Add support for #pragma once directives in shader include files

src/resources/shader-loader.cpp

@@ -24,17 +24,43 @@
 #include "gl/shader-object.hpp"
 #include "gl/shader-program.hpp"
 #include <sstream>
+#include <unordered_set>
+
+/**
+ * Scans a text file for the presence of a `#pragma once` directive.
+ *
+ * @param source Text file to scan.
+ *
+ * @return `true` if the file contains a `#pragma once` directive, `false` otherwise.
+ */
+static bool has_pragma_once(const text_file& source)
+{
+	for (const auto& line: source)
+	{
+		std::istringstream line_stream(line);
+		std::string token;
+		
+		// If line contains a `#pragma once` directive
+		if (line_stream >> token && token == "#pragma" &&
+			line_stream >> token && token == "once")
+		{
+			return true;
+		}
+	}
+	
+	return false;
+}
 
 /**
  * Handles `#pragma include` directives by loading the specified text files and inserting them in place.
  */
-static void handle_includes(text_file* source, resource_manager* resource_manager)
+static void handle_includes(text_file& source, std::unordered_set<const text_file*>& include_once, resource_manager* resource_manager)
 {
 	// For each line in the source
-	for (std::size_t i = 0; i < source->size(); ++i)
+	for (std::size_t i = 0; i < source.size(); ++i)
 	{
 		std::string token;
-		std::istringstream line_stream((*source)[i]);
+		std::istringstream line_stream(source[i]);
 		
 		// If line contains a `#pragma include` directive
 		if (line_stream >> token && token == "#pragma" &&
@@ -49,27 +75,39 @@ static void handle_includes(text_file* source, resource_manager* resource_manage
 				std::string path = token.substr(1, token.length() - 2);
 				
 				// Load include file
-				if (!resource_manager->load<text_file>(path))
+				text_file* include_file = resource_manager->load<text_file>(path);
+				if (!include_file)
 				{
-					(*source)[i] = "#error file not found (" + path + ")";
+					source[i] = "#error file not found (" + path + ")";
 				}
 				else
 				{
-					// Create copy of include file
-					text_file include_file = *(resource_manager->load<text_file>(path));
-					
-					// Handle `#pragma include` directives inside include file
-					handle_includes(&include_file, resource_manager);
-					
-					// Replace #pragma include directive with include file contents
-					source->erase(source->begin() + i);
-					source->insert(source->begin() + i, include_file.begin(), include_file.end());
-					i += include_file.size() - 1;
+					// If file has not been included or has no `#pragma once` directive
+					if (!include_once.contains(include_file))
+					{
+						// If file has `#pragma once` directive
+						if (has_pragma_once(*include_file))
+						{
+							// Add file to set of files to include once
+							include_once.insert(include_file);
+						}
+						
+						// Create a copy of the include file
+						text_file include_file_copy = *include_file;
+						
+						// Handle `#pragma include` directives inside include file
+						handle_includes(include_file_copy, include_once, resource_manager);
+						
+						// Replace #pragma include directive with include file contents
+						source.erase(source.begin() + i);
+						source.insert(source.begin() + i, include_file_copy.begin(), include_file_copy.end());
+						i += include_file_copy.size() - 1;
+					}
 				}
 			}
 			else
 			{
-				(*source)[i] = "#error malformed include directive (" + (*source)[i] + ")";
+				source[i] = "#error malformed include directive (" + source[i] + ")";
 			}
 		}
 	}
@@ -78,15 +116,20 @@ static void handle_includes(text_file* source, resource_manager* resource_manage
 template <>
 gl::shader_program* resource_loader<gl::shader_program>::load(resource_manager* resource_manager, PHYSFS_File* file, const std::filesystem::path& path)
 {
-	// Load shader template source
-	text_file source_lines = *resource_loader<text_file>::load(resource_manager, file, path);
+	// Load shader source file
+	text_file* source_file = resource_loader<text_file>::load(resource_manager, file, path);
+	
+	// Make a copy of the shader source file
+	text_file source_file_copy = *source_file;
 	
 	// Handle `#pragma include` directives
-	handle_includes(&source_lines, resource_manager);
+	std::unordered_set<const text_file*> include_once;
+	include_once.insert(source_file);
+	handle_includes(source_file_copy, include_once, resource_manager);
 	
 	// Join vector of source lines into single string
 	std::ostringstream stream;
-	std::copy(source_lines.begin(), source_lines.end(), std::ostream_iterator<std::string>(stream, "\n"));
+	std::copy(source_file_copy.begin(), source_file_copy.end(), std::ostream_iterator<std::string>(stream, "\n"));
 	
 	// Create shader template
 	render::shader_template* shader = new render::shader_template(stream.str());
@@ -109,15 +152,20 @@ gl::shader_program* resource_loader::load(resource_manager*
 template <>
 render::shader_template* resource_loader<render::shader_template>::load(resource_manager* resource_manager, PHYSFS_File* file, const std::filesystem::path& path)
 {
-	// Load shader template source
-	text_file source_lines = *resource_loader<text_file>::load(resource_manager, file, path);
+	// Load shader template source file
+	text_file* source_file = resource_loader<text_file>::load(resource_manager, file, path);
+	
+	// Make a copy of the shader template source file
+	text_file source_file_copy = *source_file;
 	
 	// Handle `#pragma include` directives
-	handle_includes(&source_lines, resource_manager);
+	std::unordered_set<const text_file*> include_once;
+	include_once.insert(source_file);
+	handle_includes(source_file_copy, include_once, resource_manager);
 	
 	// Join vector of source lines into single string
 	std::ostringstream stream;
-	std::copy(source_lines.begin(), source_lines.end(), std::ostream_iterator<std::string>(stream, "\n"));
+	std::copy(source_file_copy.begin(), source_file_copy.end(), std::ostream_iterator<std::string>(stream, "\n"));
 	
 	// Create shader template
 	render::shader_template* shader = new render::shader_template(stream.str());