Version: 1.59.0 (user setup)
Commit: 379476f
Date: 2021-08-04T23:13:12.822Z
Electron: 13.1.7
Chrome: 91.0.4472.124
Node.js: 14.16.0
V8: 9.1.269.36-electron.0
OS: Windows_NT x64 10.0.19043

This was originally reported against the C/C++ extension here: microsoft/vscode-cpptools#7826

There appears to be some truncation that occurs in the Refactor Preview panel. Repro is fairly simple, but involves using the C/C++ Extension. Note that the C/C++ Extension does not return the contents of the line replicated in the Refactor Preview panel. It only provides the range to be replaced, what to replace it with, what Icon to use, text for the group label, etc.. The remainder of the line extracted from the original file appears to be coming from VS Code.

Repro code:

int foo(void)
{
    int foo = 1; // A much longer line that is not trunacated.
}

int main(void)
{
    foo();
}

The repro is to use the Rename feature to change foo to foo2.