From 87d0ae47aa0c0faaeb2a0859f8320795a03d00bd Mon Sep 17 00:00:00 2001
From: aaldevrn <aaldevrn@noreply.org>
Date: Mon, 10 Aug 2026 19:50:20 -0400
Subject: [PATCH] parser: support Python-style implicit string concatenation

Adjacent string literals ("a" "b") are folded into one string ("ab"),
matching Jinja semantics. Some model chat templates (e.g. Gemma-4-E2B) embed
multi-line error messages this way inside raise_exception(...) call args,
which previously failed to parse with 'Expected closing parenthesis in call
args'. Concatenation is only folded between string literals, so operator
expressions and identifiers are unaffected.
---
 include/minja/minja.hpp | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/minja/minja.hpp b/include/minja/minja.hpp
index 5ed0556..583f5bc 100644
--- a/include/minja/minja.hpp
+++ b/include/minja/minja.hpp
@@ -1806,7 +1806,28 @@ class Parser {
       if (it == end) return nullptr;
       if (*it == '"' || *it == '\'') {
         auto str = parseString();
-        if (str) return std::make_shared<Value>(*str);
+        if (str) {
+          // Python-style implicit string concatenation: adjacent string
+          // literals ("a" "b") fold into one ("ab"). Jinja (and the Gemini/
+          // Gemma templates that embed tool-call error messages) relies on it;
+          // Minja's parser rejected the multi-line call-arg form.
+          while (it != end) {
+            auto save = it;
+            consumeSpaces();
+            if (it != end && (*it == '"' || *it == '\'')) {
+              auto next = parseString();
+              if (!next) {
+                it = save;
+                break;
+              }
+              *str += *next;
+            } else {
+              it = save;
+              break;
+            }
+          }
+          return std::make_shared<Value>(*str);
+        }
       }
       static std::regex prim_tok(R"(true\b|True\b|false\b|False\b|None\b)");
       auto token = consumeToken(prim_tok);