Core tests broken on master: src/qr.jl calls removed `SparseColumnPivotedQR.csr_qr` (renamed to `scpqr` in v2.x)

Summary

GROUP=Core (and therefore GROUP=All) fails on a clean, unmodified main checkout. This is not a flake and is not caused by any test-structure change — it reproduces on pristine main.

ERROR: LoadError: Some tests did not pass: 480 passed, 11 failed, 37 errored, 0 broken.

(Re-runs show a 1–2 test wobble — e.g. 12 failed / 36 errored — because several failing cases use randomized matrices without a fixed seed; the failure set is otherwise stable.)

Root cause (dominant: 19 errors)

src/qr.jl calls SparseColumnPivotedQR.csr_qr:

src/qr.jl:65:    Qaug = SparseColumnPivotedQR.csr_qr(_bordered_csr(MaugC))
src/qr.jl:108:    F.QaugH === nothing && (F.QaugH = SparseColumnPivotedQR.csr_qr(_adjoint_csr(F.MaugC)))
src/qr.jl:114:_augfact_tr!(F::SparseWithDenseRowColQRAugmented) = SparseColumnPivotedQR.csr_qr(_transpose_csr(F.MaugC))

But SparseColumnPivotedQR v2.1.1 (which resolves under this package's SparseColumnPivotedQR = "0.1, 2.1" compat) no longer defines csr_qr — the API was renamed. Its current public surface is:

names(SparseColumnPivotedQR):
  SparseColumnPivotedQRFactorization
  SparseColumnPivotedQRSymbolic
  has_amd_extension
  scpqr
  scpqr_analyze
  scpqr_factor
  scpqr_refactor!
isdefined(SparseColumnPivotedQR, :csr_qr) == false

So every QR-path test errors:

well-conditioned: qr agrees with factorize at the noise floor: Error During Test at test/test_qr.jl:31
  Got exception outside of a @test
  UndefVarError: `csr_qr` not defined in `SparseColumnPivotedQR`

This accounts for all 19 UndefVarError errors (test_qr.jl and the QR-routed cases in test_linearsolve.jl / test_edgecases.jl).

Secondary cause (augmented singular path)

A handful of test/test_augmented.jl cases throw BoundsError where LinearAlgebra.SingularException is expected:

:auto falls back to augmented when S is singular: Test Failed at test/test_augmented.jl:30
  Expression: factorize(A; strategy = :woodbury, auto_fallback = false)
    Expected: LinearAlgebra.SingularException
      Thrown: BoundsError
      BoundsError: attempt to access 50×2 Matrix{Float64} at index [0, 1]

i.e. the singular-S detection in the Woodbury/augmented path indexes a zero-length pivot vector at [0, 1] instead of surfacing SingularException.

Reproduction

git clone https://github.com/SciML/SparseWithDenseRowColMatrices.jl
cd SparseWithDenseRowColMatrices.jl
GROUP=Core julia +1.11 --project=. -e 'using Pkg; Pkg.instantiate(); Pkg.test()'

Reproduced on Julia 1.11.9, SparseColumnPivotedQR v2.1.1.

Suggested fix (separate PR)

Rename the three SparseColumnPivotedQR.csr_qr(...) call sites in src/qr.jl to the current API (scpqr / scpqr_analyze + scpqr_factor), confirming the new call returns the same factorization object the QR path expects. Separately, investigate the [0, 1] indexing in the augmented singular-detection path so it raises SingularException as the tests assert. Both are src/ bugs and should not be addressed by loosening or skipping the tests.

🤖 Generated with Claude Code

Start by reproducing GROUP=Core with the provided Julia command, then inspect the three SparseColumnPivotedQR calls in src/qr.jl and the failing cases in test/test_qr.jl, test/test_linearsolve.jl, and test/test_edgecases.jl. Separately inspect the augmented singular path associated with test/test_augmented.jl. Done means the current scpqr API works through the QR paths and singular inputs raise SingularException as asserted, without weakening tests.