String % operand raises a coercion error instead of printf-style formatting #1340

Jinja2 applies printf-style formatting to 'text' % operand. Jinjava parses % as the JUEL modulo operator and coerces the left operand to a number, so a string left operand fails to render.

Affected: master df50b0d7. Releases 2.7.6, 2.8.3 and 2.8.4 behave the same.

Reproduction

{{ 'number'%r }}

Jinja2 renders number. Jinjava raises:

com.hubspot.jinjava.interpret.FatalTemplateErrorsException: Cannot coerce 'number' of class java.lang.String to class java.lang.Double (incompatible value)

Root cause

ExtendedParser maps the % token to AstBinary.MOD (src/main/java/com/hubspot/jinjava/el/ext/ExtendedParser.java:421-424). The JUEL implementation of MOD converts both operands to numbers, and there is no string formatting path for a string left operand.