When showing an error, show the instance location

src/V3Ast.cpp

@@ -1083,9 +1083,43 @@ void AstNode::v3errorEndFatal(std::ostringstream& str) const {
     v3errorEnd(str); assert(0); VL_UNREACHABLE
 }
 
+string AstNode::locationStr() const {
+    string str = "... In instance ";
+    const AstNode* backp = this;
+    while (backp) {
+        const AstScope* scopep;
+        if ((scopep = VN_CAST_CONST(backp, Scope))) {
+            // The design is flattened and there are no useful scopes
+            // This is probably because of inilining
+            if (scopep->isTop()) break;
+
+            str += scopep->prettyName();
+            return str;
+        }
+        backp = backp->backp();
+    }
+    backp = this;
+    while (backp) {
+        const AstModule* modp;
+        const AstNodeVarRef* nvrp;
+        if ((modp = VN_CAST_CONST(backp, Module)) && !modp->hierName().empty()) {
+            str += modp->hierName();
+            return str;
+        } else if ((nvrp = VN_CAST_CONST(backp, NodeVarRef))) {
+            string prettyName = nvrp->prettyName();
+            // VarRefs have not been flattened yet and do not contain location information
+            if (prettyName != nvrp->name()) {
+                str += prettyName;
+                return str;
+            }
+        }
+        backp = backp->backp();
+    }
+    return "";
+}
 void AstNode::v3errorEnd(std::ostringstream& str) const {
     if (!m_fileline) {
-        V3Error::v3errorEnd(str);
+        V3Error::v3errorEnd(str, locationStr());
     } else {
         std::ostringstream nsstr;
         nsstr<<str.str();
@@ -1095,7 +1129,7 @@ void AstNode::v3errorEnd(std::ostringstream& str) const {
             const_cast<AstNode*>(this)->dump(nsstr);
             nsstr<<endl;
         }
-        m_fileline->v3errorEnd(nsstr);
+        m_fileline->v3errorEnd(nsstr, locationStr());
     }
 }