For the last three years a 45-year-old man had been suffering from dry cough, progressing dyspnea, pulmonary failure, and rapid weight loss. Autopsy of his body shows cor pulmonale. The lungs are markedly fibrotis, with cavities that resemble a honeycomb pattern. Histology revealed interstitial fibrosis and marked lymphohistiocytic stromal infiltration with neutrophilic admixture. Make the diagnosis: