[ViralBShah]

When f, or the conversion of its result to the destination's element type, throws part-way through an in-place map! or broadcast!, the sparse destination is left with a pattern that is half-written: column pointers of the new result next to those of the old one. The next use of it fails an internal assertion or reads the wrong entries.

Before (on #1071; the same on main and Julia 1.13)

julia> B = sparse([1.0 0 0 4; 0 2 0 0; 0 0 3 0; 1 1 0 0]);

julia> B .= ((x, y) -> x == 3 ? error("boom") : x + y).(B, sparse(ones(4, 4)))
ERROR: boom

julia> Array(B)
ERROR: AssertionError: _goodbuffers(S)

After

julia> B .= ((x, y) -> x == 3 ? error("boom") : x + y).(B, sparse(ones(4, 4)))
ERROR: boom

julia> Array(B)
4×4 Matrix{Float64}:
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

julia> nnz(B)
0

The kernels rebuild the pattern of the destination, or densify it, as they go, so a throw from f leaves it between two patterns. The dispatchers of map! and broadcast! now call the kernel inside a try (_guardpattern for the zero-preserving kernels, the existing _guardfill for those that fill, and the zero-argument C .= f.() path), and on a throw empty the destination before rethrowing. The kernels themselves are unchanged.

Behaviour to review: after a throw, a destination that is not fixed is in one of three states, never structurally invalid.

• Untouched when the failure can be found first: the index type cannot address every entry, or the fill value f(0) does not convert. That is Validate before densifying the destination of map! and broadcast! #1071.
• Partly written, as a dense destination is, for one argument whose pattern the destination already has (C .= f.(C)). This is what main does.
• Empty otherwise, since the pattern, or the filled values, are then no longer the destination's own. It is not restored.

A fixed destination keeps its pattern throughout, as before. Truncating at the failing column instead of emptying needs loop state in the catch, which costs the hot loop.

The try is outside the kernels. Minimum of 15 runs, time in ms and allocated bytes, n = 10^5 square with about 10^6 stored entries per argument (map!(cos, C, A): a 1000×1000 destination, all 10^6 entries stored):

	#1071	this PR
map(sin, A)	10.548, 16815672	10.458, 16815672
map(+, A, B)	15.268, 32839224	15.249, 32839224
A .* B	12.570, 32839320	12.599, 32839320
map!(+, C, A, B)	12.577, 48	12.800, 48
C .= A .+ B	12.563, 144	12.689, 144
map!(cos, C, A)	0.207, 48	0.211, 48

The out-of-place rows do not go through the new code. The inferred result types of all six are unchanged.

Split from #1022.

Backport: this fixes a corrupted destination, but it also changes what a destination holds after a throw (empty, where it used to be invalid but with some of its old entries readable), so it is a behaviour change as well as a fix.

Written by Claude Code.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.75%. Comparing base (c85e991) to head (674de31).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/higherorderfns.jl	95.45%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1082      +/-   ##
==========================================
- Coverage   94.77%   94.75%   -0.02%     
==========================================
  Files          16       16              
  Lines        9917     9958      +41     
==========================================
+ Hits         9399     9436      +37     
- Misses        518      522       +4     

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[ViralBShah]

Reviewed by Codex at bd3ad1c.

No actionable findings. The guards surround the pattern-building kernels, preserve the same-pattern unary case, and clear partial mutable structure after other failures; fixed destinations retain their existing path. The preflight fill conversion remains outside the mutation region.