Feature/list viewer 1399 by Fred-Wu · Pull Request #1741 · REditorSupport/vscode-R

Fred-Wu · 2026-09-20T12:17:48Z

Closes #1399
Closes #1687
Closes #1576

Summary

Adds dedicated viewers for R lists and vectors, allowing large and deeply nested objects to be inspected without serialising the complete object when the viewer opens.

List Viewer

View() opens lists, environments, and S4 objects in a dedicated List Viewer.
Each child is shown with its name/index and a compact str() summary.
Nested list-like objects can be expanded directly in the viewer.
Viewable children have a View button:
- data frames and matrices open in the Data Viewer;
- nested lists, environments, and S4 objects open in the List Viewer;
- atomic vectors open in the Vector Viewer;
- other objects continue to use the existing object viewer.
Nested viewer titles preserve the R access path using $name, [[index]], and @slot as appropriate.
Atomic vectors open in a paged List Viewer rather than being fully converted to text.
Values are displayed vertically with their indices or names.
Vector values use the same formatting as Data Viewer cells.
Vector values are retrieved from the R session in pages, avoiding deparse() of large vectors.
This also allows large atomic columns from ordinary R data frames to be inspected without serialising the complete column.

Nested navigation

Nested List Viewer, Vector Viewer, and Data Viewer views remain associated with their top-level object, with separate viewer instances for each viewer type.
Adds Back navigation to return to the previous list view.
Adds breadcrumb navigation to move directly to a parent object.
Returning to a top-level data frame restores its Data Viewer rather than displaying it in the List Viewer.
Repeated View() calls for descendants of the same top-level object reuse the corresponding viewer.
List Viewer and Data Viewer panels use distinct icons.

On-demand loading

List contents, nested children, and vector values are retrieved from the R session on demand rather than serialising the complete object when the viewer opens.
Large lists and vectors are paged, with 500 entries retrieved at a time.
Only requested list entries are evaluated, preserving protection against evaluating unrequested or active bindings.

Session-aware viewers

List Viewer and Data Viewer remain associated with the R session that created them.
Viewer requests continue to use their originating session when switching sessions or reconnecting.
Closing one session does not affect viewers belonging to other sessions.

Viewer lifecycle fixes

Added state_generation to viewer state so delayed disposal requests cannot remove a newer viewer state that reused the same view_id.
Added documentGeneration to List Viewer and Data Viewer webview requests/responses so messages from a previous webview document are ignored after the panel is reloaded.
Renamed the lifecycle counters to distinguish R-side viewer state (state_generation) from webview document lifetime (documentGeneration).
Updated affected sess tests to use the new plot_backend argument and the required state_generation when disposing viewer state.

Tests

Adds regression coverage for:

structured and non-structured workspace children;
paged list and vector inspection;
stable child indices across pages;
nested expansion and navigation;
parent and back navigation;
restoring a top-level data frame to its Data Viewer;
reuse of List Viewer and Data Viewer panels;
session isolation and reconnect behaviour;
distinct List Viewer and Data Viewer icons;
vector formatting and supported S3/S4 values;
preservation of custom extraction semantics;
avoiding full vector serialisation;
avoiding evaluation of unrequested and active bindings;
stale viewer disposal after replacement state is created;
stale Data Viewer requests and responses after a webview reload.

Fred-Wu · 2026-09-20T12:33:20Z

I will leave this to 3.x milestone.

Here is the current behavior.

Screen.Recording.2026-10-03.at.7.03.23.pm.mov

renkun-ken

I reproduced five issues in revision 34bf0c134386187927c20eba6f7aa638ad8ae7f3: repeated evaluation of active root bindings, incorrect reconstruction of custom $ expressions, missing parent breadcrumbs when opening vectors from the List Viewer, loss of named-vector element names, and unbounded expansion of scalar POSIXlt values. The inline comments include reproduction details and suggested fixes.

