PersistedWindowFrame — Specs

Summary

NSWindow.isValidPersistedFrame(_:) (defined in HelperExtensionsTestable.swift) decides whether a window-frame string that AppKit persisted in UserDefaults (key "NSWindow Frame <name>") is safe to restore. AppKit's setFrameAutosaveName / setFrameUsingName immediately apply that string, and an out-of-range or non-finite frame makes the apply throw NSInternalInconsistencyException and abort the app (crash f481d5b0, FeedbackWindow). setFrameAutosaveNameSafely calls this predicate and drops a corrupt value before AppKit ever sees it.

The persisted string is space-separated numbers: the window frame x y w h, optionally followed by the save-time screen frame x y w h (so 4 or 8 tokens), with a trailing space. AppKit's own validity rule is CGRectContainsRect(CGRectMake(INT_MIN, INT_MIN, INT_MAX-INT_MIN, INT_MAX-INT_MIN), frame) — i.e. every edge must stay within Int32 bounds and be finite. This predicate mirrors that rule exactly.

Behavior & edge cases

• At least 4 numeric tokens are required (the window frame). Fewer → invalid.
• Parsing is C-locale via Double(Substring) (period decimal, never comma); "nan"/"inf" parse to non-finite values and are rejected by the isFinite check.
• Every token must be finite and within Int32 bounds (Int32.min ... Int32.max) — this is the exact range AppKit's CGRectContainsRect enforces; values outside it are what abort the app.
• Width and height must be non-negative, and x + w / y + h must not overflow Int32.max (a frame whose origin is in range but whose far edge isn't is still rejected).
• Negative origins are valid (windows legitimately sit at negative coordinates on a secondary display placed left of / below the main one).
• Non-numeric junk tokens are dropped before counting (compactMap), so an all-garbage string yields zero tokens → invalid.

Test scenarios

Mirrors PersistedWindowFrameTests.swift 1:1.

A. Valid frames

• testLiveEightTokenStringWithTrailingSpaceIsValid — the real on-disk format ("834 503 380 450 0 0 2048 1121 ") is accepted, trailing space and all.
• testFourTokenWindowOnlyFrameIsValid — a bare x y w h (no screen tokens) is accepted.
• testNegativeOriginIsValid — a frame at negative coordinates (secondary-display placement) is accepted.
• testInt32MaxBoundaryIsValid — a frame whose far edge lands exactly on Int32.max is accepted.

B. Non-finite / out-of-range (the crash cases)

• testNaNTokenIsInvalid — a nan token is rejected.
• testInfiniteTokenIsInvalid — an inf token is rejected.
• testValueBeyondInt32IsInvalid — a coordinate larger than Int32.max is rejected.
• testFarEdgeOverflowIsInvalid — an in-range origin with a width that pushes x + w past Int32.max is rejected.

C. Malformed strings

• testNegativeWidthOrHeightIsInvalid — negative w/h is rejected.
• testFewerThanFourTokensIsInvalid — three tokens is rejected.
• testAllJunkTokensIsInvalid — non-numeric tokens yield zero numbers and are rejected.
• testEmptyStringIsInvalid — the empty string is rejected.