Add pipe syntax support for function calls like in Jinja2, resolves #294 (#296)

Author: navrocky

README.md

@@ -270,6 +270,16 @@ render("{{ isArray(guests) }}", data); // "true"
 // Implemented type checks: isArray, isBoolean, isFloat, isInteger, isNumber, isObject, isString,
 ```
 
+The Jinja2 pipe call syntax of functions is also supported:
+
+```.cpp
+// Upper neighbour value
+render("Hello {{ neighbour | upper }}!", data); // "Hello PETER!"
+
+// Sort array and join with comma
+render("{{ [\"B\", \"A\", \"C\"] | sort | join(\",\") }}", data); // "A,B,C"
+```
+
 ### Callbacks
 
 You can create your own and more complex functions with callbacks. These are implemented with `std::function`, so you can for example use C++ lambdas. Inja `Arguments` are a vector of json pointers.

include/inja/lexer.hpp

@@ -115,6 +115,8 @@ class Lexer {
       return make_token(Token::Kind::Comma);
     case ':':
       return make_token(Token::Kind::Colon);
+    case '|':
+      return make_token(Token::Kind::Pipe);
     case '(':
       return make_token(Token::Kind::LeftParen);
     case ')':

include/inja/parser.hpp

@@ -350,6 +350,47 @@ class Parser {
         }
         arguments.emplace_back(expr);
       } break;
+
+      // parse function call pipe syntax
+      case Token::Kind::Pipe: {
+        // get function name
+        get_next_token();
+        if (tok.kind != Token::Kind::Id) {
+          throw_parser_error("expected function name, got '" + tok.describe() + "'");
+        }
+        auto func = std::make_shared<FunctionNode>(tok.text, tok.text.data() - tmpl.content.c_str());
+        // add first parameter as last value from arguments
+        func->number_args += 1;
+        func->arguments.emplace_back(arguments.back());
+        arguments.pop_back();
+        get_peek_token();
+        if (peek_tok.kind == Token::Kind::LeftParen) {
+          get_next_token();
+          // parse additional parameters
+          do {
+            get_next_token();
+            auto expr = parse_expression(tmpl);
+            if (!expr) {
+              break;
+            }
+            func->number_args += 1;
+            func->arguments.emplace_back(expr);
+          } while (tok.kind == Token::Kind::Comma);
+          if (tok.kind != Token::Kind::RightParen) {
+            throw_parser_error("expected right parenthesis, got '" + tok.describe() + "'");
+          }
+        }
+        // search store for defined function with such name and number of args
+        auto function_data = function_storage.find_function(func->name, func->number_args);
+        if (function_data.operation == FunctionStorage::Operation::None) {
+          throw_parser_error("unknown function " + func->name);
+        }
+        func->operation = function_data.operation;
+        if (function_data.operation == FunctionStorage::Operation::Callback) {
+          func->callback = function_data.callback;
+        }
+        arguments.emplace_back(func);
+      } break;
       default:
         goto break_loop;
       }

include/inja/token.hpp

@@ -44,6 +44,7 @@ struct Token {
     GreaterEqual,       // >=
     LessThan,           // <
     LessEqual,          // <=
+    Pipe,               // |
     Unknown,
     Eof,
   };

single_include/inja/inja.hpp

@@ -1002,6 +1002,7 @@ struct Token {
     GreaterEqual,       // >=
     LessThan,           // <
     LessEqual,          // <=
+    Pipe,               // |
     Unknown,
     Eof,
   };
@@ -1138,6 +1139,8 @@ class Lexer {
       return make_token(Token::Kind::Comma);
     case ':':
       return make_token(Token::Kind::Colon);
+    case '|':
+      return make_token(Token::Kind::Pipe);
     case '(':
       return make_token(Token::Kind::LeftParen);
     case ')':
@@ -1797,6 +1800,47 @@ class Parser {
         }
         arguments.emplace_back(expr);
       } break;
+
+      // parse function call pipe syntax
+      case Token::Kind::Pipe: {
+        // get function name
+        get_next_token();
+        if (tok.kind != Token::Kind::Id) {
+          throw_parser_error("expected function name, got '" + tok.describe() + "'");
+        }
+        auto func = std::make_shared<FunctionNode>(tok.text, tok.text.data() - tmpl.content.c_str());
+        // add first parameter as last value from arguments
+        func->number_args += 1;
+        func->arguments.emplace_back(arguments.back());
+        arguments.pop_back();
+        get_peek_token();
+        if (peek_tok.kind == Token::Kind::LeftParen) {
+          get_next_token();
+          // parse additional parameters
+          do {
+            get_next_token();
+            auto expr = parse_expression(tmpl);
+            if (!expr) {
+              break;
+            }
+            func->number_args += 1;
+            func->arguments.emplace_back(expr);
+          } while (tok.kind == Token::Kind::Comma);
+          if (tok.kind != Token::Kind::RightParen) {
+            throw_parser_error("expected right parenthesis, got '" + tok.describe() + "'");
+          }
+        }
+        // search store for defined function with such name and number of args
+        auto function_data = function_storage.find_function(func->name, func->number_args);
+        if (function_data.operation == FunctionStorage::Operation::None) {
+          throw_parser_error("unknown function " + func->name);
+        }
+        func->operation = function_data.operation;
+        if (function_data.operation == FunctionStorage::Operation::Callback) {
+          func->callback = function_data.callback;
+        }
+        arguments.emplace_back(func);
+      } break;
       default:
         goto break_loop;
       }

test/test-renderer.cpp

@@ -154,6 +154,12 @@ Yeah!
                      data) == R""""(Yeah!
 )"""");
   }
+
+  SUBCASE("pipe syntax") {
+    CHECK(env.render("{{ brother.name | upper }}", data) == "CHRIS");
+    CHECK(env.render("{{ brother.name | upper | lower }}", data) == "chris");
+    CHECK(env.render("{{ [\"C\", \"A\", \"B\"] | sort | join(\",\") }}", data) == "A,B,C");
+  }
 }
 
 TEST_CASE("templates") {