Validation: TypeScript compilation, ESLint, 17 webview tests, and 212 R assertions passed. Targeted reproductions exposed these gaps; comparisons against the base revision confirmed the previous behavior for active bindings, custom $ extraction, named vectors, and POSIXlt values.

renkun-ken · 2026-10-04T01:30:58Z

+    }
+    if (!is.symbol(expression)) return(NULL)
+    name <- as.character(expression)
+    root <- listview_state(get(name, envir = envir, inherits = TRUE), name, owner)


[P2] Avoid evaluating the root binding twice

View(x) first forces x to determine its viewer type, then this get() evaluates the binding again. An active binding returning list(value = counter) runs twice, and the viewer displays the second value. The base revision evaluates it once. Reuse the evaluated argument, or skip breadcrumb reconstruction when it would force an active binding again.

renkun-ken · 2026-10-04T01:30:58Z

+      value <- expression[[3L]]
+      if (operator %in% c("$", "@") && is.symbol(value)) value <- as.character(value)
+      if (length(value) != 1L || !(is.character(value) || is.numeric(value))) return(NULL)
+      selectors <- c(list(list(kind = "index", value = value)), selectors)


[P2] Preserve the original extraction operator

Every expression selector becomes an index selector, so View(x$a) reconstructs its value using x[[index]]. For an S3 list class with a custom $ method, these can return different objects: I reproduced View(x$a) displaying 1 although x$a returns 42. Preserve the extraction semantics or fall back to the evaluated argument when the reconstructed value differs.

renkun-ken · 2026-10-04T01:30:58Z

+  if (listview_is_list(location$data)) {
+    return(listview_navigation(state, c(path, list(index))))
+  }
+  workspace_show_view(location$data, location$title, state$owner %||% state$title)


[P2] Retain parent breadcrumbs when opening vectors

For x <- list(a = list(values = 1:3)), opening values through the List Viewer calls workspace_show_view without context. The Vector Viewer consequently retains only the vector, with path [] and one breadcrumb labelled x$a$values. Users cannot navigate to a or x. Pass the retained root and descendant path, as the workspace entry point does.

renkun-ken · 2026-10-04T01:30:58Z

+      label <- if (!is.null(view_id) && isTRUE(vector_view)) {
+        paste0("[", index, "]")


[P2] Preserve named vector element names

View(c(one = 1, two = 2)) now displays only [1] and [2]. child_name is available here but discarded, while scalar extraction also removes the name from the displayed value. The previous viewer preserved both names. Include element names alongside their indices so named vectors remain interpretable.

renkun-ken · 2026-10-04T01:30:58Z

+      if (!is.null(view_id)) {
+        list(
+          label = label, str = summary, viewable = !isTRUE(vector_view), index = index,
+          has_children = !isTRUE(vector_view) && workspace_child_count(child) > 0L


[P2] Terminate expansion for scalar POSIXlt values

View(as.POSIXlt(c('2025-01-01', '2025-01-02'))) produces expandable timestamp rows. POSIXlt is internally a list, but scalar[[1]] returns an equivalent scalar, so each expansion creates another identical expandable row indefinitely. The previous viewer showed finite timestamp values. Treat POSIXlt elements as leaves or route them through a value formatter.

Fred-Wu · 2026-10-04T01:36:24Z

I reproduced five issues in revision 34bf0c134386187927c20eba6f7aa638ad8ae7f3: repeated evaluation of active root bindings, incorrect reconstruction of custom $ expressions, missing parent breadcrumbs when opening vectors from the List Viewer, loss of named-vector element names, and unbounded expansion of scalar POSIXlt values. The inline comments include reproduction details and suggested fixes.

Validation: TypeScript compilation, ESLint, 17 webview tests, and 212 R assertions passed. Targeted reproductions exposed these gaps; comparisons against the base revision confirmed the previous behavior for active bindings, custom $ extraction, named vectors, and POSIXlt values.

Thanks @renkun-ken. Some of those are being addressed right now.

renkun-ken

Reviewed the latest revision, 5c807f67be2d5d3609b88ba6d47b428923ade087. Four previous findings are fixed: the active-binding, custom-extraction, vector-breadcrumb, and POSIXlt reproductions now pass.

Two issues remain: named vectors still lose their element names, and difftime vectors lose their units during scalar extraction. The inline comments describe the remaining behavior and suggested fixes.

