Add Jinja support for "indent" string filter (ggml-org#19529)

* Add partial Jinja support for "indent" string filter

* Fully implement indent

* Add tests for all width variants.

* Update tests/test-jinja.cpp

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* Fix getline ignoring trailing newlines

* Update common/jinja/value.cpp

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* fix first indent condition

---------

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

Author: pwilkin

common/jinja/value.cpp

@@ -4,6 +4,7 @@
 // for converting from JSON to jinja values
 #include <nlohmann/json.hpp>
 
+#include <sstream>
 #include <string>
 #include <cctype>
 #include <vector>
@@ -715,8 +716,46 @@ const func_builtins & value_string_t::get_builtins() const {
             return args.get_pos(0);
         }},
         {"tojson", tojson},
-        {"indent", [](const func_args &) -> value {
-            throw not_implemented_exception("String indent builtin not implemented");
+        {"indent", [](const func_args &args) -> value {
+            args.ensure_count(1, 4);
+            value val_input  = args.get_pos(0);
+            value val_width  = args.get_kwarg_or_pos("width", 1);
+            const bool first = args.get_kwarg_or_pos("first", 2)->as_bool(); // undefined == false
+            const bool blank = args.get_kwarg_or_pos("blank", 3)->as_bool(); // undefined == false
+            if (!is_val<value_string>(val_input)) {
+                throw raised_exception("indent() first argument must be a string");
+            }
+            std::string indent;
+            if (is_val<value_int>(val_width)) {
+                indent.assign(val_width->as_int(), ' ');
+            } else if (is_val<value_string>(val_width)) {
+                indent = val_width->as_string().str();
+            } else {
+                indent = "    ";
+            }
+            std::string indented;
+            std::string input = val_input->as_string().str();
+            std::istringstream iss = std::istringstream(input);
+            std::string line;
+            while (std::getline(iss, line)) {
+                if (!indented.empty()) {
+                    indented.push_back('\n');
+                }
+                if ((indented.empty() ? first : (!line.empty() || blank))) {
+                    indented += indent;
+                }
+                indented += line;
+            }
+            if (!input.empty() && input.back() == '\n') {
+                indented.push_back('\n');
+                if (blank) {
+                    indented += indent;
+                }
+            }
+
+            auto res = mk_val<value_string>(indented);
+            res->val_str.mark_input_based_on(val_input->as_string());
+            return res;
         }},
         {"join", [](const func_args &) -> value {
             throw not_implemented_exception("String join builtin not implemented");

tests/test-jinja.cpp

@@ -691,6 +691,48 @@ static void test_filters(testing & t) {
         "{\n  \"a\": 1,\n  \"b\": [\n    1,\n    2\n  ]\n}"
     );
 
+    test_template(t, "indent",
+        "{{ data|indent(2) }}",
+        {{ "data", "foo\nbar" }},
+        "foo\n  bar"
+    );
+
+    test_template(t, "indent first only",
+        "{{ data|indent(width=3,first=true) }}",
+        {{ "data", "foo\nbar" }},
+        "   foo\n   bar"
+    );
+
+    test_template(t, "indent blank lines and first line",
+        "{{ data|indent(width=5,blank=true,first=true) }}",
+        {{ "data", "foo\n\nbar" }},
+        "     foo\n     \n     bar"
+    );
+
+    test_template(t, "indent with default width",
+        "{{ data|indent() }}",
+        {{ "data", "foo\nbar" }},
+        "foo\n    bar"
+    );
+
+    test_template(t, "indent with no newline",
+        "{{ data|indent }}",
+        {{ "data", "foo" }},
+        "foo"
+    );
+
+    test_template(t, "indent with trailing newline",
+        "{{ data|indent(blank=true) }}",
+        {{ "data", "foo\n" }},
+        "foo\n    "
+    );
+
+    test_template(t, "indent with string",
+        "{{ data|indent(width='>>>>') }}",
+        {{ "data", "foo\nbar" }},
+        "foo\n>>>>bar"
+    );
+
     test_template(t, "chained filters",
         "{{ '  HELLO  '|trim|lower }}",
         json::object(),