https://github.com/Michael137 created
https://github.com/llvm/llvm-project/pull/149088
When dumping variables, LLDB will print a one-time warning about truncating
children (when the children count exceeds the default
`target.max-children-count`). But we only do this for `frame variable`. So if
we use `dwim-print` or `expression`, the output gets truncated but we don't
print a warning. But because we store the fact that we truncated some output on
the `CommandInterpreter`, we fire the warning next time we use `frame
variable`. E.g.,:
```
(lldb) p arr
(int[1000]) {
[0] = -5
[1] = 0
[2] = 0
<-- snipped -->
[253] = 0
[254] = 0
[255] = 0
...
}
(lldb) v someLocal
(int) someLocal = 10
*** Some of the displayed variables have more members than the debugger
will show by default. To show all of them, you can either use the
--show-all-children option to frame variable or raise the limit by
changing the target.max-children-count setting.
```
This patch prints the warning for `dwim-print` and `expression`.
I only added a test for the `target.max-children-count` for now because it
seems the `target.max-children-depth` warning is broken (I can't get it to
fire).
>From 659629fee5da453166ad38265e40ce1f297531f5 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuc...@gmail.com>
Date: Wed, 16 Jul 2025 10:29:28 +0100
Subject: [PATCH] [lldb] Print child-depth warning for DWIM-print and expr
When dumping variables, LLDB will print a one-time warning about
truncating children (when the children count exceeds the default
`target.max-children-count`). But we only do this for `frame variable`.
So if we use `dwim-print` or `expression`, the output gets truncated but
we don't print a warning. But because we store the fact that we
truncated some output on the `CommandInterpreter`, we fire the warning
next time we use `frame variable`. E.g.,:
```
(lldb) p arr
(int[1000]) {
[0] = -5
[1] = 0
[2] = 0
<-- snipped -->
[253] = 0
[254] = 0
[255] = 0
...
}
(lldb) v someLocal
(int) someLocal = 10
*** Some of the displayed variables have more members than the debugger
will show by default. To show all of them, you can either use the
--show-all-children option to frame variable or raise the limit by
changing the target.max-children-count setting.
```
This patch prints the warning for `dwim-print` and `expression`.
I only added a test for the `target.max-children-count` for now because
it seems the `target.max-children-depth` warning is broken (I can't get
it to fire).
---
.../Commands/CommandObjectDWIMPrint.cpp | 2 +
.../Commands/CommandObjectExpression.cpp | 3 +
.../Settings/TestChildCountTruncation.test | 67 +++++++++++++++++++
3 files changed, 72 insertions(+)
create mode 100644 lldb/test/Shell/Settings/TestChildCountTruncation.test
diff --git a/lldb/source/Commands/CommandObjectDWIMPrint.cpp
b/lldb/source/Commands/CommandObjectDWIMPrint.cpp
index a110eececf4d6..a2c004d0ee97f 100644
--- a/lldb/source/Commands/CommandObjectDWIMPrint.cpp
+++ b/lldb/source/Commands/CommandObjectDWIMPrint.cpp
@@ -150,6 +150,8 @@ void CommandObjectDWIMPrint::DoExecute(StringRef command,
return;
}
}
+ m_interpreter.PrintWarningsIfNecessary(result.GetOutputStream(),
+ m_cmd_name);
result.SetStatus(eReturnStatusSuccessFinishResult);
};
diff --git a/lldb/source/Commands/CommandObjectExpression.cpp
b/lldb/source/Commands/CommandObjectExpression.cpp
index a95dea63720ac..c5b91678103d5 100644
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -470,6 +470,9 @@ bool
CommandObjectExpression::EvaluateExpression(llvm::StringRef expr,
return false;
}
+ m_interpreter.PrintWarningsIfNecessary(result.GetOutputStream(),
+ m_cmd_name);
+
if (suppress_result)
if (auto result_var_sp =
target.GetPersistentVariable(result_valobj_sp->GetName())) {
diff --git a/lldb/test/Shell/Settings/TestChildCountTruncation.test
b/lldb/test/Shell/Settings/TestChildCountTruncation.test
new file mode 100644
index 0000000000000..3b75498297b05
--- /dev/null
+++ b/lldb/test/Shell/Settings/TestChildCountTruncation.test
@@ -0,0 +1,67 @@
+# Test that we warn the user about truncated output
+# when target.max-children-count wasn't explicitly set.
+
+# RUN: split-file %s %t
+# RUN: %clang_host -g -gdwarf %t/main.cpp -o %t.out
+# RUN: %lldb -x -b -s %t/dwim-commands.input %t.out -o exit 2>&1 \
+# RUN: | FileCheck %s --check-prefix=DWIM
+#
+# RUN: %lldb -x -b -s %t/expr-commands.input %t.out -o exit 2>&1 \
+# RUN: | FileCheck %s --check-prefix=EXPR
+#
+# RUN: %lldb -x -b -s %t/frame-var-commands.input %t.out -o exit 2>&1 \
+# RUN: | FileCheck %s --check-prefix=VAR
+#
+# RUN: %lldb -x -b -s %t/with-setting-commands.input %t.out -o exit 2>&1 \
+# RUN: | FileCheck %s --check-prefix=SETTING
+
+#--- main.cpp
+
+int main() {
+ int arr[512] = { 3 };
+ __builtin_debugtrap();
+}
+
+#--- dwim-commands.input
+
+run
+dwim-print arr
+frame variable arr
+
+DWIM: (lldb) dwim-print arr
+DWIM: *** Some of the displayed variables have more members
+DWIM-SAME: use the --show-all-children option to dwim-print
+DWIM: (lldb) frame variable arr
+DWIM-NOT: *** Some of the displayed variables have more members
+
+#--- expr-commands.input
+
+run
+expression arr
+frame variable arr
+
+EXPR: (lldb) expression arr
+EXPR: *** Some of the displayed variables have more members
+EXPR-SAME: use the --show-all-children option to expression
+EXPR: (lldb) frame variable arr
+EXPR-NOT: *** Some of the displayed variables have more members
+
+#--- frame-var-commands.input
+
+run
+frame variable arr
+
+VAR: (lldb) frame variable arr
+VAR: *** Some of the displayed variables have more members
+VAR-SAME: use the --show-all-children option to frame variable
+VAR: (lldb) frame variable arr
+VAR-NOT: *** Some of the displayed variables have more members
+
+#--- with-setting-commands.input
+
+run
+settings set target.max-children-count 1
+frame variable arr
+
+SETTING: (lldb) frame variable arr
+SETTING-NOT: *** Some of the displayed variables have more members
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