Fix parser expressions (#2682)

* Fix segmentation faults in amrex::Parser if a constant was not defined.
Without this fix, the following segments of code all seg-fault.
With this fix, each of them will throw an exception instead.
(If the setConstant lines are uncommented, the tests will pass with or without this fix.)

  {
    amrex::Print() << "Attempt 2+a" << std::endl;
    amrex::Parser parser("2+a");
    //parser.setConstant("a", (amrex::Real)3.0);
    const auto parserExec = parser.compile<0>();
    AMREX_ALWAYS_ASSERT(parserExec() == 5);
  }
  {
    amrex::Print() << "Attempt 2-a" << std::endl;
    amrex::Parser parser("2-a");
    //parser.setConstant("a", (amrex::Real)3.0);
    const auto parserExec = parser.compile<0>();
    AMREX_ALWAYS_ASSERT(parserExec() == -1);
  }
  {
    amrex::Print() << "Attempt 2*a" << std::endl;
    amrex::Parser parser("2*a");
    //parser.setConstant("a", (amrex::Real)3.0);
    const auto parserExec = parser.compile<0>();
    AMREX_ALWAYS_ASSERT(parserExec() == 6);
  }
  {
    amrex::Print() << "Attempt 3/a" << std::endl;
    amrex::Parser parser("3/a");
    //parser.setConstant("a", (amrex::Real)3.0);
    const auto parserExec = parser.compile<0>();
    AMREX_ALWAYS_ASSERT(parserExec() == 1);
  }
  {
    amrex::Print() << "Attempt -a" << std::endl;
    amrex::Parser parser("-a");
    //parser.setConstant("a", (amrex::Real)3.0);
    const auto parserExec = parser.compile<0>();
    AMREX_ALWAYS_ASSERT(parserExec() == -3);
  }

Author: philip-blakely

Src/Base/Parser/AMReX_Parser_Exe.cpp

@@ -546,6 +546,10 @@ parser_compile_exe_size (struct parser_node* node, char*& p, std::size_t& exe_si
                 t->i = AMREX_PARSER_LOCAL_IDX0 + lidx;
             } else {
                 t->i = node->rip;
+                if (t->i < 0) {
+                  throw std::runtime_error(std::string("Unknown variable ")
+                                           + ((struct parser_symbol*)node->r)->name);
+                }
             }
             t->v = node->lvp.v;
         }
@@ -564,6 +568,10 @@ parser_compile_exe_size (struct parser_node* node, char*& p, std::size_t& exe_si
                 t->i = AMREX_PARSER_LOCAL_IDX0 + lidx;
             } else {
                 t->i = node->rip;
+                if (t->i < 0) {
+                  throw std::runtime_error(std::string("Unknown variable ")
+                                           + ((struct parser_symbol*)node->r)->name);
+                }
             }
             t->v = node->lvp.v;
         }
@@ -582,6 +590,10 @@ parser_compile_exe_size (struct parser_node* node, char*& p, std::size_t& exe_si
                 t->i = AMREX_PARSER_LOCAL_IDX0 + lidx;
             } else {
                 t->i = node->rip;
+                if (t->i < 0) {
+                  throw std::runtime_error(std::string("Unknown variable ")
+                                           + ((struct parser_symbol*)node->r)->name);
+                }
             }
             t->v = node->lvp.v;
         }
@@ -600,6 +612,10 @@ parser_compile_exe_size (struct parser_node* node, char*& p, std::size_t& exe_si
                 t->i = AMREX_PARSER_LOCAL_IDX0 + lidx;
             } else {
                 t->i = node->rip;
+                if (t->i < 0) {
+                  throw std::runtime_error(std::string("Unknown variable ")
+                                           + ((struct parser_symbol*)node->r)->name);
+                }
             }
             t->v = node->lvp.v;
         }
@@ -710,6 +726,10 @@ parser_compile_exe_size (struct parser_node* node, char*& p, std::size_t& exe_si
                 t->i = AMREX_PARSER_LOCAL_IDX0 + lidx;
             } else {
                 t->i = node->lvp.ip;
+                if (t->i < 0) {
+                  throw std::runtime_error(std::string("Unknown variable ")
+                                           + ((struct parser_symbol*)node->l)->name);
+                }
             }
         }
         exe_size += sizeof(ParserExeNEG_P);