[PYTHON] Cannot build client with custom README.mustache template

Description

Python client is not being built when using default README.mustache as a custom template.

Swagger-codegen version

3.0.25

Swagger declaration file content or url

https://github.com/OAI/OpenAPI-Specification/blob/main/examples/v3.0/petstore.yaml

Command line used for generation

java -jar swagger-codegen-cli.jar generate -i petstore.yaml -l python --template-dir /tmp/custom_tpl  -o /tmp/client

Steps to reproduce

When running without -t --template-dir switch it works as expected.
When I simply copy swagger-codegen/modules/swagger-codegen/src/main/resources/python/README.mustache file into a folder and provide it using -t it throws an exception

cp ~/Code/swagger-codegen/modules/swagger-codegen/src/main/resources/python/README.mustache /tmp/custom_tpl
java -jar swagger-codegen-cli.jar generate -i petstore.yaml -l python --template-dir /tmp/custom_tpl  -o /tmp/client

Exception in thread "Thread-0" java.lang.RuntimeException: Could not generate supporting file 'SupportingFile:
    templateFile: README.mustache
    folder:
    destinationFilename: README.md
'
    at io.swagger.codegen.v3.DefaultGenerator.generateSupportingFiles(DefaultGenerator.java:663)
    at io.swagger.codegen.v3.DefaultGenerator.generate(DefaultGenerator.java:786)
    at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:378)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: com.github.jknack.handlebars.HandlebarsException: /tmp/custom_tpl/README.mustache:61:24: found: '-first', expected: 'id'
{{#apiInfo}}{{#apis}}{{#-first}}{{#operations}}{{#operation}}{{#-first}}{{#hasAuthMethods}}{{#authMethods}}{{#isBasic}}
                        ^
    at com.github.jknack.handlebars.internal.HbsErrorReporter.syntaxError(HbsErrorReporter.java:93)
    at com.github.jknack.handlebars.internal.antlr.ProxyErrorListener.syntaxError(ProxyErrorListener.java:41)
    at com.github.jknack.handlebars.internal.antlr.Parser.notifyErrorListeners(Parser.java:544)
    at com.github.jknack.handlebars.internal.HbsErrorStrategy.reportInputMismatch(HbsErrorStrategy.java:186)
    at com.github.jknack.handlebars.internal.antlr.DefaultErrorStrategy.reportError(DefaultErrorStrategy.java:139)
    at com.github.jknack.handlebars.internal.HbsParser.sexpr(HbsParser.java:922)
    at com.github.jknack.handlebars.internal.HbsParser.block(HbsParser.java:659)
    at com.github.jknack.handlebars.internal.HbsParser.statement(HbsParser.java:337)
    at com.github.jknack.handlebars.internal.HbsParser.body(HbsParser.java:222)
    at com.github.jknack.handlebars.internal.HbsParser.block(HbsParser.java:673)
    at com.github.jknack.handlebars.internal.HbsParser.statement(HbsParser.java:337)
    at com.github.jknack.handlebars.internal.HbsParser.body(HbsParser.java:222)
    at com.github.jknack.handlebars.internal.HbsParser.block(HbsParser.java:673)
    at com.github.jknack.handlebars.internal.HbsParser.statement(HbsParser.java:337)
    at com.github.jknack.handlebars.internal.HbsParser.body(HbsParser.java:222)
    at com.github.jknack.handlebars.internal.HbsParser.template(HbsParser.java:165)
    at com.github.jknack.handlebars.internal.HbsParserFactory$1.parse(HbsParserFactory.java:86)
    at com.github.jknack.handlebars.cache.NullTemplateCache.get(NullTemplateCache.java:54)
    at com.github.jknack.handlebars.Handlebars.compile(Handlebars.java:513)
    at com.github.jknack.handlebars.Handlebars.compile(Handlebars.java:438)
    at com.github.jknack.handlebars.Handlebars.compile(Handlebars.java:419)
    at io.swagger.codegen.v3.templates.HandlebarTemplateEngine.getHandlebars(HandlebarTemplateEngine.java:52)
    at io.swagger.codegen.v3.templates.HandlebarTemplateEngine.getRendered(HandlebarTemplateEngine.java:25)
    at io.swagger.codegen.v3.DefaultGenerator.generateSupportingFiles(DefaultGenerator.java:634)

It's worth noticing that the exception comes from handlebars generator, not mustache.
When I explicitly set the template engine to mustache, a different exception is being thrown:

java -jar swagger-codegen-cli.jar generate -i petstore.yaml -l python --template-engine 'mustache' --template-dir /tmp/custom_tpl  -o /tmp/

Exception in thread "Thread-0" java.lang.RuntimeException: Could not generate model 'Error'
    at io.swagger.codegen.v3.DefaultGenerator.generateModels(DefaultGenerator.java:451)
    at io.swagger.codegen.v3.DefaultGenerator.generate(DefaultGenerator.java:779)
    at io.swagger.codegen.v3.cli.cmd.Generate.run(Generate.java:378)
    at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: com.samskivert.mustache.MustacheParseException: Section close tag with mismatched open tag 'each' != 'each discriminator.mapping' @ line 62
    at com.samskivert.mustache.Mustache$Accumulator.requireSameName(Mustache.java:671)
    at com.samskivert.mustache.Mustache$Accumulator$1.addCloseSectionSegment(Mustache.java:603)
    at com.samskivert.mustache.Mustache$Accumulator.addTagSegment(Mustache.java:629)
    at com.samskivert.mustache.Mustache$Parser.parseChar(Mustache.java:498)
    at com.samskivert.mustache.Mustache$Parser.parse(Mustache.java:396)
    at com.samskivert.mustache.Mustache.compile(Mustache.java:314)
    at com.samskivert.mustache.Mustache$Compiler.compile(Mustache.java:87)
    at com.samskivert.mustache.Mustache$Compiler.compile(Mustache.java:82)
    at io.swagger.codegen.v3.templates.MustacheTemplateEngine.getRendered(MustacheTemplateEngine.java:43)
    at io.swagger.codegen.v3.DefaultGenerator.processTemplateToFile(DefaultGenerator.java:795)
    at io.swagger.codegen.v3.DefaultGenerator.generateModels(DefaultGenerator.java:438)

Reproduce the report with petstore.yaml, the Python generator, and the copied README.mustache template, then inspect DefaultGenerator and the HandlebarTemplateEngine and MustacheTemplateEngine paths shown in the stack traces. Done means a custom copy of the Python README.mustache generates the client successfully with the reported command and template engine behavior is consistent.