github · pelikhan · Jun 21, 2026 · Jun 21, 2026 · Jun 21, 2026 · Jun 21, 2026
diff --git a/docs/adr/40621-extend-lenstringzero-to-relational-len-string-comparisons.md b/docs/adr/40621-extend-lenstringzero-to-relational-len-string-comparisons.md
@@ -0,0 +1,38 @@
+# ADR-40621: Extend `lenstringzero` linter to relational len-string comparisons
+
+**Date**: 2026-06-21
+**Status**: Draft
+
+## Context
+
+The `lenstringzero` linter flags `len(s) == 0` and `len(s) != 0` comparisons on string values, suggesting the clearer `s == ""` / `s != ""` forms. It silently missed the semantically identical *relational* idioms — most notably `len(s) > 0`, which is arguably the most common non-empty-string test in Go, plus `len(s) >= 1`, `len(s) < 1`, and `len(s) <= 0`, including their yoda-order variants (`0 < len(s)`). This left a real coverage gap: the linter's stated purpose (steer string emptiness checks toward direct comparison) was only partially enforced. The implementation matches strings syntactically over the AST and must avoid flagging non-string slices, tautologies (`len(s) >= 0`), and contradictions (`len(s) < 0`).
+
+## Decision
+
+We will extend `lenstringzero` to recognize all six comparison operators (`==`, `!=`, `>`, `>=`, `<`, `<=`) against the integer literals `0` and `1`, in both normal and yoda operand order. A new `matchLenLiteralExpr` normalizes each comparison so `len` is on the left and reports the literal; `resolveFixOp` maps the normalized `(operator, literal)` pair to the correct fix (`==`/`!=`) and verb (`empty`/`non-empty`), and explicitly excludes tautologies and contradictions. `buildLenStringFix` now takes an explicit `fixOp` so relational inputs still emit a correct direct-comparison suggested fix, and diagnostics report the normalized form even for yoda input. This keeps the linter's syntactic, fix-emitting design while closing the idiom gap.
+
+## Alternatives Considered
+
+### Alternative 1: Keep scope limited to `==` / `!=`
+Leave the linter as-is and rely on reviewers to catch relational forms. Rejected because `len(s) > 0` is the single most common non-empty idiom, so the linter was missing its highest-value target while appearing complete.
+
+### Alternative 2: Type/SSA-based semantic analysis instead of syntactic pattern tables
+Use a more general value-analysis approach to recognize emptiness comparisons regardless of literal or operator shape. Rejected as disproportionate: it adds significant complexity and analysis cost for a linter whose value comes from a small, well-known set of literal idioms that an explicit `(operator, literal)` table covers precisely and predictably.
+
+## Consequences
+
+### Positive
+- Catches the most common non-empty-string idiom (`len(s) > 0`) and its relatives, including yoda order.
+- Every flagged relational case still ships a correct auto-applicable suggested fix.
+
+### Negative
+- More surface area and branching (`matchLenLiteralExpr`, `resolveFixOp`, `flipOp`, `isIntOne`) to maintain and reason about.
+- Coverage is deliberately bounded to literals `0` and `1`; other meaningful thresholds (e.g. `len(s) > 1`) are out of scope and not flagged.
+
+### Neutral
+- Diagnostic messages now normalize yoda input to `len`-on-left form, so reported text can differ from the source spelling.
+- Tautologies (`len(s) >= 0`) and contradictions (`len(s) < 0`) are intentionally left unflagged rather than rewritten.
+
+---
+
+*This is a DRAFT ADR generated by the [Design Decision Gate](https://github.com/github/gh-aw/actions/runs/27907011489) workflow. The PR author must review, complete, and finalize this document before the PR can merge.*
diff --git a/pkg/linters/lenstringzero/lenstringzero.go b/pkg/linters/lenstringzero/lenstringzero.go
@@ -1,5 +1,6 @@
-// Package lenstringzero implements a Go analysis linter that flags len(s) == 0
-// and len(s) != 0 comparisons on string values that should use == "" or != "" instead.
+// Package lenstringzero implements a Go analysis linter that flags len(s) == 0,
+// len(s) != 0, and equivalent relational comparisons (len(s) > 0, len(s) >= 1,
+// len(s) < 1, len(s) <= 0) on string values that should use == "" or != "" instead.
 package lenstringzero
 
 import (
@@ -16,8 +17,10 @@ import (
 )
 
