[lldb] add a marker before skipped frames #167550

charles-zablit · 2025-11-11T17:29:10Z

This patch adds a marker to make skipped frames more explicit.

Skipped frames can be confusing for some users, who see that the indexes of the frames in a backtrace are not contiguous. This patch aims to lessen the confusion by adding a delimiter for the first and last non skipped frame, i.e the boundaries.

IDE's like Xcode and VSCode represent those in the UI by having the skipped frames either greyed out or collapsed.

It's not possible to do this in the CLI, therefore, this patch makes use of 2 unicode characters to mark the beginning and end of the skipped frames range.

This patch depends on:

[lldb] improve the heuristics for checking if a terminal supports Unicode #168603

Examples

In the example below, frame #2 to #7 are is skipped, and therefore, frame #1 is the first non skipped frame of the range while frame #8 is the last non skipped frame:

If the selected frame is one of the 2 boundary frames, we replace the delimiter character with the select character (*).

llvmbot · 2025-11-11T17:29:44Z

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

Changes

This patch adds a marker to make skipped frames more explicit.

Skipped frames can be confusing for some users, who see that the indexes of the frames in a backtrace are not contiguous. This patch aims to lessen the confusion by adding a delimiter for the first and last non skipped frame, i.e the boundaries.

IDE's like Xcode and VSCode represent those in the UI by having the skipped frames either greyed out or collapsed.

It's not possible to do this in the CLI, therefore, this patch makes use of 2 unicode characters to mark the beginning and end of the skipped frames range.

In the example below, frame #2 is skipped, and therefore, frame #1 is the first skipped frame of the range while frame #3 is the last non skipped frame:
<img width="553" height="132" alt="Screenshot 2025-11-11 at 18 27 41" src="https://github.com/user-attachments/assets/7d573b1f-80fb-456b-86d8-dfeedf479375" />

Full diff: https://github.com/llvm/llvm-project/pull/167550.diff

4 Files Affected:

(modified) lldb/include/lldb/Target/StackFrame.h (+18-3)
(modified) lldb/include/lldb/Target/StackFrameList.h (+8)
(modified) lldb/source/Target/StackFrame.cpp (+16-6)
(modified) lldb/source/Target/StackFrameList.cpp (+24-2)

diff --git a/lldb/include/lldb/Target/StackFrame.h b/lldb/include/lldb/Target/StackFrame.h
index cdbe8ae3c6779..c3e3c945e114c 100644
--- a/lldb/include/lldb/Target/StackFrame.h
+++ b/lldb/include/lldb/Target/StackFrame.h
@@ -335,11 +335,16 @@ class StackFrame : public ExecutionContextScope,
   /// \param[in] frame_marker
   ///   Optional string that will be prepended to the frame output description.
   ///
+  /// \param[in] skipped_frame_marker
+  ///   Optional string that will be prepended to the first or last non skipped
+  ///   frame output description.
+  ///
   /// \return
   ///   \b true if and only if dumping with the given \p format worked.
   bool DumpUsingFormat(Stream &strm,
                        const lldb_private::FormatEntity::Entry *format,
-                       llvm::StringRef frame_marker = {});
+                       llvm::StringRef frame_marker = {},
+                       llvm::StringRef skipped_frame_marker = {});
 
   /// Print a description for this frame using the frame-format formatter
   /// settings. If the current frame-format settings are invalid, then the
@@ -353,8 +358,13 @@ class StackFrame : public ExecutionContextScope,
   ///
   /// \param [in] frame_marker
   ///   Optional string that will be prepended to the frame output description.
+  ///
+  /// \param[in] skipped_frame_marker
+  ///   Optional string that will be prepended to the first or last non skipped
+  ///   frame output description.
   void DumpUsingSettingsFormat(Stream *strm, bool show_unique = false,
-                               const char *frame_marker = nullptr);
+                               const char *frame_marker = nullptr,
+                               const std::wstring skipped_frame_marker = L"");
 
   /// Print a description for this frame using a default format.
   ///
@@ -387,10 +397,15 @@ class StackFrame : public ExecutionContextScope,
   /// \param[in] frame_marker
   ///   Passed to DumpUsingSettingsFormat() for the frame info printing.
   ///
+  ///
+  /// \param[in] skipped_frame_marker
+  ///   Optional string that will be prepended to the first or last non skipped
+  ///   frame output description.
   /// \return
   ///   Returns true if successful.
   bool GetStatus(Stream &strm, bool show_frame_info, bool show_source,
-                 bool show_unique = false, const char *frame_marker = nullptr);
+                 bool show_unique = false, const char *frame_marker = nullptr,
+                 const std::wstring skipped_frame_marker = L"");
 
