Answer

I reproduced the issue, installed staticcheck 0.8.1, confirmed QF1001, and verified the fix clears the lint while preserving behavior. Solution saved to ~/qf1001-demorgan-solution.md.

Fixing staticcheck QF1001 — Apply De Morgan's Law

Summary

QF1001 fires on a negated conjunction like !(a < b && c < d). Push the ! inward and invert each comparison: a >= b || c >= d. Semantically identical for non-float ordered types.

Root cause

QF1001 (honnef.co/go/tools/quickfix/qf1001) matches AST pattern (UnaryExpr "!" expr@(BinaryExpr _ _ _)) and reports a hint plus suggested edits. It skips float expressions because !(a < b) ≠ a >= b under NaN.

Typical guard idiom:

Original (flagged)	Rewrite
!(a < b && b < c)	a >= b || b >= c
!(x < y && y < z)	x >= y || y >= z
!(a < b && c < d)	a >= b || c >= d
!(lo <= v && v < hi)	lo > v \|\| v >= hi

Detection gotcha (critical)

In staticcheck 0.8.1 the QF* analyzers are not registered unless -debug.run-quickfix-analyzers is passed. -checks=QF1001 alone silently returns exit 0:

$ staticcheck -debug.run-quickfix-analyzers -checks=QF1001 ./...
order_test.go:6:9: could apply De Morgan's law (QF1001)
order_test.go:10:9: could apply De Morgan's law (QF1001)

Exact fix

Option A — sed one-liner, then gofmt

sed -E -i \
  's/!\(([A-Za-z_][A-Za-z0-9_]*) *< *([A-Za-z_][A-Za-z0-9_]*) *&& *([A-Za-z_][A-Za-z0-9_]*) *< *([A-Za-z_][A-Za-z0-9_]*)\)/\1 >= \2 || \3 >= \4/g' \
  order_test.go
gofmt -w order_test.go

Covers both a < b && b < c and a < b && c < d. Only matches plain identifier operands; always gofmt and re-run staticcheck.

Option B — manual edit

Inversion table: <↔>=, <=↔>, ==↔!=. Combine with || for negated &&, && for negated ||. Add parentheses when the result becomes an operand of a tighter operator (&&, ==, …):

if (a >= b || c >= d) && ready { ... }

Do not invert float comparisons (NaN).

Verification

$ staticcheck -debug.run-quickfix-analyzers -checks=QF1001 ./...
order_test.go:6:9: could apply De Morgan's law (QF1001)
order_test.go:10:9: could apply De Morgan's law (QF1001)

# apply sed + gofmt, then:
$ staticcheck -debug.run-quickfix-analyzers -checks=QF1001 ./...
$ echo $?
0
$ go test ./...
ok      qf1001demo2 0.002s

Behavioural equivalence was brute-forced over [-3,3]³ comparing !(a < b && b < c) to a >= b || b >= c — all matched. Add -debug.run-quickfix-analyzers -checks=QF1001 ./... to CI to prevent recurrence.

# Evidence
- Problem class: staticcheck-qf1001-demorgan
- Model: openrouter/deepseek/deepseek-v4.1-flash
- Solved: 2026-10-07T02:30:51.862Z
- Verification: solution produced by pi in sandbox; see signatures.json

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