Verilog: fix includes of files in same subdirectory

This fixes the case where a Verilog file is in a subdirectory and a local
include is in the same subdirectory.

Author: kroening

regression/verilog/preprocessor/in_subdir.desc

@@ -1,7 +1,7 @@
-KNOWNBUG
+CORE
 subdir/in_subdir.v
 --preprocess
+`line 1 "subdir/include_file\.vh" 1
 ^EXIT=0$
 ^SIGNAL=0$
 --
-include file in subdirectory not found

regression/verilog/preprocessor/include2.desc

@@ -4,7 +4,7 @@ include2.v
 // Enable multi-line checking
 activate-multi-line-match
 `line 1 "include2\.v" 0
-`line 1 "include_file\.vh" 1
+`line 1 "subdir/include_file\.vh" 1
 
 `line 2 "include2\.v" 2
 ^EXIT=0$

src/verilog/verilog_preprocessor.cpp

@@ -98,23 +98,29 @@ Function: verilog_preprocessort::include
 
 \*******************************************************************/
 
-std::string
-verilog_preprocessort::find_include_file(const std::string &filename)
+std::string verilog_preprocessort::find_include_file(
+  const std::string &including_file,
+  const std::string &given_filename)
 {
-  // first try filename as is
-  if(std::filesystem::directory_entry(filename).exists())
-    return filename; // done
+  {
+    // First try given filename relative to the path of the
+    // including file.
+    auto path = std::filesystem::path(including_file);
+    path.replace_filename(given_filename);
+    if(std::filesystem::directory_entry(path).exists())
+      return path; // done
+  }
 
   // try include paths in given order
   for(const auto &path : config.verilog.include_paths)
   {
-    auto full_name = std::filesystem::path(path).append(filename);
+    auto full_name = std::filesystem::path(path).append(given_filename);
     if(std::filesystem::directory_entry(full_name).exists())
       return full_name; // done
   }
 
   throw verilog_preprocessor_errort()
-    << "include file `" << filename << "' not found";
+    << "include file `" << given_filename << "' not found";
 }
 
 /*******************************************************************\
@@ -507,8 +513,8 @@ void verilog_preprocessort::directive()
         << "expecting a string literal after `include";
 
     // strip quotes off string literal, escaping, etc.
-    auto filename = file_token.string_literal_value();
-    auto full_path = find_include_file(filename);
+    auto given_filename = file_token.string_literal_value();
+    auto full_path = find_include_file(context().filename, given_filename);
 
 #ifdef _MSC_VER
     auto in = new std::ifstream(widen(full_path));
@@ -522,7 +528,7 @@ void verilog_preprocessort::directive()
     tokenizer().skip_until_eol();
     tokenizer().next_token(); // eat the \n
 
-    context_stack.emplace_back(true, in, filename);
+    context_stack.emplace_back(true, in, full_path);
     emit_line_directive(1); // 'enter'
     // we now continue in the new context
   }

src/verilog/verilog_preprocessor.h

@@ -44,7 +44,9 @@ class verilog_preprocessort:public preprocessort
   definest defines;
 
   void directive();
-  std::string find_include_file(const std::string &filename);
+  std::string find_include_file(
+    const std::string &including_file,
+    const std::string &given_filename);
   definet::parameterst parse_define_parameters();
 
   using define_argumentst = std::map<std::string, std::vector<tokent>>;