   /// Query whether this frame is a concrete frame on the call stack, or if it
   /// is an inlined frame derived from the debug information and presented by
diff --git a/lldb/include/lldb/Target/StackFrameList.h b/lldb/include/lldb/Target/StackFrameList.h
index ea9aab86b8ea1..122c256bd61d3 100644
--- a/lldb/include/lldb/Target/StackFrameList.h
+++ b/lldb/include/lldb/Target/StackFrameList.h
@@ -49,6 +49,14 @@ class StackFrameList {
   /// Resets the selected frame index of this object.
   void ClearSelectedFrameIndex();
 
+  /// Return \code true if the next frame is hidden. False otherwise or if it's
+  /// the last frame.
+  bool IsNextFrameHidden(lldb_private::StackFrame &frame);
+
+  /// Return \code true if the previous frame is hidden. False otherwise or if
+  /// it's the first frame.
+  bool IsPreviousFrameHidden(lldb_private::StackFrame &frame);
+
   /// Get the currently selected frame index.
   /// We should only call SelectMostRelevantFrame if (a) the user hasn't already
   /// selected a frame, and (b) if this really is a user facing
diff --git a/lldb/source/Target/StackFrame.cpp b/lldb/source/Target/StackFrame.cpp
index 2ed58c5331df4..03c595cd49656 100644
--- a/lldb/source/Target/StackFrame.cpp
+++ b/lldb/source/Target/StackFrame.cpp
@@ -37,6 +37,7 @@
 #include "lldb/ValueObject/ValueObjectConstResult.h"
 #include "lldb/ValueObject/ValueObjectMemory.h"
 #include "lldb/ValueObject/ValueObjectVariable.h"
+#include "llvm/Support/ConvertUTF.h"
 
 #include "lldb/lldb-enumerations.h"
 
@@ -1920,11 +1921,13 @@ void StackFrame::CalculateExecutionContext(ExecutionContext &exe_ctx) {
 
 bool StackFrame::DumpUsingFormat(Stream &strm,
                                  const FormatEntity::Entry *format,
-                                 llvm::StringRef frame_marker) {
+                                 llvm::StringRef frame_marker,
+                                 llvm::StringRef skipped_frame_marker) {
   GetSymbolContext(eSymbolContextEverything);
   ExecutionContext exe_ctx(shared_from_this());
   StreamString s;
   s.PutCString(frame_marker);
+  s.PutCString(skipped_frame_marker);
 
   if (format && FormatEntity::Format(*format, s, &m_sc, &exe_ctx, nullptr,
                                      nullptr, false, false)) {
@@ -1934,8 +1937,9 @@ bool StackFrame::DumpUsingFormat(Stream &strm,
   return false;
 }
 
-void StackFrame::DumpUsingSettingsFormat(Stream *strm, bool show_unique,
-                                         const char *frame_marker) {
+void StackFrame::DumpUsingSettingsFormat(
+    Stream *strm, bool show_unique, const char *frame_marker,
+    const std::wstring skipped_frame_marker) {
   if (strm == nullptr)
     return;
 
@@ -1953,7 +1957,11 @@ void StackFrame::DumpUsingSettingsFormat(Stream *strm, bool show_unique,
       frame_format = &format_entry;
     }
   }
-  if (!DumpUsingFormat(*strm, frame_format, frame_marker)) {
+
+  std::string skipped_frame_delimiter_utf8;
+  llvm::convertWideToUTF8(skipped_frame_marker, skipped_frame_delimiter_utf8);
+  if (!DumpUsingFormat(*strm, frame_format, frame_marker,
+                       skipped_frame_delimiter_utf8)) {
     Dump(strm, true, false);
     strm->EOL();
   }
@@ -2034,10 +2042,12 @@ bool StackFrame::HasCachedData() const {
 }
 
 bool StackFrame::GetStatus(Stream &strm, bool show_frame_info, bool show_source,
-                           bool show_unique, const char *frame_marker) {
+                           bool show_unique, const char *frame_marker,
+                           const std::wstring skipped_frame_marker) {
   if (show_frame_info) {
     strm.Indent();
-    DumpUsingSettingsFormat(&strm, show_unique, frame_marker);
+    DumpUsingSettingsFormat(&strm, show_unique, frame_marker,
+                            skipped_frame_marker);
   }
 
   if (show_source) {
diff --git a/lldb/source/Target/StackFrameList.cpp b/lldb/source/Target/StackFrameList.cpp
index ccf874fc03ebd..80f77e2bcee16 100644
--- a/lldb/source/Target/StackFrameList.cpp
+++ b/lldb/source/Target/StackFrameList.cpp
@@ -879,6 +879,24 @@ StackFrameList::GetStackFrameSPForStackFramePtr(StackFrame *stack_frame_ptr) {
   return ret_sp;
 }
 
+bool StackFrameList::IsNextFrameHidden(lldb_private::StackFrame &frame) {
+  uint32_t frame_idx = frame.GetFrameIndex();
+  StackFrameSP frame_sp = GetFrameAtIndex(frame_idx + 1);
+  if (!frame_sp)
+    return false;
+  return frame_sp->IsHidden();
+}
+
+bool StackFrameList::IsPreviousFrameHidden(lldb_private::StackFrame &frame) {
+  uint32_t frame_idx = frame.GetFrameIndex();
+  if (frame_idx == 0)
+    return false;
+  StackFrameSP frame_sp = GetFrameAtIndex(frame_idx - 1);
+  if (!frame_sp)
+    return false;
+  return frame_sp->IsHidden();
+}
+
 size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
                                  uint32_t num_frames, bool show_frame_info,
                                  uint32_t num_frames_with_source,
@@ -920,6 +938,11 @@ size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
       else
         marker = unselected_marker;
     }
+    std::wstring skipped_frame_marker = L"　";
+    if (IsPreviousFrameHidden(*frame_sp))
+      skipped_frame_marker = L"﹈";
+    else if (IsNextFrameHidden(*frame_sp))
+      skipped_frame_marker = L"﹇";
 
     // Hide uninteresting frames unless it's the selected frame.
     if (!show_hidden && frame_sp != selected_frame_sp && frame_sp->IsHidden())
@@ -933,10 +956,9 @@ size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
             m_thread.GetID(), num_frames_displayed))
       break;
 
-
     if (!frame_sp->GetStatus(strm, show_frame_info,
                              num_frames_with_source > (first_frame - frame_idx),
-                             show_unique, marker))
+                             show_unique, marker, skipped_frame_marker))
       break;
     ++num_frames_displayed;
   }

charles-zablit · 2025-11-11T17:30:21Z

I think this patch still has room for improvements (I should also add some tests). I'm curious about the thoughts people might have about those brackets?

jimingham · 2025-11-11T17:34:53Z

Brackets for indicating elided stuff has precedent in other areas, so that seems pretty clear to me. It's enough to tell you "this is intentional" without being too eye-catching. Seems good to me.

charles-zablit · 2025-11-11T18:09:56Z

Brackets for indicating elided stuff has precedent in other areas, so that seems pretty clear to me. It's enough to tell you "this is intentional" without being too eye-catching. Seems good to me.

Thanks! I will try to reformat this a bit so that we don't have this wide space between the * and the frame.

JDevlieghere · 2025-11-11T18:21:16Z

I'm fine with the brackets. Another alternative could be https://www.compart.com/en/unicode/U+FE4D but maybe that ends up being too subtle?

charles-zablit · 2025-11-11T18:32:00Z

﹍
﹉

Could work, I will post a new screenshot 👍

Michael137 · 2025-11-12T10:33:57Z

lldb/include/lldb/Target/StackFrameList.h

+  /// Return \code true if the next frame is hidden. False otherwise or if it's
+  /// the last frame.


Suggested change

/// Return \code true if the next frame is hidden. False otherwise or if it's

/// the last frame.

/// Return \code true if the next frame is hidden.

I'd say it's implied that if we're at the first/last frame, then querying anything about the previous/next frame is not going to be valid. Not sure we need to document that

Fixed, thanks!

Michael137 · 2025-11-12T10:34:22Z

lldb/source/Target/StackFrame.cpp

-                                         const char *frame_marker) {
+void StackFrame::DumpUsingSettingsFormat(
+    Stream *strm, bool show_unique, const char *frame_marker,
+    const std::wstring skipped_frame_marker) {


Suggested change

const std::wstring skipped_frame_marker) {

const std::wstring &skipped_frame_marker) {

Fixed, thanks!

Michael137 · 2025-11-12T10:34:39Z

lldb/source/Target/StackFrame.cpp

@@ -2034,10 +2042,12 @@ bool StackFrame::HasCachedData() const {
 }

 bool StackFrame::GetStatus(Stream &strm, bool show_frame_info, bool show_source,
-                           bool show_unique, const char *frame_marker) {
+                           bool show_unique, const char *frame_marker,
+                           const std::wstring skipped_frame_marker) {


Suggested change

const std::wstring skipped_frame_marker) {

const std::wstring &skipped_frame_marker) {

Fixed, thanks!

Michael137 · 2025-11-12T11:01:02Z

lldb/source/Target/StackFrameList.cpp

@@ -920,6 +938,11 @@ size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
      else
        marker = unselected_marker;
    }
+    std::wstring skipped_frame_marker = L"　";


Remind me why we need wstring for this? Could this just be a utf-8 std::string from the beginning?

