Add context to file load failures in pdfium_test.

samples/pdfium_test.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <list>
@@ skipping 372 matching lines @@
 
   if (FPDFAvail_IsLinearized(pdf_avail)) {
     fprintf(stderr, "Linearized path...\n");
     doc = FPDFAvail_GetDocument(pdf_avail, nullptr);
   } else {
     fprintf(stderr, "Non-linearized path...\n");
     doc = FPDF_LoadCustomDocument(&file_access, nullptr);
   }
 
   if (!doc) {
-    fprintf(stderr, "Load pdf docs unsuccessful.\n");
+    unsigned long err = FPDF_GetLastError();
+    fprintf(stderr, "Load pdf docs unsuccessful: ");
+    switch (err) {
+      case FPDF_ERR_SUCCESS:
+        fprintf(stderr, "Success");
+        break;
+      case FPDF_ERR_UNKNOWN:
+        fprintf(stderr, "Unknown error");
+        break;
+      case FPDF_ERR_FILE:
+        fprintf(stderr, "File not found or could not be opened");
+        break;
+      case FPDF_ERR_FORMAT:
+        fprintf(stderr, "File not in PDF format or corrupted");
+        break;
+      case FPDF_ERR_PASSWORD:
+        fprintf(stderr, "Password required or incorrect password");
+        break;
+      case FPDF_ERR_SECURITY:
+        fprintf(stderr, "Unsupported security scheme");
+        break;
+      case FPDF_ERR_PAGE:
+        fprintf(stderr, "Page not found or content error");
+        break;
+      default:
+        fprintf(stderr, "Unknown error %ld", err);
+    }
+    fprintf(stderr, ".\n");
+
     FPDFAvail_Destroy(pdf_avail);
     return;
   }
 
   (void)FPDF_GetDocPermissions(doc);
   (void)FPDFAvail_IsFormAvail(pdf_avail, &hints);
 
   FPDF_FORMHANDLE form = FPDFDOC_InitFormFillEnvironment(doc, &form_callbacks);
   FPDF_SetFormFieldHighlightColor(form, 0, 0xFFE4DD);
   FPDF_SetFormFieldHighlightAlpha(form, 100);
@@ skipping 149 matching lines @@
   }
 
   FPDF_DestroyLibrary();
 #ifdef PDF_ENABLE_V8
   v8::V8::ShutdownPlatform();
   delete platform;
 #endif  // PDF_ENABLE_V8
 
   return 0;
 }