Test for direct, rather than resolved nulls in parser

Just because we know an indirect reference is null, doesn't mean we
shouldn't keep it indirect.

ChangeLog

@@ -1,5 +1,9 @@
 2019-08-22  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add QPDFObjectHandle::isDirectNull() -- a const method that
+	allows determining whether an object is a literal null without
+	attempting to resolve it.
+
 	* Stop replacing indirect references to null with literal null in
 	arrays when writing output with QPDFWriter.
 

include/qpdf/QPDFObjectHandle.hh

@@ -281,13 +281,12 @@ class QPDFObjectHandle
     QPDF_DLL
     bool isReserved();
 
-    // True for objects that are direct nulls or have previously been
+    // True for objects that are direct nulls. Does not attempt to
-    // resolved to be nulls. Does not attempt to resolve objects. This
+    // resolve objects. This is intended for internal use, but it can
-    // is intended for internal use, but it can be used as an
+    // be used as an efficient way to check for nulls that are not
-    // efficient way to check for nulls if you don't mind unresolved
+    // indirect objects.
-    // indirect nulls being false negatives.
     QPDF_DLL
-    bool isResolvedNull() const;
+    bool isDirectNull() const;
 
     // This returns true in addition to the query for the specific
     // type for indirect objects.

libqpdf/QPDFObjectHandle.cc

@@ -263,9 +263,10 @@ QPDFObjectHandle::isBool()
 }
 
 bool
-QPDFObjectHandle::isResolvedNull() const
+QPDFObjectHandle::isDirectNull() const
 {
-    return QPDFObjectTypeAccessor<QPDF_Null>::check(m->obj.getPointer());
+    return (this->m->initialized && (this->m->objid == 0) &&
+            QPDFObjectTypeAccessor<QPDF_Null>::check(m->obj.getPointer()));
 }
 
 bool

libqpdf/SparseOHArray.cc

@@ -15,7 +15,7 @@ SparseOHArray::size() const
 void
 SparseOHArray::append(QPDFObjectHandle oh)
 {
-    if (! oh.isResolvedNull())
+    if (! oh.isDirectNull())
     {
         this->elements[this->n_elements] = oh;
     }
@@ -73,7 +73,7 @@ SparseOHArray::setAt(size_t idx, QPDFObjectHandle oh)
     {
 	throw std::logic_error("bounds error setting item in SparseOHArray");
     }
-    if (oh.isResolvedNull())
+    if (oh.isDirectNull())
     {
         this->elements.erase(idx);
     }

qpdf/qtest/qpdf.test

@@ -2456,6 +2456,7 @@ my @goodfiles = ("implicit null",			# 1
 		 "hybrid xref old mode",		# 18
 		 "xref with prev",			# 19
 		 "lots of compressible objects",	# 20
+                 "array with indirect nulls",           # 21
 		 );
 
 $n_tests += (3 * @goodfiles) + 6;

qpdf/qtest/qpdf/good21.out

@@ -0,0 +1,11 @@
+/QTest is indirect and has type array (8)
+/QTest is an array with 6 items
+  item 0 is direct
+  item 1 is direct
+  item 2 is direct
+  item 3 is indirect
+  item 4 is direct
+  item 5 is indirect
+unparse: 9 0 R
+unparseResolved: [ /literal null /indirect 8 0 R /undefined 10 0 R ]
+test 1 done

