Recalculate window size after a screen buffer resize - #20647
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SetConsoleScreenBufferSize/SetConsoleScreenBufferInfoEx only called UpdateScrollBars() after resizing the buffer, which hides or shows the scroll bar control but doesn't touch the window's outer pixel rect. Window::s_CalculateWindowRect reserves extra space for a scroll bar based on comparing the window's character size against the buffer's - if that comparison was true at some earlier point (e.g. mid-resize, while the buffer was still its old, larger size) but becomes false once the buffer catches up, the previously-reserved margin is never reclaimed, leaving a stretch of unpainted background where a scroll bar used to be needed. This is most visible with the classic safe console-resize sequence (shrink the window, resize the buffer, grow the window back if needed): if growing the window back isn't necessary because the target size doesn't exceed the window's original size, the sequence ends right after the buffer resize with no further window-size call to clean up the stale reservation. Fix: ResizeScreenBuffer also posts a window-size recalculation alongside the existing scroll bar update, so the window rect is always re-evaluated against the buffer's current (not previous) size. Gated on the same fDoScrollBarUpdate flag the scroll bar update itself already uses - callers that pass false already trigger their own window resize immediately afterward.
A small standalone console tool (src/tools/resizewindowtest) that performs the shrink-window / resize-buffer / grow-window-if-needed sequence described in the previous commit, then fills the buffer with a solid color so a reviewer can see at a glance whether stale scroll-bar-reserved space is left behind at the window's right/bottom edge - even when GetConsoleScreenBufferInfo reports the buffer and window character dimensions matching exactly. Usage: resizewindowtest.exe [width height] (defaults to 80x25, which reliably reproduces the bug without this fix - the "grow window back" step of the sequence is skipped for any target height at or below the console's default window height).
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check-spelling flagged resizewindowtest as an unrecognized word - both in the new tool's source and, per docs.check-spelling.dev's check-file-path check, in the paths of the three files added under src/tools/resizewindowtest/.
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Summary of the Pull Request
Fixes a stale-window-space bug: after SetConsoleScreenBufferSize/SetConsoleScreenBufferInfoEx resizes the screen buffer, the
console window's outer pixel size was never re-evaluated against the new buffer dimensions. If the window had previously
reserved extra pixel space for a scroll bar (based on the buffer size at that time), and the buffer later shrinks so the scroll
bar is no longer needed, that reserved space is never reclaimed — leaving a permanent strip of unpainted background between the
actual content and the window's edge.
References and Relevant Issues
No existing tracked issue. Found while validating an unrelated console-buffer resize sequence that happened to exercise this
path.
Detailed Description of the Pull Request / Additional comments
Window::s_CalculateWindowRect (src/interactivity/win32/window.cpp) compares the window's character size against the buffer's
character size to decide whether to reserve extra pixel space for a scroll bar. SCREEN_INFORMATION::ResizeScreenBuffer
(src/host/screenInfo.cpp) calls UpdateScrollBars() after resizing the buffer, but that only shows/hides the scroll bar control —
it doesn't touch the window's outer rect. So if the reservation was computed against a stale, larger buffer size, it's only
cleaned up if a subsequent SetConsoleWindowInfo call happens to run afterward and re-triggers the rect calculation.
This is easy to hit with the standard safe console-resize sequence recommended for shrinking or growing a console (shrink window
→ resize buffer → grow window back only if the target exceeds the window's pre-resize size): whenever the final "grow" step is
skipped because it isn't needed, the sequence ends right after the buffer resize with the stale reservation never cleaned up.
Fix: ResizeScreenBuffer now also calls PostUpdateWindowSize() right after UpdateScrollBars(), gated on the same
fDoScrollBarUpdate flag the existing scroll bar update already uses — callers that pass false already trigger their own window
resize immediately afterward, so this avoids posting it twice there.
Validation Steps Performed
A reproduction tool is included in this PR (src/tools/resizewindowtest). It performs the shrink-window / resize-buffer /
grow-window-if-needed sequence described above, then fills the whole buffer with a solid color.
To reproduce:
resizewindowtest.exe (defaults to 80x25)
GetConsoleScreenBufferInfo reports the buffer and window character dimensions as identical.
change) to confirm no regression there.
PR Checklist