 var Analyzer = &analysis.Analyzer{
-	Name:     "lenstringzero",
-	Doc:      "reports len(s) == 0 and len(s) != 0 comparisons on string values that should use == \"\" or != \"\" instead",
+	Name: "lenstringzero",
+	Doc: "reports len(s) == 0, len(s) != 0, and equivalent relational comparisons " +
+		"(len(s) > 0, len(s) >= 1, len(s) < 1, len(s) <= 0) on string values " +
+		"that should use == \"\" or != \"\" instead",
 	URL:      "https://github.com/github/gh-aw/tree/main/pkg/linters/lenstringzero",
 	Requires: []*analysis.Analyzer{inspect.Analyzer},
 	Run:      run,
@@ -37,7 +40,9 @@ func run(pass *analysis.Pass) (any, error) {
 		if !ok {
 			return
 		}
-		if expr.Op != token.EQL && expr.Op != token.NEQ {
+		switch expr.Op {
+		case token.EQL, token.NEQ, token.GTR, token.GEQ, token.LSS, token.LEQ:
+		default:
 			return
 		}
 
@@ -46,24 +51,13 @@ func run(pass *analysis.Pass) (any, error) {
 			return
 		}
 
-		var lenArg ast.Expr
-		isDirect := false
-		if isLenCall(expr.X) && isIntZero(expr.Y) {
-			lenArg = lenCallArg(expr.X)
-			isDirect = true
-		} else if isIntZero(expr.X) && isLenCall(expr.Y) {
-			lenArg = lenCallArg(expr.Y)
-			isDirect = true
-		} else if isIntZero(expr.Y) {
-			if arg, ok := lenAliasArg(pass, expr.X, lenStringAliases); ok {
-				lenArg = arg
-			}
-		} else if isIntZero(expr.X) {
-			if arg, ok := lenAliasArg(pass, expr.Y, lenStringAliases); ok {
-				lenArg = arg
-			}
+		lenArg, isDirect, normalOp, lit, matched := matchLenLiteralExpr(pass, expr, lenStringAliases)
+		if !matched {
+			return
 		}
-		if lenArg == nil {
+
+		fixOp, cmpVerb, valid := resolveFixOp(normalOp, lit)
+		if !valid {
 			return
 		}
 
@@ -76,36 +70,127 @@ func run(pass *analysis.Pass) (any, error) {
 			return
 		}
 
-		op := expr.Op.String()
-		var cmpVerb string
-		if expr.Op == token.EQL {
-			cmpVerb = "empty"
-		} else {
-			cmpVerb = "non-empty"
-		}
 		var fixes []analysis.SuggestedFix
 		if isDirect {
-			fixes = buildLenStringFix(pass, expr, lenArg)
+			fixes = buildLenStringFix(pass, expr, lenArg, fixOp)
 		}
 		pass.Report(analysis.Diagnostic{
 			Pos:            expr.Pos(),
 			End:            expr.End(),
-			Message:        fmt.Sprintf(`use s %s "" to check for %s string instead of len(s) %s 0`, op, cmpVerb, op),
+			Message:        fmt.Sprintf(`use s %s "" to check for %s string instead of len(s) %s %d`, fixOp, cmpVerb, normalOp, lit),
 			SuggestedFixes: fixes,
 		})
 	})
 
