Add support for anon types in FQN generation

This fixes a bug in the fully qualified name generation we encounter a
segment that has no name, such as when a proc is really a C++ lambda
expression, which internally generates an anonymous class to house the
function. In this case, we generate a unique name based on the DIE's
offset to serve as the segment's name.

src/dwarf2pdb.cpp

@@ -735,13 +735,29 @@ void CV2PDB::formatFullyQualifiedProcName(const DWARF_InfoData* proc, char* buf,
 
 	// Format the parents in reverse order with :: operator in between.
 	for (int i = segments.size() - 1; i >= 0; --i) {
-		const int nameLen = strlen(segments[i]->name);
+		const char* name = segments[i]->name;
+		char nameBuf[64] = {};
+		int nameLen = 0;
+		if (!segments[i]->name) {
+			// This segment has no name. This could be because it is part of
+			// an anonymous class, which often happens for lambda expressions.
+			// Generate a unique anonymous name for it.
+			nameLen = sprintf_s(nameBuf, "[anon_%x]", segments[i]->entryOff);
+			if (nameLen < 0) {
+				// Formatting failed. Try a default name.
+				assert(false);  // crash in debug builds.
+				name = "[anon]";
+			}
+			name = nameBuf;
+		} else {
+			nameLen = strlen(name);
+		}
 		if (remain < nameLen) {
 			fprintf(stderr, "unable to fit full proc name: %s\n", proc->name);
 			return;
 		}
 
-		memcpy(p, segments[i]->name, nameLen);
+		memcpy(p, name, nameLen);
 
 		p += nameLen;
 		remain -= nameLen;

src/readDwarf.cpp

@@ -766,7 +766,7 @@ DWARF_InfoData* DIECursor::readNext(DWARF_InfoData* entry, bool stopAtNull)
 			return nullptr; // root of the tree does not have a null terminator, but we know the length
 
 		id.entryPtr = ptr;
-		entryOff = img->debug_info.sectOff(ptr);
+		entryOff = id.entryOff = img->debug_info.sectOff(ptr);
 		id.code = LEB128(ptr);
 
 		// If the previously scanned node claimed to have a child, this must be a valid DIE.

src/readDwarf.h

@@ -191,6 +191,8 @@ struct DWARF_InfoData
 	// Pointer into the memory-mapped image section where this DIE is located.
 	byte* entryPtr;
 
+	unsigned int entryOff = 0;  // the entry offset in the section it is in.
+
 	// Code to find the abbrev entry for this DIE, or 0 if it a sentinel marking
 	// the end of a sibling chain.
 	int code;