fix: Add support for c++23 elifdef and elifndef

README.md

@@ -1,6 +1,6 @@
 # A compiler front end for the C++ language
 
-This repository contains a _work in progress_ compiler front end for C++ 20.
+This repository contains a _work in progress_ compiler front end for C++ 23.
 
 ## Install
 
@@ -25,7 +25,7 @@ https://robertoraggi.github.io/cplusplus/
 On Linux, macOS and Windows:
 
 ```sh
-# install the python packages required to run the unit tests
+# install the python packages required to run the unit tests (optional)
 pip install -r tests/unit_tests/requirements.txt
 
 # configure the source code

src/parser/cxx/preprocessor.cc

@@ -918,6 +918,30 @@ void Preprocessor::Private::expand(
             setState(std::tuple(true, evaluating));
           }
         }
+      } else if (matchId(ts, "elifdef")) {
+        if (!evaluating) {
+          setState(std::tuple(true, false));
+        } else {
+          const Macro *macro = nullptr;
+          const auto value = lookupMacro(ts->head, macro);
+          if (value) {
+            setState(std::tuple(!evaluating, false));
+          } else {
+            setState(std::tuple(true, evaluating));
+          }
+        }
+      } else if (matchId(ts, "elifndef")) {
+        if (!evaluating) {
+          setState(std::tuple(true, false));
+        } else {
+          const Macro *macro = nullptr;
+          const auto value = lookupMacro(ts->head, macro);
+          if (!value) {
+            setState(std::tuple(!evaluating, false));
+          } else {
+            setState(std::tuple(true, evaluating));
+          }
+        }
       } else if (matchId(ts, "else")) {
         setState(std::tuple(!evaluating, false));
       } else if (matchId(ts, "endif")) {
@@ -1231,6 +1255,7 @@ auto Preprocessor::Private::constantExpression(const TokList *ts) -> long {
 }
 
 auto Preprocessor::Private::conditionalExpression(const TokList *&ts) -> long {
+  if (!ts) return 0;
   const auto value = binaryExpression(ts);
   if (!match(ts, TokenKind::T_QUESTION)) return value;
   const auto iftrue = conditionalExpression(ts);

tests/unit_tests/preprocessor/elifdef_001.cc

@@ -0,0 +1,41 @@
+// RUN: %cxx -E %s -o - | %filecheck %s
+
+#define B
+
+#ifdef A
+int a_not_reachable;
+#elifdef B
+int b_reachable;
+#elifdef C
+int c_not_reachable;
+#else
+int else_not_reachable;
+#endif
+
+// CHECK: b_reachable;
+
+#ifdef AA
+int aa_not_reachable;
+#elifndef BB
+int bb_reachable;
+#elifndef CC
+int cc_not_reachable;
+#elifdef DD
+int dd_not_reachable;
+#else
+int else_not_reachable;
+#endif
+
+// CHECK: bb_reachable;
+
+#ifdef AAA
+int aaa_not_reachable;
+#elifdef BBB
+int bbb_not_reachable;
+#elifdef CCC
+int ccc_not_reachable;
+#else
+int else_reachable;
+#endif
+
+// CHECK: else_reachable;