ParmParse: Line Continuation

In #3433, we added an option to disable multi-line support to avoid certain
types of errors. Since multi-line support seems to be desirable feature, we
add a new feature that uses `\` as line continuation. To avoid confusion, we
have decided to stop supporting the old style of multi-line values and make
it a runtime error. Hopefully it does not cause too much trouble for users.

Src/Base/AMReX_ParmParse.H

@@ -32,18 +32,24 @@ class IntVect;
 //
 // Comments in an input file include all text from a '#' character to the
 // end of the line.  Here is an example input file:
-//
-//   niter = 100                # niter is an integer
-//   title = "Double Wammy"     # example of a string with spaces
-//   cell_size = 0.5 0.75       # cell spacing in each dimension
-//   plot.var = Density 1 10    # a list of values
-//   plot.var = Energy  5 12    # another list of values
-//   bigarray = 1 2 3 4 5 6 7 8 # first part of array
-//              9 10 11 12      # continuation of bigarray
-//   test = apple "boy blue" 10 20 30 40
-//   FILE = prob_file           # insert contents of this "prob_file" here
-//
-// The "FILE = <filename>" definition is special.  Rather than just
+/*
+   niter = 100                # niter is an integer
+   title = "Double Wammy"     # example of a string with spaces
+   cell_size = 0.5 0.75       # cell spacing in each dimension
+   plot.var = Density 1 10    # a list of values
+   plot.var = Energy  5 12    # another list of values
+   bigarray = 1 2 3 4 5 6 7 8 \
+              9 10 11 12      # continuation of bigarray
+   multi_line_string = "This is a
+                        multi-line string."
+   test = apple "boy blue" 10 20 30 40
+   FILE = prob_file           # insert contents of this "prob_file" here
+*/
+// For values spanning multiple lines, one must use '\' at the end of a line
+// for continuation, otherwise it's a runtime error. Note that there must be
+// at least one space before the continuation character `\`.  Multiple lines
+// inside a pair of double quotes are considered a single string containing
+// '\n's. The "FILE = <filename>" definition is special.  Rather than just
 // adding this entry to the database, it reads the contents of <filename>
 // into the database.
 //
@@ -229,10 +235,12 @@ class IntVect;
 *
 *     plot.var = Energy  5 12
 *
-*     bigarray = 1 2 3 4 5 6 7 8
-*
+*     bigarray = 1 2 3 4 5 6 7 8 \
 *                9 10 11 12
 *
+*     multi_line_string = "This is a
+*                          multi-line string."
+*
 *     aBox    = ((0,0) (5,5))
 *
 *     test = apple "boy blue" 10 20 30 40
@@ -1052,37 +1060,6 @@ public:
     //! Returns [prefix.]* parameters.
     [[nodiscard]] static std::set<std::string> getEntries (const std::string& prefix = std::string());
 
-    /**
-     * \brief Control multi-line support
-     *
-     * By default, ParmParse supports multi-line values. For example,
-     \verbatim
-         plot_vars = dens vx vy vx
-                     energy entropy
-     \endverbatim
-     * This can be disabled by calling this function setMultiLineSupport(false)
-     * before amrex::Initialize(). This can avoid errors in inputs like,
-     \verbatim
-         algo.current_deposition = direct
-
-         # Enable galilean
-         psatd.use_default_v_galilean # Unfortunately we forgot = 1
-     \endverbatim
-     * With multi-line support, this is equivalent to
-     \verbatim
-         algo.current_deposition = direct psatd.use_default_v_galilean
-     \endverbatim
-     * With multi-line support disabled, it will abort. Note that after
-     * multi-line support is disabled, one is still allowed to have
-     \verbatim
-         f = "x + y
-              + sin(z)"
-     \endverbatim
-     * because here what's inside the pair of double quotes is considered a
-     * single string.
-     */
-    static void setMultiLineSupport (bool b);
-
     struct PP_entry;
     using Table = std::list<PP_entry>;
     static void appendTable(ParmParse::Table& tab);

Src/Base/AMReX_ParmParse.cpp

@@ -34,17 +34,8 @@ static bool finalize_verbose = false;
 static bool finalize_verbose = true;
 #endif
 
-namespace {
-    bool g_multi_line_support = true;
-}
-
 std::string const ParmParse::FileKeyword = "FILE";
 
-void ParmParse::setMultiLineSupport (bool b)
-{
-    g_multi_line_support = b;
-}
-
 //
 // Used by constructor to build table.
 //
@@ -287,6 +278,21 @@ eat_garbage (const char*& str)
             if (*str == '\n') { ++num_linefeeds; }
             str++;
         }
+        else if ( *str == '\\' ) // '\' followed by a line break is continuation to next line
+        {
+            // Unfortunately, a line break has three variants, \r, \n, and \r\n.
+            if (*(str+1) == '\n') {
+                str += 2;
+            } else if (*(str+1) == '\r') {
+                if (*(str+2) == '\n') {
+                    str += 3;
+                } else {
+                    str += 2;
+                }
+            } else {
+                break;
+            }
+        }
         else
         {
             break;
@@ -703,14 +709,14 @@ bldTable (const char*&                    str,
             }
             AMREX_FALLTHROUGH;
         case pEOF:
-            if (! g_multi_line_support &&
-                std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
+            if (std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
             {
                 std::string error_message("ParmParse: Multiple lines in ");
                 error_message.append(cur_name).append(" =");
                 for (auto const& x : cur_list) {
                     error_message.append(" ").append(x);
                 }
+                error_message.append(". Must use \\ for line continuation.");
                 amrex::Abort(error_message);
             }
             addDefn(cur_name,cur_list,tab);
@@ -725,14 +731,14 @@ bldTable (const char*&                    str,
                 tmp_str = cur_list.back();
                 cur_list.pop_back();
                 cur_linefeeds.pop_back();
-                if (! g_multi_line_support &&
-                    std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
+                if (std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
                 {
                     std::string error_message("ParmParse: Multiple lines in ");
                     error_message.append(cur_name).append(" =");
                     for (auto const& x : cur_list) {
                         error_message.append(" ").append(x);
                     }
+                    error_message.append(". Must use \\ for line continuation.");
                     amrex::Abort(error_message);
                 }
                 addDefn(cur_name, cur_list, tab);
@@ -754,14 +760,14 @@ bldTable (const char*&                    str,
                 tmp_str = cur_list.back();
                 cur_list.pop_back();
                 cur_linefeeds.pop_back();
-                if (! g_multi_line_support &&
-                    std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
+                if (std::accumulate(cur_linefeeds.begin(), cur_linefeeds.end(), int(0)) > 0)
                 {
                     std::string error_message("ParmParse: Multiple lines in ");
                     error_message.append(cur_name).append(" =");
                     for (auto const& x : cur_list) {
                         error_message.append(" ").append(x);
                     }
+                    error_message.append(". Must use \\ for line continuation.");
                     amrex::Abort(error_message);
                 }
                 addDefn(cur_name,cur_list,tab);