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Fix crash with simple string literal if-elif-else template

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp
Domain
tooling

Research direction

Read jinja2cpp/src/template_parser.h, especially the expression and statement closing logic around the shown previous-character checks. Reproduce the reported templates, including literals containing %}, through the existing load and render path. Done means these cases load and render like Python Jinja2 without breaking ordinary statement and expression closing.

Written by the indexing model from the issue text.

Description

The following template loads and renders fine with Python jinja2, but crashes with jinja2cpp.

{% if 'foo' == 'bar'%}
1
{% elif 'foo' == 'foo' %}
2
{% else %}
3
{% endif %}

Note that removing elif, else will instead result in a load error (not a crash).

LOAD ERROR: noname.j2tpl:2:8: error: Expected expression, got: 'foo'
{% if 'foo' == 'bar'%}

Adding a space before '%}' on the first line will make the template actually function correctly.

Ideally, jinja2cpp would be able to handle this template just fine, like Python jinja2.

This looks like it fixes the crash and this example behaves correctly, although it's unclear to me whether this change might introduce other bugs. I noticed there was a similar check during end of expression for "'" (single quote) as well, so I remove that one too.

diff --git a/jinja2cpp/src/template_parser.h b/jinja2cpp/src/template_parser.h
--- a/jinja2cpp/src/template_parser.h
+++ b/jinja2cpp/src/template_parser.h
@@ -466,7 +466,7 @@
                     FinishCurrentLine(match.position() + 2);
                     return MakeParseError(ErrorCode::UnexpectedExprEnd, MakeToken(Token::ExprEnd, { matchStart, matchStart + 2 }));
                 }
-                else if (m_currentBlockInfo.type != TextBlockType::Expression || (*m_template)[match.position() - 1] == '\'')
+                else if (m_currentBlockInfo.type != TextBlockType::Expression)
                     break;

                 m_currentBlockInfo.range.startOffset = FinishCurrentBlock(matchStart, TextBlockType::RawText);
@@ -480,7 +480,7 @@
                     FinishCurrentLine(match.position() + 2);
                     return MakeParseError(ErrorCode::UnexpectedStmtEnd, MakeToken(Token::StmtEnd, { matchStart, matchStart + 2 }));
                 }
-                else if (m_currentBlockInfo.type != TextBlockType::Statement || (*m_template)[match.position() - 1] == '\'')
+                else if (m_currentBlockInfo.type != TextBlockType::Statement)
                     break;

                 m_currentBlockInfo.range.startOffset = FinishCurrentBlock(matchStart, TextBlockType::RawText);

Yeah, looks like string parsing is not handled fully correctly. Things like this appear to work fine in Python jinja2, but don't work in jinja2cpp (regardless of the code change above).

works in jinja2cpp without code change above but fails without
{% if '%}' == '%}' %}
1
{% endif %}

fails in jinja2cpp with or without code change above
{% if 'foo%}' == 'foo%}' %}
2
{% endif %}

It seems that the "check previous char" logic does not fully handle statement closing handling correctly, so removing that logic feels like the right thing to do.

Seems like we need to somehow detect that we are "inside a string literal" and ignore closing statement in such cases.

Dominant language
C++
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Forks
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Avg merge
1h 46m
Merged PRs (30d)
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