Fix handling of \\" sequences in literals, closes #813

And clean up a couple of stray `#line` directives we shouldn't add in a Cpp1-only source file that were added in the earlier commit today, this restores the `passthrough-tests` to passing with zero diffs

Author: hsutter

regression-tests/test-results/mixed-allcpp1-hello.cpp

@@ -1,5 +1,3 @@
-#line 1 "mixed-allcpp1-hello.cpp2"
-#line 1 "mixed-allcpp1-hello.cpp2"
 
 //  Step 1: rename .cpp to .cpp2
 

regression-tests/test-results/mixed-intro-example-three-loops.cpp

@@ -1,5 +1,3 @@
-#line 1 "mixed-intro-example-three-loops.cpp2"
-#line 1 "mixed-intro-example-three-loops.cpp2"
 #include <iostream>
 #include <iomanip>
 #include <vector>

source/io.h

@@ -578,6 +578,7 @@ auto process_cpp_line(
     struct process_line_ret r { in_comment, true , in_raw_string_literal};
 
     auto prev = ' ';
+    auto prev2 = ' ';
     for (auto i = colno_t{0}; i < ssize(line); ++i)
     {
         //  Local helper functions for readability
@@ -640,7 +641,7 @@ auto process_cpp_line(
                     //  If this isn't an escaped quote, toggle string literal state
                     if (
                         !in_comment
-                        && prev != '\\'
+                        && (prev != '\\' || prev2 == '\\')
                         && (in_string_literal || prev != '\'')
                         && !in_raw_string_literal
                         )
@@ -683,6 +684,7 @@ auto process_cpp_line(
             }
         }
 
+        prev2 = prev;
         prev = line[i];
     }
 
@@ -714,6 +716,7 @@ auto process_cpp2_line(
     auto found_end = false;
 
     auto prev = ' ';
+    auto prev2 = ' ';
     auto in_string_literal = false;
     auto in_char_literal   = false;
 
@@ -729,14 +732,14 @@ auto process_cpp2_line(
         else if (in_string_literal)
         {
             switch (line[i]) {
-            break;case '"': if (prev != '\\') { in_string_literal = false; }
+            break;case '"': if (prev != '\\' || prev2 == '\\') { in_string_literal = false; }
             break;default: ;
             }
         }
         else if (in_char_literal)
         {
             switch (line[i]) {
-            break;case '\'': if (prev != '\\') { in_char_literal = false; }
+            break;case '\'': if (prev != '\\' || prev2 == '\\') { in_char_literal = false; }
             break;default: ;
             }
         }
@@ -776,15 +779,16 @@ auto process_cpp2_line(
                 if (prev == '/') { in_comment = false; return found_end; }
 
             break;case '"':
-                if (prev != '\\') { in_string_literal = true; }
+                if (prev != '\\' || prev2 == '\\') { in_string_literal = true; }
 
             break;case '\'':
-                if (prev != '\\') { in_char_literal = true; }
+                if (prev != '\\' || prev2 == '\\') { in_char_literal = true; }
 
             break;default: ;
             }
         }
 
+        prev2 = prev;
         prev = line[i];
     }
 

source/to_cpp1.h

@@ -1315,7 +1315,13 @@ class cppfront
             printer.print_extra( "\n#include \"cpp2util.h\"\n\n" );
         }
 
-        printer.reset_line_to(1, true);
+        if (
+            source.has_cpp2()
+            && !flag_clean_cpp1
+            )
+        {
+            printer.reset_line_to(1, true);
+        }
 
         for (auto& section : tokens.get_map())
         {
@@ -1342,10 +1348,9 @@ class cppfront
             )
         {
             printer.print_extra( "\n//=== Cpp2 type definitions and function declarations ===========================\n\n" );
+            printer.reset_line_to(1, true);
         }
 
-        printer.reset_line_to(1, true);
-
         assert (printer.get_phase() == positional_printer::phase1_type_defs_func_decls);
         for (
             lineno_t curr_lineno = 0;
@@ -1485,12 +1490,15 @@ class cppfront
         printer.finalize_phase();
         printer.next_phase();
 
-        if (!flag_clean_cpp1) {
+        if (
+            source.has_cpp2()
+            && !flag_clean_cpp1
+            )
+        {
             printer.print_extra( "\n//=== Cpp2 function definitions =================================================\n\n" );
+            printer.reset_line_to(1, true);
         }
 
-        printer.reset_line_to(1, true);
-
         for (auto& section : tokens.get_map())
         {
             assert (!section.second.empty());