From dcf37af75e8a97c24c85b5a08d2e2b06b28be4bd Mon Sep 17 00:00:00 2001
From: belliash <belliash@codingworkshop.eu.org>
Date: Fri, 21 Jun 2019 00:34:41 +0200
Subject: [PATCH] Implement a NULL-coalescing '??' operator.

---
 engine/parser.c  | 28 +++++++++++++++++++++++++++-
 engine/vm.c      | 13 +++++++++++++
 include/ph7int.h |  2 ++
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/engine/parser.c b/engine/parser.c
index 7f4504c..c73c9bb 100644
--- a/engine/parser.c
+++ b/engine/parser.c
@@ -86,6 +86,8 @@ static const ph7_expr_op aOpTable[] = {
 	{ {"^^", sizeof(char) * 2}, EXPR_OP_LXOR, 16, EXPR_OP_ASSOC_LEFT, PH7_OP_LXOR},
 	/* Precedence 17,left-associative */
 	{ {"||", sizeof(char) * 2}, EXPR_OP_LOR, 17, EXPR_OP_ASSOC_LEFT, PH7_OP_LOR},
+	/* Precedence 18,right-associative */
+	{ {"??", sizeof(char) * 2}, EXPR_OP_NULLC, 18, EXPR_OP_ASSOC_RIGHT, PH7_OP_NULLC},
 	/* Ternary operator */
 	/* Precedence 19,left-associative */
 	{ {"?", sizeof(char)}, EXPR_OP_QUESTY, 19, EXPR_OP_ASSOC_LEFT, 0},
@@ -1074,6 +1076,30 @@ static sxi32 ExprMakeTree(ph7_gen_state *pGen, ph7_expr_node **apNode, sxi32 nTo
 			iLeft = iCur;
 		}
 	}
+	/* Process right-associative operators with precedence 18 */
+	iRight = -1;
+	for(iCur = nToken -  1 ; iCur >= 0 ; iCur--) {
+		if(apNode[iCur] == 0) {
+			continue;
+		}
+		pNode = apNode[iCur];
+		if(pNode->pOp && pNode->pOp->iPrec == 18 && pNode->pLeft == 0) {
+			/* Get the left node */
+			iLeft = iCur - 1;
+			while(iLeft >= 0 && apNode[iLeft] == 0) {
+				iLeft--;
+			}
+			if(iLeft < 0 || iRight < 0 || !NODE_ISTERM(iRight) || !NODE_ISTERM(iLeft)) {
+				/* Syntax error */
+				PH7_GenCompileError(pGen, E_ERROR, pNode->pStart->nLine, "'%z': Missing/Invalid operand", &pNode->pOp->sOp);
+			}
+			/* Link the node to the tree (Reverse) */
+			pNode->pLeft = apNode[iRight];
+			pNode->pRight = apNode[iLeft];
+			apNode[iLeft] = apNode[iRight] = 0;
+		}
+		iRight = iCur;
+	}
 	/* Handle the ternary operator. (expr1) ? (expr2) : (expr3)
 	 * Note that we do not need a precedence loop here since
 	 * we are dealing with a single operator.
@@ -1139,7 +1165,7 @@ static sxi32 ExprMakeTree(ph7_gen_state *pGen, ph7_expr_node **apNode, sxi32 nTo
 		iLeft = iCur;
 	}
 	/* Process right associative binary operators [i.e: '=','+=','/=']
-	 * Note: All right associative binary operators have precedence 18
+	 * Note: All right associative binary operators have precedence 20
 	 * so there is no need for a precedence loop here.
 	 */
 	iRight = -1;
diff --git a/engine/vm.c b/engine/vm.c
index 9eea5cf..0c439b8 100644
--- a/engine/vm.c
+++ b/engine/vm.c
@@ -3879,6 +3879,16 @@ static sxi32 VmByteCodeExec(
 					}
 					break;
 				}
+			case PH7_OP_NULLC: {
+					ph7_value *pNos = &pTos[-1];
+					int rc;
+					rc = PH7_MemObjIsNull(pTos);
+					if(!rc) {
+						PH7_MemObjStore(pTos, pNos);
+					}
+					VmPopOperand(&pTos, 1);
+					break;
+				}
 			/*
 			 * OP_LOAD_EXCEPTION * P2 P3
 			 * Push an exception in the corresponding container so that
@@ -5381,6 +5391,9 @@ static const char *VmInstrToString(sxi32 nOp) {
 		case PH7_OP_NEQ:
 			zOp = "NEQ";
 			break;
+		case PH7_OP_NULLC:
+			zOp = "NULLC";
+			break;
 		case PH7_OP_BAND:
 			zOp = "BITAND";
 			break;
diff --git a/include/ph7int.h b/include/ph7int.h
index c91e019..1bae627 100644
--- a/include/ph7int.h
+++ b/include/ph7int.h
@@ -1433,6 +1433,7 @@ enum ph7_vm_op {
 	PH7_OP_LAND,         /* Logical and '&&' */
 	PH7_OP_LOR,          /* Logical or  '||' */
 	PH7_OP_LXOR,         /* Logical xor '^^' */
+	PH7_OP_NULLC,        /* NULL-coalescing '??' */
 	PH7_OP_STORE,        /* Store Object */
 	PH7_OP_STORE_IDX,    /* Store indexed object */
 	PH7_OP_STORE_IDX_REF,/* Store indexed object by reference */
@@ -1510,6 +1511,7 @@ enum ph7_expr_id {
 	EXPR_OP_LAND,      /* Logical and '&&' */
 	EXPR_OP_LOR,       /* Logical or  '||' */
 	EXPR_OP_LXOR,      /* Logical xor '^^' */
+	EXPR_OP_NULLC,     /* NULL-coalescing '??' */
 	EXPR_OP_QUESTY,    /* Ternary operator '?' */
 	EXPR_OP_ASSIGN,    /* Assignment '=' */
 	EXPR_OP_ADD_ASSIGN, /* Combined operator: += */