 	return nil, nil
 }
 
-// buildLenStringFix returns a SuggestedFix that rewrites a direct len(s) == 0
-// or len(s) != 0 comparison to s == "" or s != "".
-func buildLenStringFix(pass *analysis.Pass, expr *ast.BinaryExpr, lenArg ast.Expr) []analysis.SuggestedFix {
+// matchLenLiteralExpr tries to match len(s)/alias OP literal or literal OP len(s)/alias.
+// Returns (lenArg, isDirect, normalOp, lit, matched) where:
+//   - lenArg is the string expression passed to len()
+//   - isDirect indicates a direct len() call (true) vs a stored alias (false)
+//   - normalOp is the operator normalized so that len is on the left side
+//   - lit is the integer literal value (0 or 1)
+//   - matched indicates whether a valid pattern was found
+func matchLenLiteralExpr(pass *analysis.Pass, expr *ast.BinaryExpr, aliases map[types.Object]ast.Expr) (lenArg ast.Expr, isDirect bool, normalOp token.Token, lit int, ok bool) {
+	op := expr.Op
+
+	// Normal order: len/alias on the left, literal on the right.
+	if isLenCall(expr.X) {
+		if isIntZero(expr.Y) {
+			return lenCallArg(expr.X), true, op, 0, true
+		}
+		if isIntOne(expr.Y) {
+			return lenCallArg(expr.X), true, op, 1, true
+		}
+	}
+	if isIntZero(expr.Y) {
+		if arg, ok2 := lenAliasArg(pass, expr.X, aliases); ok2 {
+			return arg, false, op, 0, true
+		}
+	}
+	if isIntOne(expr.Y) {
+		if arg, ok2 := lenAliasArg(pass, expr.X, aliases); ok2 {
+			return arg, false, op, 1, true
+		}
+	}
+
+	// Yoda order: literal on the left, len/alias on the right.
+	// Flip the operator so the normalized form has len on the left.
+	if isLenCall(expr.Y) {
+		if isIntZero(expr.X) {
+			return lenCallArg(expr.Y), true, flipOp(op), 0, true
+		}
+		if isIntOne(expr.X) {
+			return lenCallArg(expr.Y), true, flipOp(op), 1, true
+		}
+	}
+	if isIntZero(expr.X) {
+		if arg, ok2 := lenAliasArg(pass, expr.Y, aliases); ok2 {
+			return arg, false, flipOp(op), 0, true
+		}
+	}
+	if isIntOne(expr.X) {
+		if arg, ok2 := lenAliasArg(pass, expr.Y, aliases); ok2 {
+			return arg, false, flipOp(op), 1, true
+		}
+	}
+
+	return nil, false, 0, 0, false
+}
+
+// resolveFixOp returns the fix operator and comparison verb for a normalized
+// comparison where len is on the left side.
+// Only the semantically meaningful cases are flagged:
+//
+//	len(s) == 0  →  s == ""   (empty)
+//	len(s) != 0  →  s != ""   (non-empty)
+//	len(s) > 0   →  s != ""   (non-empty)
+//	len(s) >= 1  →  s != ""   (non-empty)
+//	len(s) < 1   →  s == ""   (empty)
+//	len(s) <= 0  →  s == ""   (empty)
+//
+// Tautologies (len(s) >= 0) and contradictions (len(s) < 0) are not flagged.
+func resolveFixOp(normalOp token.Token, lit int) (fixOp token.Token, cmpVerb string, ok bool) {
+	switch normalOp {
+	case token.EQL:
+		if lit == 0 {
+			return token.EQL, "empty", true
+		}
+	case token.NEQ:
+		if lit == 0 {
+			return token.NEQ, "non-empty", true
+		}
+	case token.GTR:
+		if lit == 0 {
+			return token.NEQ, "non-empty", true
+		}
+	case token.GEQ:
+		if lit == 1 {
+			return token.NEQ, "non-empty", true
+		}
+		// lit == 0 → len(s) >= 0 is always true; do not flag.
+	case token.LSS:
+		if lit == 1 {
+			return token.EQL, "empty", true
+		}
+		// lit == 0 → len(s) < 0 is always false; do not flag.
+	case token.LEQ:
+		if lit == 0 {
+			return token.EQL, "empty", true
+		}
+	}
+	return 0, "", false
+}
+
+// buildLenStringFix returns a SuggestedFix that rewrites a direct len(s) comparison
+// to a direct string comparison using fixOp (== or !=).
+func buildLenStringFix(pass *analysis.Pass, expr *ast.BinaryExpr, lenArg ast.Expr, fixOp token.Token) []analysis.SuggestedFix {
 	text := astutil.NodeText(pass.Fset, lenArg)
 	if text == "" {
 		return nil
 	}
-	replacement := fmt.Sprintf(`%s %s ""`, text, expr.Op.String())
+	replacement := fmt.Sprintf(`%s %s ""`, text, fixOp.String())
 	return []analysis.SuggestedFix{{
 		Message: "Replace with direct string comparison",
 		TextEdits: []analysis.TextEdit{{
@@ -116,6 +201,23 @@ func buildLenStringFix(pass *analysis.Pass, expr *ast.BinaryExpr, lenArg ast.Exp
 	}}
 }
 
