Results do not match other implementations

[cburgmer]

The following queries provide results that do not match those of other implementations of JSONPath
(compare https://cburgmer.github.io/json-path-comparison/):

• $.2
  Input:

  {"a": "first", "2": "second", "b": "third"}
  

  Expected output:

  ["second"]
  

  Error:

  Exception in thread "main" org.antlr.v4.runtime.misc.ParseCancellationException
  	at org.antlr.v4.runtime.BailErrorStrategy.recoverInline(BailErrorStrategy.java:66)
  	at org.antlr.v4.runtime.Parser.match(Parser.java:206)
  	at org.jsfr.json.compiler.JsonPathParser.childNode(JsonPathParser.java:672)
  	at org.jsfr.json.compiler.JsonPathParser.relativePath(JsonPathParser.java:272)
  	at org.jsfr.json.compiler.JsonPathParser.path(JsonPathParser.java:159)
  	at org.jsfr.json.compiler.JsonPathCompiler.compile(JsonPathCompiler.java:283)
  	at org.jsfr.json.compiler.JsonPathCompiler.compile(JsonPathCompiler.java:273)
  	at org.jsfr.json.JsonSurfer.collectAll(JsonSurfer.java:262)
  	at query.App.main(App.java:27)
  Caused by: org.antlr.v4.runtime.InputMismatchException
  	at org.antlr.v4.runtime.BailErrorStrategy.recoverInline(BailErrorStrategy.java:61)
  	... 8 more
  

• $[-1]
  Input:

  ["first", "second", "third"]
  

  Expected output:

  ["third"]
  

  Actual output:

  []
  

• $[-1:]
  Input:

  ["first", "second", "third"]
  

  Expected output:

  ["third"]
  

  Actual output:

  ["first", "second", "third"]
  

• $[?(@.key=="some.value")]
  Input:

  [{"key": "some"}, {"key": "value"}, {"key": "some.value"}]
  

  Expected output:

  [{"key": "some.value"}]
  

  Error:

  line 1:11 token recognition error at: '"'
  line 1:22 token recognition error at: '"'
  line 1:12 no viable alternative at input '@.key==some'
  Exception in thread "main" org.antlr.v4.runtime.misc.ParseCancellationException
  	at org.antlr.v4.runtime.BailErrorStrategy.recover(BailErrorStrategy.java:51)
  	at org.jsfr.json.compiler.JsonPathParser.filterExpr(JsonPathParser.java:947)
  	at org.jsfr.json.compiler.JsonPathParser.filter(JsonPathParser.java:768)
  	at org.jsfr.json.compiler.JsonPathParser.relativePath(JsonPathParser.java:307)
  	at org.jsfr.json.compiler.JsonPathParser.path(JsonPathParser.java:159)
  	at org.jsfr.json.compiler.JsonPathCompiler.compile(JsonPathCompiler.java:283)
  	at org.jsfr.json.compiler.JsonPathCompiler.compile(JsonPathCompiler.java:273)
  	at org.jsfr.json.JsonSurfer.collectAll(JsonSurfer.java:262)
  	at query.App.main(App.java:27)
  Caused by: org.antlr.v4.runtime.NoViableAltException
  	at org.antlr.v4.runtime.atn.ParserATNSimulator.noViableAlt(ParserATNSimulator.java:2026)
  	at org.antlr.v4.runtime.atn.ParserATNSimulator.execATN(ParserATNSimulator.java:467)
  	at org.antlr.v4.runtime.atn.ParserATNSimulator.adaptivePredict(ParserATNSimulator.java:393)
  	at org.jsfr.json.compiler.JsonPathParser.filterExpr(JsonPathParser.java:843)
  	... 7 more
  

For reference, the output was generated by the program in https://github.com/cburgmer/json-path-comparison/tree/master/implementations/Java_com.github.jsurfer.

[wanglingsong]

I can try to fix the last case first

[wanglingsong]

Due to the streaming nature of JsonSurfer, Case 2 and 3 with negative step are very hard to implement

[cburgmer]

Just out of curiosity, for a query $[-n] you could keep a window with n entries. When the stream stops you pick the first entry from that window and have your candidate.
The upper memory limit for the window would depend on the size of the entries in the list you are processing. This is very likely no different to what you are currently doing, just n times (= constant) more.

[wanglingsong]

Cool. It does make sense. I will try.

[wanglingsong]

I've just reviewed source code and couldn't figure out a quick fix. So Case 2 & 3 won't be supported in near release