Add support for setting subobjects via JSON pointer in set statements. (#202)

E.g. `{% set x.y = 1 %}` sets the `y` member of `x` to 1.

README.md

@@ -198,6 +198,13 @@ Variables can also be defined within the template using the set statment.
 render("{% set new_hour=23 %}{{ new_hour }}pm", data); // "23pm"
 ```
 
+json pointers can be used to set sub-objects:
+```.cpp
+render("{% set time.start=18 %}{{ time.start }}pm", data); // "18pm"
+```
+
+Assignments only set the value within the rendering context; they do not modify the json object passed into the `render` call.
+
 ### Functions
 
 A few functions are implemented within the inja template syntax. They can be called with

include/inja/renderer.hpp

@@ -184,10 +184,10 @@ class Renderer : public NodeVisitor  {
   void visit(const JsonNode& node) {
     if (json_additional_data.contains(node.ptr)) {
       json_eval_stack.push(&(json_additional_data[node.ptr]));
-    
+
     } else if (json_input->contains(node.ptr)) {
       json_eval_stack.push(&(*json_input)[node.ptr]);
-    
+
     } else {
       // Try to evaluate as a no-argument callback
       const auto function_data = function_storage.find_function(node.name, 0);
@@ -662,7 +662,10 @@ class Renderer : public NodeVisitor  {
   }
 
   void visit(const SetStatementNode& node) {
-    json_additional_data[node.key] = *eval_expression_list(node.expression);
+    std::string ptr = node.key;
+    replace_substring(ptr, ".", "/");
+    ptr = "/" + ptr;
+    json_additional_data[nlohmann::json::json_pointer(ptr)] = *eval_expression_list(node.expression);
   }
 
 public:

include/inja/utils.hpp

@@ -69,6 +69,17 @@ inline SourceLocation get_source_location(nonstd::string_view content, size_t po
   return {count_lines + 1, sliced.length() - last_newline};
 }
 
+inline void replace_substring(std::string& s, const std::string& f,
+                              const std::string& t)
+{
+  if (f.empty()) return;
+  for (auto pos = s.find(f);                  // find first occurrence of f
+            pos != std::string::npos;         // make sure f was found
+            s.replace(pos, f.size(), t),      // replace with t, and
+            pos = s.find(f, pos + t.size()))  // find next occurrence of f
+  {}
+}
+
 } // namespace inja
 
 #endif // INCLUDE_INJA_UTILS_HPP_

single_include/inja/inja.hpp

@@ -1907,6 +1907,17 @@ inline SourceLocation get_source_location(nonstd::string_view content, size_t po
   return {count_lines + 1, sliced.length() - last_newline};
 }
 
+inline void replace_substring(std::string& s, const std::string& f,
+                              const std::string& t)
+{
+  if (f.empty()) return;
+  for (auto pos = s.find(f);                  // find first occurrence of f
+            pos != std::string::npos;         // make sure f was found
+            s.replace(pos, f.size(), t),      // replace with t, and
+            pos = s.find(f, pos + t.size()))  // find next occurrence of f
+  {}
+}
+
 } // namespace inja
 
 #endif // INCLUDE_INJA_UTILS_HPP_
@@ -3663,10 +3674,10 @@ class Renderer : public NodeVisitor  {
   void visit(const JsonNode& node) {
     if (json_additional_data.contains(node.ptr)) {
       json_eval_stack.push(&(json_additional_data[node.ptr]));
-    
+
     } else if (json_input->contains(node.ptr)) {
       json_eval_stack.push(&(*json_input)[node.ptr]);
-    
+
     } else {
       // Try to evaluate as a no-argument callback
       const auto function_data = function_storage.find_function(node.name, 0);
@@ -4141,7 +4152,10 @@ class Renderer : public NodeVisitor  {
   }
 
   void visit(const SetStatementNode& node) {
-    json_additional_data[node.key] = *eval_expression_list(node.expression);
+    std::string ptr = node.key;
+    replace_substring(ptr, ".", "/");
+    ptr = "/" + ptr;
+    json_additional_data[nlohmann::json::json_pointer(ptr)] = *eval_expression_list(node.expression);
   }
 
 public:

test/test-renderer.cpp

@@ -125,8 +125,13 @@ TEST_CASE("types") {
   SUBCASE("set statements") {
     CHECK(env.render("{% set predefined=true %}{% if predefined %}a{% endif %}", data) == "a");
     CHECK(env.render("{% set predefined=false %}{% if predefined %}a{% endif %}", data) == "");
-    CHECK_THROWS_WITH(env.render("{% if predefined %}{% endif %}", data), 
+    CHECK(env.render("{% set age=30 %}{{age}}", data) == "30");
+    CHECK(env.render("{% set predefined.value=1 %}{% if existsIn(predefined, \"value\") %}{{predefined.value}}{% endif %}", data) == "1");
+    CHECK(env.render("{% set brother.name=\"Bob\" %}{{brother.name}}", data) == "Bob");
+    CHECK_THROWS_WITH(env.render("{% if predefined %}{% endif %}", data),
                       "[inja.exception.render_error] (at 1:7) variable 'predefined' not found");
+    CHECK(env.render("{{age}}", data) == "29");
+    CHECK(env.render("{{brother.name}}", data) == "Chris");
   }
 
   SUBCASE("short circuit evaluation") {
@@ -210,7 +215,7 @@ TEST_CASE("templates") {
     CHECK(env.render("Test\n   {%- if is_happy %}{{ name }}{% endif %}   ", data) == "Test\nPeter   ");
     CHECK(env.render("   {%+ if is_happy %}{{ name }}{% endif %}", data) == "   Peter");
     CHECK(env.render("   {%- if is_happy %}{{ name }}{% endif -%}   \n   ", data) == "Peter");
-    
+
     CHECK(env.render("   {{- name -}}   \n   ", data) == "Peter");
     CHECK(env.render("Test\n   {{- name }}   ", data) == "Test\nPeter   ");
     CHECK(env.render("   {{ name }}\n ", data) == "   Peter\n ");