Cxx: scan the cork queue instead of the symtab to fill nth fields

Close #3634.

If an enum has so many enumerators, the original code, counting enumerators
for filling nth fields, takes a too long time.

The new code looks up the last enumerator and calculates a new nth value
by incrementing the last nth value.

Signed-off-by: Masatake YAMATO <[email protected]>

Author: masatake

Tmain/c-large-enum.d/exit-expected.txt

@@ -0,0 +1 @@
+0

Tmain/c-large-enum.d/run.sh

@@ -0,0 +1,22 @@
+# Copyright: 2023 Masatake YAMATO
+# License: GPL-2
+
+input=/tmp/c-large-enum.d-input.c
+CTAGS="$1 --quiet --options=NONE"
+
+i=0
+{
+	echo "enum E {"
+	while [ $i -lt 32770 ]; do
+		printf "X%x," $i
+		i=$(($i + 1))
+	done
+	echo "};"
+} > $input
+
+${CTAGS} --sort=no -n --fields= --fields=+"{nth}" -x --_xformat='%{name} %{nth}' "$input" | tail -10
+r=$?
+
+rm -f "$input"
+
+exit $r

Tmain/c-large-enum.d/stderr-expected.txt

@@ -0,0 +1,10 @@
+X7ff8 32760
+X7ff9 32761
+X7ffa 32762
+X7ffb 32763
+X7ffc 32764
+X7ffd 32765
+X7ffe 32766
+X7fff 32767
+X8000 32767
+X8001 32767

Tmain/c-large-enum.d/stdout-expected.txt

@@ -275,12 +275,28 @@ void cxxTagUseTokensInRangeAsPartOfDefTags(int iCorkIndex, CXXToken * pFrom, CXX
 	}
 }
 
-static bool countSameKindEntry(int corkIndex,
-							   tagEntryInfo * entry,
-							   void * data)
+static short cxxTagLookBackLastNth(langType iLangType, int iScopeIndex, unsigned int uKind)
 {
-	unsigned int *uKind = data;
-	return (entry->kindIndex == *uKind);
+	for (size_t uCount = countEntryInCorkQueue (); uCount > (CORK_NIL + 1); uCount--)
+	{
+		int iCorkIndex = (int)(uCount - 1);
+		tagEntryInfo *pTag = getEntryInCorkQueue(iCorkIndex);
+		if (iCorkIndex == iScopeIndex)
+			return 0;
+		else if (pTag->extensionFields.scopeIndex == iScopeIndex
+				 && pTag->langType == iLangType
+				 && pTag->kindIndex == uKind)
+		{
+			return pTag->extensionFields.nth + (
+				/* Over-wrapped; if the value is too large for sizeof(nth),
+				 * Don't increment more. */
+				((short)(pTag->extensionFields.nth + 1) > 0)
+				? 1
+				: 0
+				);
+		}
+	}
+	return NO_NTH_FIELD;
 }
 
 tagEntryInfo * cxxTagBegin(unsigned int uKind,CXXToken * pToken)
@@ -315,10 +331,9 @@ tagEntryInfo * cxxTagBegin(unsigned int uKind,CXXToken * pToken)
 		{
 			if (uKind == CXXTagKindMEMBER || uKind == CXXTagKindENUMERATOR
 				|| uKind == CXXTagKindPARAMETER || uKind == CXXTagCPPKindTEMPLATEPARAM)
-				g_oCXXTag.extensionFields.nth =
-					(short) countEntriesInScope(g_oCXXTag.extensionFields.scopeIndex,
-												true,
-												countSameKindEntry, &uKind);
+				g_oCXXTag.extensionFields.nth = cxxTagLookBackLastNth(g_oCXXTag.langType,
+																	  g_oCXXTag.extensionFields.scopeIndex,
+																	  uKind);
 		}
 	}