[sergo] Sergo Report: 31st-Linter-Delta + Missed Syntactic Holdout - 2026-06-21

[github-actions[bot]]

Executive Summary

Run R43 detected a registry delta (30 → 31 analyzers) — the 31st linter sprintferrorsnew is new this cycle. It audited clean, so the value this run came from a disciplined full re-grep of the syntactic-stdlib-match antipattern: using both Name == pkg and Name != pkg operators surfaced a CI-enforced holdout (tolowerequalfold) that the #40243 migration sweep missed entirely. Two distinct, single-file issues filed. No duplicates.

Tool / Registry Updates

• Serena LSP: 23 tools, stable R4–R43 (serena --help). No tool change.
• Registry delta: cmd/linters/main.go now registers 31 analyzers (lines 54–84) vs 30 in R42.
• 31st linter = sprintferrorsnew — flags errors.New(fmt.Sprintf(...)) that should be fmt.Errorf(...).
• Audited clean ✅ — uses astutil.IsPkgSelector for both errors and fmt (the sg42a2 regression lesson was applied), skips test files, requires exact arg count. The goodVariable (pre-built string var) false-negative is intentional per testdata. No issue warranted.
• doc.go:3 still says "29 active analyzers" — now off-by-2 (omits hardcodedfilepath, sprintferrdot, sprintferrorsnew). Already tracked by open doc-sync: pkg/linters/doc.go says "29 active analyzers" but 30 are registered — list omits hardcodedfilepath and sprintferrdot #40436, skipped as duplicate.

Strategy: Strict 50/50 Split

Cached half — syntactic_stdlib_match (strongest historical land-arg). Re-grepped all 31 linters for ident.Name (== | !=) "<pkg>". Key methodology fix: linters use != for early-return, so a ==-only grep silently misses holdouts. The both-operator grep surfaced a new holdout not in any open issue.

New half — pattern_set_too_narrow (fresh never-audited linter). Deep-read lenstringzero and found an operator-set asymmetry: it flags len(s) != 0 but not the identical idiom len(s) > 0.

Run targets: ≥1 strong cached finding, ≥1 fresh-linter finding, 2 non-duplicate CI-relevant issues. All met.

Findings (2 filed, 1 skipped-dup)

🔴 sg43a1 — tolowerequalfold syntactic strings match (CACHED) → issue filed

pkg/linters/tolowerequalfold/tolowerequalfold.go:255 matches the strings package by ident.Name != "strings" with no type info, in a CI-enforced linter. Causes a shadowing false-positive and an alias-import (import str "strings") false-negative.

Evidence & fix

• isCaseConvCall (line 212) delegates to caseConvArg, so line 255 is the single chokepoint for the whole analyzer.
• sameOperand (line 271) already uses pass.TypesInfo.ObjectOf — type info is available, only the package check was left syntactic.
• astutil is already imported (line 15); fix is replacing ~6 lines with astutil.IsPkgSelector(pass, sel, "strings").
• Missed by Linter precision: migrate the 3 remaining CI-enforced linters that match stdlib packages by identifier name to astutil.IsPkgSele [Content truncated due to length] #40243 — that issue enumerates only osexitinlibrary / fprintlnsprintf / errstringmatch. tolowerequalfold is a distinct CI-enforced holdout.
• Latent today: 0 production aliased/shadowed strings sites — a consistency/future-proofing fix.

🟡 sg43a2 — lenstringzero relational-operator coverage gap (NEW) → issue filed

pkg/linters/lenstringzero/lenstringzero.go:40 only handles token.EQL/token.NEQ. Since len(s) >= 0 always holds, len(s) != 0 and len(s) > 0 are semantically identical, yet only the former is flagged.

Escaping forms & impact

Written	Equivalent	Flagged?
len(s) == 0	s == ""	✅
len(s) != 0	s != ""	✅
len(s) > 0	s != ""	❌
len(s) < 1 / <= 0	s == ""	❌
len(s) >= 1	s != ""	❌

Real string-typed production sites: pkg/stringutil/stringutil.go:44, pkg/stringutil/sanitize.go:209. The narrow scope may be deliberate (>0 is prevalent/noisy) — issue asks the team to either extend coverage or document the boundary, rather than leave the silent asymmetry.

⚪ Skipped (duplicate)

• doc.go off-by-2 — already open as doc-sync: pkg/linters/doc.go says "29 active analyzers" but 30 are registered — list omits hardcodedfilepath and sprintferrdot #40436.

Reconcile Status (issue OPEN ≠ code fixed)

Grepped production code for each prior fix. All syntactic-match migrations remain unlanded:

Issue	Sites	Code state
#40243	osexit:59, fprintln:144, errstring:100	still syntactic — unfixed
#40435	fileclose:172, contextcancel:138	still syntactic — unfixed
#40436	doc.go header	now 29 vs 31 (worse)
#40434	sprintferrdot verb gate	open

Metrics

• Findings: 6 (1 clean-audit, 2 filed, 1 dup-skip, 2 reconcile)
• Issues created: 2 (sg43a1, sg43a2) — both single-file, non-duplicate
• Self-scored success: 9/10 (registry delta caught; methodology fix caught a missed CI-enforced holdout; fresh linter cleared)
• Cumulative: 43 runs, 311 findings, 87 tasks, avg 8.81

Next-Run Focus (R44)

1. Reverify landings of Linter precision: migrate the 3 remaining CI-enforced linters that match stdlib packages by identifier name to astutil.IsPkgSele [Content truncated due to length] #40243 / Linter precision: two newest linters (fileclosenotdeferred, contextcancelnotdeferred) match stdlib packages by identifier name — [Content truncated due to length] #40435 (currently code-still-syntactic) and errstringmatch coverage gap: only strings.Contains(err.Error(), ...) is flagged — HasPrefix/HasSuffix/EqualFold/Index on err.Err [Content truncated due to length] #40244 / jsonmarshalignoredeerror FN: bare-call json.Unmarshal(data, &v) (ExprStmt) discards the error but is never inspected — only As [Content truncated due to length] #39982 / sprintferrdot precision: verb handling {s,v} is wrong in both directions — %#v false positive, %q/%x/%X false negative #40434 / sg43a1-2.
2. After any IsPkgSelector PR lands, re-grep Name (== | !=) with both operators across all 31 linters (new linters keep regressing this).
3. Fresh never-audited targets: errorfwrapv, excessivefuncparams, seenmapbool, errormessage, ossetenvlibrary.
4. Watch for a 32nd-linter delta.

References:

• §27894535793

Generated by 🤖 Sergo - Serena Go Expert · 276.1 AIC · ⌖ 11 AIC · ⊞ 5.8K · ◷

• expires on Jun 21, 2026, 9:30 PM UTC-08:00