable grid view).
* In the left-bottom corner the hover is normal shape, but selection is a _masked layer_ which allows us to have different text color. This setting requires three more layers to render.
* In the right-top corner, both hover and selection are displayed in the masked layer, creating 6 additional layers.
https://user-images.githubusercontent.com/3919101/181514178-f243bfeb-f2dd-4507-adc3-5344ae0579b7.mp4
**Note**: This PR also contains content of previous Grid View PR. We decided to discard the previous, because this one did some refactoring of old one, and it's not a big addition.
Added a scrollable::GridView component, which just embeds the GridView in ScrollArea. Also, re-worked the idea of text layers.
https://user-images.githubusercontent.com/3919101/179020359-512ee127-c333-4f86-bff5-f1cb4154e03c.mp4
This PR contains all work for finishing integration of first Component List Panel in the IDE:
* It adds a stub for the whole Component Browser View. The documentation panel is re-used from the old searcher.
* It has the presenter implementation, integrating the view with Hierarchical Component List from the controller.
* It extends the View API, so the integration is possible, making use of Component Group Set wrapper.
* The selection integration was also merged into this PR, because it depended on the API extension mentioned above. However, we should avoid such practice in the future.
https://user-images.githubusercontent.com/3919101/177816427-8c4285b4-8941-4048-a400-52f4acf77a9f.mp4
# Important Notes
There are some known issues, to-be-fixed in the future.
* The performance is bad. It should be improved with new text::Area, and the decent one shall come with [GridView inside component browser](https://www.pivotaltracker.com/story/show/182561072)
* There is no keyboard navigation. It should also be delivered with [GridView](https://www.pivotaltracker.com/story/show/182561072).
* The Favorites section is not [filtered out by node source type](https://www.pivotaltracker.com/story/show/182661634).
[Task link](https://www.pivotaltracker.com/story/show/182194574).
[ci no changelog needed]
This PR implements a new selection box that will replace an old (not really working) one in the component browser. The old selection box wasn't working well with the headers of the component groups, so we were forced to make a much harder implementation.
The new implementation duplicates some visual components and places them in a separate layer. Then, a rectangular mask cuts off everything that is not "selected". This way:
- We have more control over what the selected entries should look like.
- We can easily support the multi-layer structure of the component groups with headers.
- We avoid problems with nested masks that our renderer doesn't support at the moment.
To be more precise, we duplicate the following:
- Background of the component group becomes the "fill" of the selection.
- Entries text and icons - we can alter them easily.
- Header background and header text. By placing them in separate scene layers we ensure correct rendering order.
https://user-images.githubusercontent.com/6566674/173657899-1067f538-4329-44f9-9dc2-78c8a4708b5a.mp4
# Important Notes
- This PR implements the base of our future selection mechanism, selecting entries with a mouse and keyboard still has several issues that will be fixed in the future tasks.
- The scrolling behavior will also be improved in future tasks. Right we only restrict the selection box position so that it never leaves the borders of the component group.
- I added a new function to `add` shapes to new layers in a non-exclusive way (we had only `add_exclusive`) before. I have no idea how we didn't use this feature before even though we mention it a lot in the docs.
- The demo scene restricts the position of the selection box for one-column component groups but does not for the wide component group.
[ci no changelog needed]
This PR implements a new helper for the future Component Browser - `component_group::multi::Wrapper`. It propagates FRP events from multiple component groups and ensures that only a single component group is focused at all times.
See the updated component group demo scene (console logs shows propagated FRP events from all component groups):
https://user-images.githubusercontent.com/6566674/172359141-8ea6f1ba-e357-4c1b-852a-adb4d5207e03.mp4
- Fixed a `define_endpoints_2!` macro. FRP endpoints for `focus` events weren't connected properly.
- List View now uses an overlay shape to catch mouse events, it allows much easier implementation of `is_header_selected` in the component group.
Define some workflows for batch-mode profiling.
Implemented:
- collapse nodes
- create node
- enter collapsed node
- new project
- open visualization
They can currently be built and run with a command like:
`./run.sh ide build --profiling-level=debug && dist/ide/linux-unpacked/enso --entry-point profile --workflow create_node --save-profile out.json`
And the data can be displayed with:
`dist/ide/linux-unpacked/enso --entry-point profiling_run_graph --load-profile out.json`
Demo of recording and viewing a profile with a command-line one-liner:
https://user-images.githubusercontent.com/1047859/169954795-2d9520ca-84f9-45d2-b83a-5063ebe6f718.mp4
See: https://www.pivotaltracker.com/story/show/182195399.
# Important Notes
- When defining workflows, two helpers are enough to allow us to tell when the action is really done: `Fixture::compile_new_shaders`, and `Fixture::backend_execution`. Often, it is appropriate to await both, but it depends on the task.
- The shader compiler is now driven by a `Controller`; while the `Compiler` is reset if context is lost, the `Controller`'s state survives context loss.
- A new `--load-profile` option supports specifying a profile by path when running `profiling_run_graph`.
- Drop the `with_same_start` profiler interface; we ended up preferring a child profiler convention, and this interface was not implemented compatibly with the stricter data model we've had since the introduction of `profiler::data`.
- Fix the noisy `rustfmt` output.
This PR extends the Component Group Entry with icon and option to highlight the text. Here the convert has highlighted "con".
https://user-images.githubusercontent.com/3919101/169046537-4f8b823c-322e-40dc-8abb-24d1d7092341.mp4
### Important Notes
Although this PR includes effort for adjusting Component Group style to better reflect the design, it is not entirely finished: the selection still works badly and will be fixed in another PR.
[ci no changelog needed]
[Task link](https://www.pivotaltracker.com/story/show/181725003)
This PR implements a fully visible component group header while scrolling the group (using the ScrollArea).
The header moves in sync with scrolling movements (using new `set_header_pos` FRP input), so it looks like the component group is scrolled. ScrollArea masks the "scrolled" entries above the header. This design allows a fully visible header even though our renderer doesn't support nested layers masking yet.
The screencast:
https://user-images.githubusercontent.com/6566674/168320360-2c2017b2-0ef5-42ce-9c79-82b9641c1d73.mp4
The most recent one, with the updated demo scene from develop:
https://user-images.githubusercontent.com/6566674/168555268-8552c4b0-f887-4388-89a1-e65ddf668be6.mp4
# Important Notes
- I fixed the API of the list view so now it supports non-hardcoded scene layers (previously it did not). I also believe it was implemented incorrectly.
- I've found a [pretty weird bug](https://www.pivotaltracker.com/story/show/182193824): the component group inside the ScrollArea is invisible unless I add some arbitrary shape to the scroll area content. I use a `transparent_circle` for this purpose in the demo scene. The bug is probably related to masking the sublayers, though I wasn't able to reproduce it properly on a simpler example.
- The selection box is removed from the demo scene as agreed with @farmaazon . The correct implementation has proven to be much harder than I expected, and we will implement another approach in a separate PR.
- I also modified the `shadow::Parameters` so that it uses `Var`s instead of plain values.