`cel-go` inherits RFC 3339 parsing bugs from Golang's `time.Parse()`

[hudlow]

Describe the bug
cel-go inherits RFC 3339 parsing bugs from Golang's time.Parse()

To Reproduce
Check which components this affects:

• parser
• checker
• interpreter

Sample expression and input that reproduces the issue:

(
  timestamp("2025-01-17T01:00:00.001Z") ==
  timestamp("2025-01-17T01:00:00,001Z") // comma-delimited fractional seconds
) &&
(
  timestamp("2025-01-17T01:00:00Z") ==
  timestamp("2025-01-17T1:00:00Z") // single-digit hour
) &&
(
  timestamp("2025-01-17T01:01:01.001+00:01") ==
  timestamp("2025-01-18T01:01:01.001+24:01") // offset > 24:00
) &&
(
  timestamp("2025-01-17T01:01:01.001+01:00") ==
  timestamp("2025-01-17T01:01:01.001+00:60") // offset minute > 59
)

Test setup:

package main

import (
  "fmt"
  "github.com/google/cel-go/cel"
)

func main() {
  env, _ := cel.NewEnv()
  ast, _ := env.Compile(`
    (
      timestamp("2025-01-17T01:00:00.001Z") ==
      timestamp("2025-01-17T01:00:00,001Z") // comma-delimited fractional seconds
    ) &&
    (
      timestamp("2025-01-17T01:00:00Z") ==
      timestamp("2025-01-17T1:00:00Z") // single-digit hour
    ) &&
    (
      timestamp("2025-01-17T01:01:01.001+00:01") ==
      timestamp("2025-01-18T01:01:01.001+24:01") // offset > 24:00
    ) &&
    (
      timestamp("2025-01-17T01:01:01.001+01:00") ==
      timestamp("2025-01-17T01:01:01.001+00:60") // offset minute > 59
    )
  `)
  prg, _ := env.Program(ast)
  out, _, _ := prg.Eval(map[string]any{})

  fmt.Println(out)
}

Expected behavior
Each of the latter examples should result in an error from the timestamp() function

Additional context
If compatibility is needed, I recommend we add an option in cel-go to provide compatibility rather than forcing other implementations to replicate Golang's bugs.

[TristonianJones]

Thanks, this is a good suggestion. I'm a little surprised that Golang has these bugs, but it's useful to know they're there.