No special reason, I pushed the conversion further up the stack in 2c67401.

charles-zablit · 2025-11-18T18:48:17Z

I have updated the description of the PR to show the new appearance.

github-actions · 2025-11-18T18:55:10Z

🐧 Linux x64 Test Results

33166 tests passed
490 tests skipped

…code

adrian-prantl

LGTM with one minor comment inside

adrian-prantl · 2025-11-19T17:44:30Z

lldb/source/Utility/DiagnosticsRendering.cpp

  // Host so it can be customized for a specific platform.
  llvm::StringRef cursor, underline, vbar, joint, hbar, spacer;
-  if (stream.AsRawOstream().colors_enabled()) {
+  if (TerminalSupportsUnicode()) {


Thanks, this is long overdue!

adrian-prantl · 2025-11-19T17:45:44Z

lldb/source/Target/StackFrame.cpp


 void StackFrame::DumpUsingSettingsFormat(Stream *strm, bool show_unique,
-                                         const char *frame_marker) {
+                                         const std::string &frame_marker) {


We're passing this into a function that takes a StringRef — why not make it a StringRef, too?

adrian-prantl · 2025-11-19T17:46:40Z

lldb/include/lldb/Utility/DiagnosticsRendering.h

+/// The value is cached after the first computation.
+///
+/// On POSIX systems, we check if the LANG environment variable contains the
+/// substring "UTF-8";


That's so much better than checking for color!

JDevlieghere · 2025-11-19T23:59:06Z

lldb/include/lldb/Target/StackFrame.h

  ///   Optional string that will be prepended to the frame output description.
  void DumpUsingSettingsFormat(Stream *strm, bool show_unique = false,
-                               const char *frame_marker = nullptr);
+                               const std::string &frame_marker = "");


JDevlieghere · 2025-11-19T23:59:27Z

lldb/include/lldb/Utility/DiagnosticsRendering.h

+///
+/// On Windows, we check that we are running from the Windows Terminal
+/// application.
+bool TerminalSupportsUnicode();


Should we move this into Host/Terminal.h?

JDevlieghere · 2025-11-20T00:00:55Z

lldb/source/Utility/DiagnosticsRendering.cpp

+bool TerminalSupportsUnicode() {
+  static std::optional<bool> result;
+  if (result)
+    return result.value();
+#ifndef _WIN32
+  if (const char *lang_var = std::getenv("LANG"))
+    result = std::string(lang_var).find("UTF-8");
+  else
+    result = false;
+#else
+  result = std::getenv("WT_SESSION") != nullptr;
+#endif
+  return result.value();
+}


Will this be correct for Xcode and DAP?

JDevlieghere · 2025-11-20T00:01:03Z

lldb/source/Utility/DiagnosticsRendering.cpp

+    return result.value();
+#ifndef _WIN32
+  if (const char *lang_var = std::getenv("LANG"))
+    result = std::string(lang_var).find("UTF-8");


Suggested change

result = std::string(lang_var).find("UTF-8");

result = llvm::StringRef(lang_var).find("UTF-8");

JDevlieghere · 2025-11-20T00:01:17Z

lldb/source/Target/StackFrameList.cpp

+  if (frame_sp == selected_frame_sp) {
+    return TerminalSupportsUnicode() ? L" * " : L"* ";
+  } else if (!TerminalSupportsUnicode()) {
+    return L"  ";
+  } else if (IsPreviousFrameHidden(*frame_sp)) {
+    return L" ﹉";
+  } else if (IsNextFrameHidden(*frame_sp)) {
+    return L" ﹍";
+  }


JDevlieghere · 2025-11-20T00:06:09Z

Sorry, all my comments should have gone in the other PR :(

charles-zablit requested a review from JDevlieghere as a code owner November 11, 2025 17:29

llvmbot added the lldb label Nov 11, 2025

Michael137 reviewed Nov 12, 2025

View reviewed changes

charles-zablit added 5 commits November 18, 2025 20:47

[lldb] add a marker before skipped frames

533989a

align all markers

73548e6

remove unused comments

1ba6ded

make APIs use std::string instead of std::wstring

2bd30fd

[lldb] improve the heuristics for checking if a terminal supports Uni…

78385d4

…code

charles-zablit force-pushed the charles-zablit/lldb/mark-skipped-frames branch from 2c67401 to 78385d4 Compare November 18, 2025 19:48

charles-zablit requested review from Michael137 and adrian-prantl November 19, 2025 14:04

charles-zablit self-assigned this Nov 19, 2025

adrian-prantl reviewed Nov 19, 2025

View reviewed changes

JDevlieghere reviewed Nov 20, 2025

View reviewed changes

		/// Return \code true if the next frame is hidden. False otherwise or if it's
		/// the last frame.

	const std::wstring skipped_frame_marker) {
	const std::wstring &skipped_frame_marker) {

	result = std::string(lang_var).find("UTF-8");
	result = llvm::StringRef(lang_var).find("UTF-8");

[lldb] add a marker before skipped frames #167550

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🐧 Linux x64 Test Results

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charles-zablit commented Nov 11, 2025 •

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