+// flipOp returns the comparison operator adjusted for swapping left and right operands.
+// For example, when converting "0 < len(s)" to the normalized "len(s) > 0", LSS becomes GTR.
+func flipOp(op token.Token) token.Token {
+	switch op {
+	case token.LSS:
+		return token.GTR
+	case token.GTR:
+		return token.LSS
+	case token.LEQ:
+		return token.GEQ
+	case token.GEQ:
+		return token.LEQ
+	default:
+		return op
+	}
+}
+
 func isLenCall(expr ast.Expr) bool {
 	call, ok := expr.(*ast.CallExpr)
 	if !ok || len(call.Args) != 1 {
@@ -138,6 +240,11 @@ func isIntZero(expr ast.Expr) bool {
 	return ok && lit.Kind == token.INT && lit.Value == "0"
 }
 
+func isIntOne(expr ast.Expr) bool {
+	lit, ok := expr.(*ast.BasicLit)
+	return ok && lit.Kind == token.INT && lit.Value == "1"
+}
+
 func collectLenStringAliases(pass *analysis.Pass) map[types.Object]ast.Expr {
 	aliases := make(map[types.Object]ast.Expr)
 	for _, file := range pass.Files {

diff --git a/pkg/linters/lenstringzero/testdata/src/lenstringzero/lenstringzero.go b/pkg/linters/lenstringzero/testdata/src/lenstringzero/lenstringzero.go
@@ -32,7 +32,50 @@ func arrayNotFlagged(s [1]byte) bool {
 	return len(s) != 0
 }
 
-func lenNotZeroOp(s string) bool {
+func lenGreaterThanZero(s string) bool {
+	return len(s) > 0 // want `use s != "" to check for non-empty string instead of len\(s\) > 0`
+}
+
+func lenGreaterOrEqualOne(s string) bool {
+	return len(s) >= 1 // want `use s != "" to check for non-empty string instead of len\(s\) >= 1`
+}
+
+func lenLessThanOne(s string) bool {
+	return len(s) < 1 // want `use s == "" to check for empty string instead of len\(s\) < 1`
+}
+
+func lenLessOrEqualZero(s string) bool {
+	return len(s) <= 0 // want `use s == "" to check for empty string instead of len\(s\) <= 0`
+}
+
+func yodaLenGreaterThanZero(s string) bool {
+	return 0 < len(s) // want `use s != "" to check for non-empty string instead of len\(s\) > 0`
+}
+
+func yodaLenGreaterOrEqualOne(s string) bool {
+	return 1 <= len(s) // want `use s != "" to check for non-empty string instead of len\(s\) >= 1`
+}
+
+func yodaLenLessThanOne(s string) bool {
+	return 1 > len(s) // want `use s == "" to check for empty string instead of len\(s\) < 1`
+}
+
+func yodaLenLessOrEqualZero(s string) bool {
+	return 0 >= len(s) // want `use s == "" to check for empty string instead of len\(s\) <= 0`
+}
+
+// len(s) >= 0 is always true — must not be flagged.
+func lenAlwaysTrue(s string) bool {
+	return len(s) >= 0
+}
+
+// len(s) < 0 is always false — must not be flagged.
+func lenAlwaysFalse(s string) bool {
+	return len(s) < 0
+}
+
+// Non-string slice must not be flagged for relational operators.
+func sliceGreaterThanZeroNotFlagged(s []byte) bool {
 	return len(s) > 0
 }
 
@@ -50,6 +93,26 @@ func aliasNotEmpty(s string) bool {
 	return n != 0 // want `use s != "" to check for non-empty string instead of len\(s\) != 0`
 }
 
+func aliasGreaterThanZero(s string) bool {
+	n := len(s)
+	return n > 0 // want `use s != "" to check for non-empty string instead of len\(s\) > 0`
+}
+
+func aliasGreaterOrEqualOne(s string) bool {
+	n := len(s)
+	return n >= 1 // want `use s != "" to check for non-empty string instead of len\(s\) >= 1`
+}
+
+func aliasLessThanOne(s string) bool {
+	n := len(s)
+	return n < 1 // want `use s == "" to check for empty string instead of len\(s\) < 1`
+}
+
+func aliasLessOrEqualZero(s string) bool {
+	n := len(s)
+	return n <= 0 // want `use s == "" to check for empty string instead of len\(s\) <= 0`
+}
+
 func aliasReassignedNotFlagged(s string) bool {
 	n := len(s)
 	n = 1
@@ -71,3 +134,4 @@ func arrayAliasNotFlagged(s [1]byte) bool {
 	n := len(s)
 	return n == 0
 }
+