Validation: build, TypeScript compilation, ESLint, 27 viewer tests (including nine VS Code panel and session-ownership tests), and 417 R assertions passed. Targeted reproductions confirmed the two display issues; the base revision preserved duration units.

renkun-ken · 2026-10-04T05:41:54Z

+      label <- if (vector_rows) {
+        paste0("[", index, "]")


[P2] Named vectors still lose their names

The previous finding remains unresolved: View(c(one = 1, two = 2)) displays only [1] and [2], with values 1 and 2. child_name is available but discarded. Include names alongside indices so users can interpret named vectors.

renkun-ken · 2026-10-04T05:41:54Z

+      child <- switch(kind,
+        name = get(child_name, envir = object, inherits = FALSE),
+        slot = methods::slot(object, child_name),
+        index = object[[index]]


[P2] Preserve difftime units when formatting values

Extracting object[[index]] strips the difftime class and units before formatting. View(as.difftime(c(1, 2), units = 'hours')) and the equivalent vector in minutes both display identical bare values 1 and 2. The base revision preserved units. Use a class-preserving slice for vector formatting or explicitly include duration units.

renkun-ken

Reviewed revision 90ad9c34797333331799a18a554b6cd0aac5da64. All previous findings are resolved: active bindings are evaluated once, custom extraction displays the evaluated value, vector navigation retains parent breadcrumbs, named vectors retain their labels, POSIXlt expansion terminates, and difftime values retain their units. The original targeted reproductions now pass.

I found no remaining blocking issues. There is one nonblocking test correction inline: the pending table-request test needs to include the document generation so it reaches the asynchronous disposal path.

Validation: TypeScript compilation, ESLint, build, 28 viewer tests (including 10 VS Code panel/session tests), and 819 R assertions passed. I also reran the 10 panel/session tests with the missing generation field added in the temporary review checkout; they passed.

renkun-ken · 2026-10-04T13:45:31Z

+            const listener = receive.firstCall.args[0] as (message: unknown) => Promise<void>;
+            // With no R session, requests settle asynchronously with an unavailable response.
+            const pending = source === 'table'
+                ? [listener({ message: 'dataview/request', action: 'page', requestId: 1 })]


[P3] Include the document generation in the pending table request

The table request omits documentGeneration, so attachDynamicDataViewBridge rejects it at its new validation guard before calling sessionRequest. This makes the table version of the panel-close test pass without exercising a pending request during disposal. Add the captured documentGeneration to this message, as the list branch already does, so the test covers the intended race. I verified that the panel/session tests still pass with this field included.

eitsupi

ChatGPT review found one remaining concern: this PR changes the sess IPC contract for list/data viewers, but protocol_version is still 1.

Since old/new extension and sess combinations are no longer compatible for these messages, I think this should bump the protocol version and update the sess protocol documentation accordingly.

Also, the existing non-blocking comment about adding documentGeneration to the pending table-request test looks worth fixing at the same time.

eitsupi

ChatGPT review: small nit — do we need to vendor these Codicon SVGs?

Since these are built-in VS Code icons, it might be cleaner to use ThemeIcon for the panel icon and @vscode/codicons inside the webview instead of committing copies of the SVGs and maintaining their attribution separately.

Not blocking, but I think using the standard Codicon assets would be simpler and more theme-friendly.

Fred-Wu · 2026-10-04T16:07:39Z

ChatGPT review: small nit — do we need to vendor these Codicon SVGs?

Since these are built-in VS Code icons, it might be cleaner to use ThemeIcon for the panel icon and @vscode/codicons inside the webview instead of committing copies of the SVGs and maintaining their attribution separately.

Not blocking, but I think using the standard Codicon assets would be simpler and more theme-friendly.

Good point. There is no strong reason to vendor the SVGs. I'll switch the icons to use @vscode/codicons directly where possible. However, the codicon CSS and font used in the webview are still bundled from the package as support for Tab 's original UriIcon with ThemeIcon seems only announced from VS Code 1.110.

Maybe we should add a third-party notice in the source to cover those assets and the R icon.

renkun-ken

Reviewed revision 109dc25d8399e2227197f62bac9a0207967e868a. The pending-request test correction is fixed, the protocol-2 contract is documented, and the packaged Codicons CSS, font, and licenses are included in the generated VSIX. The previous viewer reproductions still pass, including named vectors and duration units.

