formatter: avoid blank before sole returns

Do not insert the blank-before-return separator when a return is the
only statement in its block. This keeps compact guard clauses from
gaining an empty line just because the return call wraps across
multiple lines.

Preserve the existing separator behavior for leading comments attached
to the return. Add a focused regression for the wrapped fmt.Errorf
shape seen in adoption diffs.

Author: bhandras

dsl/condition.go

@@ -2113,6 +2113,19 @@ func (c *IsReturnNeedingBlankCond) Eval(caps Captures, ctx *Context) bool {
 	if !ok {
 		return false
 	}
+	if block, ok := ctx.Parent(node).(*ast.BlockStmt); ok &&
+		block != nil && len(block.List) == 1 && block.List[0] == node {
+
+		brace := ctx.Fset.Position(block.Lbrace).Offset
+		returnStart := ctx.Fset.Position(node.Pos()).Offset
+		if brace >= 0 && brace+1 <= returnStart {
+			gap := string(ctx.Source[brace+1 : returnStart])
+			if !strings.Contains(gap, "//") &&
+				!strings.Contains(gap, "/*") {
+				return false
+			}
+		}
+	}
 
 	pos := ctx.Fset.Position(node.Pos())
 	nodeStart := pos.Offset

formatter/pipeline_dsl_blanklines_extras_test.go

@@ -169,4 +169,49 @@ func record() {}
 	require.NoError(t, err)
 }
 
+func TestDSLBlankLinesNative_DoesNotBlankBeforeOnlyWrappedReturn(t *testing.T) {
+	const in = `package p
+
+import "fmt"
+
+func f(i int, childIdx uint32) error {
+	if childIdx <= uint32(i) {
+		return fmt.Errorf("node[%d] child index "+
+			"%d must be > parent index (cycle or "+
+			"back-reference)", i, childIdx)
+	}
+
+	return nil
+}
+`
+
+	p := NewPipeline(
+		PipelineConfig{
+			ColumnLimit:            80,
+			TabStop:                8,
+			UseDSLLogCalls:         true,
+			UseDSLBlankLines:       true,
+			UseDSLBlankLinesNative: true,
+		},
+	)
+
+	first := p.Format([]byte(in))
+	second := p.Format(first)
+	require.Equal(t, string(first), string(second))
+
+	out := string(first)
+	require.Contains(
+		t, out,
+		"if childIdx <= uint32(i) {\n		return fmt.Errorf(",
+	)
+	require.NotContains(
+		t, out,
+		"if childIdx <= uint32(i) {\n\n		return fmt.Errorf(",
+	)
+
+	fset := token.NewFileSet()
+	_, err := parser.ParseFile(fset, "out.go", first, parser.AllErrors)
+	require.NoError(t, err)
+}
+
 // Note: legacy/parity profiles were removed; llformat is next-only.