qpdf/qtest/qpdf/good21.pdf

@@ -0,0 +1,106 @@
+%PDF-1.3
+%¿÷¢þ
+%QDF-1.0
+
+1 0 obj
+<<
+  /Pages 2 0 R
+  /Type /Catalog
+>>
+endobj
+
+2 0 obj
+<<
+  /Count 1
+  /Kids [
+    3 0 R
+  ]
+  /Type /Pages
+>>
+endobj
+
+%% Page 1
+3 0 obj
+<<
+  /Contents 4 0 R
+  /MediaBox [
+    0
+    0
+    612
+    792
+  ]
+  /Parent 2 0 R
+  /Resources <<
+    /Font <<
+      /F1 6 0 R
+    >>
+    /ProcSet 7 0 R
+  >>
+  /Type /Page
+>>
+endobj
+
+%% Contents for page 1
+4 0 obj
+<<
+  /Length 5 0 R
+>>
+stream
+BT
+  /F1 24 Tf
+  72 720 Td
+  (Potato) Tj
+ET
+endstream
+endobj
+
+5 0 obj
+44
+endobj
+
+6 0 obj
+<<
+  /BaseFont /Helvetica
+  /Encoding /WinAnsiEncoding
+  /Name /F1
+  /Subtype /Type1
+  /Type /Font
+>>
+endobj
+
+7 0 obj
+[
+  /PDF
+  /Text
+]
+endobj
+
+8 0 obj
+null
+endobj
+
+9 0 obj
+[ /literal null /indirect 8 0 R /undefined 10 0 R ]
+endobj
+
+xref
+0 10
+0000000000 65535 f 
+0000000025 00000 n 
+0000000079 00000 n 
+0000000161 00000 n 
+0000000376 00000 n 
+0000000475 00000 n 
+0000000494 00000 n 
+0000000612 00000 n 
+0000000647 00000 n 
+0000000668 00000 n 
+trailer <<
+  /Root 1 0 R
+  /Size 10
+  /QTest 9 0 R
+  /ID [<06c2c8fc54c5f9cc9246898e1e1a7146><06c2c8fc54c5f9cc9246898e1e1a7146>]
+>>
+startxref
+736
+%%EOF

qpdf/qtest/qpdf/good21.qdf

@@ -0,0 +1,127 @@
+%PDF-1.3
+%¿÷¢þ
+%QDF-1.0
+
+%% Original object ID: 1 0
+1 0 obj
+<<
+  /Pages 3 0 R
+  /Type /Catalog
+>>
+endobj
+
+%% Original object ID: 9 0
+2 0 obj
+[
+  /literal
+  null
+  /indirect
+  4 0 R
+  /undefined
+  5 0 R
+]
+endobj
+
+%% Original object ID: 2 0
+3 0 obj
+<<
+  /Count 1
+  /Kids [
+    6 0 R
+  ]
+  /Type /Pages
+>>
+endobj
+
+%% Original object ID: 8 0
+4 0 obj
+null
+endobj
+
+%% Original object ID: 10 0
+5 0 obj
+null
+endobj
+
+%% Page 1
+%% Original object ID: 3 0
+6 0 obj
+<<
+  /Contents 7 0 R
+  /MediaBox [
+    0
+    0
+    612
+    792
+  ]
+  /Parent 3 0 R
+  /Resources <<
+    /Font <<
+      /F1 9 0 R
+    >>
+    /ProcSet 10 0 R
+  >>
+  /Type /Page
+>>
+endobj
+
+%% Contents for page 1
+%% Original object ID: 4 0
+7 0 obj
+<<
+  /Length 8 0 R
+>>
+stream
+BT
+  /F1 24 Tf
+  72 720 Td
+  (Potato) Tj
+ET
+endstream
+endobj
+
+8 0 obj
+44
+endobj
+
+%% Original object ID: 6 0
+9 0 obj
+<<
+  /BaseFont /Helvetica
+  /Encoding /WinAnsiEncoding
+  /Name /F1
+  /Subtype /Type1
+  /Type /Font
+>>
+endobj
+
+%% Original object ID: 7 0
+10 0 obj
+[
+  /PDF
+  /Text
+]
+endobj
+
+xref
+0 11
+0000000000 65535 f 
+0000000052 00000 n 
+0000000133 00000 n 
+0000000239 00000 n 
+0000000338 00000 n 
+0000000387 00000 n 
+0000000445 00000 n 
+0000000688 00000 n 
+0000000787 00000 n 
+0000000833 00000 n 
+0000000978 00000 n 
+trailer <<
+  /QTest 2 0 R
+  /Root 1 0 R
+  /Size 11
+  /ID [<06c2c8fc54c5f9cc9246898e1e1a7146><31415926535897932384626433832795>]
+>>
+startxref
+1014
+%%EOF