One upgrade issue remains: protocol 2 is required, but the bundled sess package still has the same version as the protocol-1 package. The version-only installation checks therefore skip the update. I reproduced the generated Attach script skipping an existing sess 3.0.9000.9000 installation and then receiving Cannot attach R session: unsupported sess protocol version 1; this extension requires protocol version 2. The inline comment describes the fix.

Validation: TypeScript compilation, ESLint with no errors, production build/VSIX packaging, 42 viewer and integration tests, and 994 R assertions passed. These include the new Interactive nested-table session routing and pending table-request tests. A separate targeted upgrade reproduction confirmed the installation gap.

renkun-ken · 2026-10-04T23:43:25Z

  if (is.null(host) || is.na(host)) host <- ""
  list(
-    protocol_version = 1L,
+    protocol_version = 2L,


[P2] Make the protocol bump trigger a sess package update

The protocol changes to 2 while sess/DESCRIPTION remains 3.0.9000.9000, the same version as the protocol-1 package on the base revision. Both promptToInstallSessPackage and the generated Attach script compare only package versions, so an existing installation is considered current and never replaced. I reproduced the generated Attach script skipping the old installation, followed by the extension rejecting its handshake with unsupported sess protocol version 1; this extension requires protocol version 2. Bump the sess package version together with this protocol change, or check protocol compatibility in both installation paths, so existing users can attach after upgrading.

…names retain [index] labels.

- reuse data viewer formatting for list and vector values - route scalar value to the shared list viewer for consistency

Replace copied List Viewer control SVGs with @vscode/codicons. Bundle its CSS, font, and licenses. Move attribution from README into third-party notices covering Codicons, existing viewer tab icons, and the R logo.

renkun-ken

Reviewed revision 5fd29ce0c0d27a8f999e735284622ba2f36e8947. The previous upgrade finding is resolved: the package version is bumped to 3.0.9000.9001, and the rebased source-identity checks also detect an old installation. I reran the generated Attach command against the prior protocol-1 package in a temporary library; it installed the bundled copy and connected with protocol 2.

One packaging issue remains: .vscodeignore contains unresolved rebase conflicts. Both sides' inclusion rules are active, so the VSIX ships the raw, unstamped sess/ tree and R/tests/ in addition to the prepared package. The inline comment describes the required conflict resolution.

Validation: TypeScript compilation, ESLint with no errors, production build/VSIX packaging, packaged source-identity verification, 53 targeted viewer/integration/installation tests, and 994 R assertions passed. The separate upgrade reproduction passed as well. macOS CI remains red on the existing workspace-focus assertion; that test passed in the local targeted run, so I have not established a PR runtime regression from that failure.

renkun-ken · 2026-10-05T00:27:06Z

+!R/**
+!sess/**
+>>>>>>> 109dc25 (refactor(viewer): use packaged codicons and consolidate icon notices)


[P2] Resolve the rebase conflicts in the packaging allowlist

Both conflict blocks are still committed. vsce treats the markers as ordinary patterns and applies both sides, so !R/** and !sess/** undo the base's selective exclusions. I inspected the generated VSIX: it contains 47 raw sess/ files with the unexpanded source-revision placeholder, plus R/tests/sess_source.R, alongside the prepared dist/resources/sess/ package. Resolve both blocks by keeping the base's selective R paths and prepared sess inclusion, then add the notices, Codicons font, and license entries. I verified that this removes the 48 unintended files while retaining all required resources.

renkun-ken

Reviewed revision b470e57b6e4e3edc40e883b4035855c4ba84e050. The previous packaging finding is resolved: both conflict blocks are removed, the selective R inclusion rules are restored, and the prepared sess package, Codicons font/CSS, and license notices remain included. I inspected the generated VSIX and confirmed that the raw sess/ tree and R/tests/ are excluded, while the bundled sess DESCRIPTION has the correct source identity and bootstrap disabled.

This revision changes only .vscodeignore; the previously reviewed runtime code is unchanged. Local production build, VSIX packaging, packaged source-identity verification, and archive-content checks passed. All current CI checks are green, including build, lint, and macOS/Linux/Windows tests. No further actionable findings.

Requested protocol version update has been resolved.

Sorry, unreleased version yet, so version 1 is ok.

Fred-Wu added this to the 3.x milestone Sep 20, 2026

This was referenced Sep 20, 2026

Viewing List Objects in VSCODE #1399

Closed

View() on lists shows blank pane — jquery.json-viewer.css path mismatch in 2.8.7 #1687

Closed

View button for nested data.frames in Workspace Viewer #1576

Closed

randy3k changed the base branch from master to main September 26, 2026 16:57

Fred-Wu force-pushed the feature/list-viewer-1399 branch 3 times, most recently from 3973a3b to 5796fdf Compare October 3, 2026 10:00

renkun-ken requested changes Oct 4, 2026

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Fred-Wu force-pushed the feature/list-viewer-1399 branch 2 times, most recently from 07f39de to 997730c Compare October 4, 2026 12:56

Fred-Wu marked this pull request as ready for review October 4, 2026 13:27

Fred-Wu requested a review from renkun-ken October 4, 2026 13:27

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Fred-Wu requested a review from eitsupi October 4, 2026 15:09

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Fred-Wu force-pushed the feature/list-viewer-1399 branch from 43b78ca to 109dc25 Compare October 4, 2026 23:37

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Fred-Wu added 4 commits October 5, 2026 10:57

Enable viewing nested workspace lists and tables

5bdb1ba

Show shallow list summaries with child navigation

54c166d

Match list viewer actions to workspace View icons

0588cde

Reuse list viewer panels by title

dd26ffa

Fred-Wu added 13 commits October 5, 2026 10:57

fix(viewer): avoid evaluating active root bindings twice

65d61d1

fix(viewer): preserve custom extraction semantics

7582cc9

fix(viewer): preserve names for named vectors while empty or missing …

6647d3f

…names retain [index] labels.

fix(viewer):

89adf4f

- reuse data viewer formatting for list and vector values - route scalar value to the shared list viewer for consistency

fix(viewer): prevent stale disposal from deleting reopened viewer state

65ca487

fix(viewer): isolate reloaded viewer responses

1d66df6

fix(viewer): update runtime start test arguments

13997ce

fix(viewer): update viewer lifecycle test

9063765

fix(viewer): update document generation test

2afc534

fix(viewer): cover pending data viewer request

15066ab

Bumped sess IPC to version 2

b2d72f8

refactor(viewer): use packaged codicons and consolidate icon notices

be2dc6a

Replace copied List Viewer control SVGs with @vscode/codicons. Bundle its CSS, font, and licenses. Move attribution from README into third-party notices covering Codicons, existing viewer tab icons, and the R logo.

Update sess version number to 3.0.9000.9001 along with IPC change

5fd29ce

Fred-Wu force-pushed the feature/list-viewer-1399 branch from e8ddfb3 to 5fd29ce Compare October 4, 2026 23:59

Fred-Wu requested a review from renkun-ken October 5, 2026 00:00

renkun-ken requested changes Oct 5, 2026

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fix(build): resolve vscodeignore packaging conflict

b470e57

Fred-Wu requested a review from renkun-ken October 5, 2026 00:50

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eitsupi mentioned this pull request Oct 5, 2026

3.1.0 release #1824

Open

fix(session): resolve dataview rebase conflict

246cb7f

Fred-Wu force-pushed the feature/list-viewer-1399 branch from 6b044fe to 246cb7f Compare October 5, 2026 01:25

Merge branch 'main' into feature/list-viewer-1399

8c1f3b9

Fred-Wu added 2 commits October 5, 2026 12:57

fix(viewer): resolve lint regressions

3347be4

fix(viewer): update merged session tests

9e9c441

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Fred-Wu merged commit c8050e0 into REditorSupport:main Oct 5, 2026
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		label <- if (!is.null(view_id) && isTRUE(vector_view)) {
		paste0("[", index, "]")

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Fred-Wu commented Sep 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

List Viewer

Nested navigation

On-demand loading

Session-aware viewers

Viewer lifecycle fixes

Tests

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Fred-Wu commented Sep 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Fred-Wu commented Sep 20, 2026 •

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