Wrong usage of choice type causes severe bug: "Found error clazz in set of clazzes in the IR even though no earlier errors were reported."

[simonvonhackewitz]

The error message is

error 1: Found error clazz in set of clazzes in the IR even though no earlier errors were reported.  This can only be the result of a severe bug.

one error.

The code causing the error

base32_test is
  my_c : choice String (array u8) is
  mk_choice(x my_c) => x

  # RFC 4618 test vectors
  base32_test_vectors array (tuple my_c String) :=
    [(mk_choice "fo", "MZXQ===="),
     (mk_choice "foo", "MZXW6===")]

  dummy_decode(arr array u8) outcome (array u8) => [0,0,0]

  dec_test =>
    for tup in base32_test_vectors do
      (plain_expected, code) := tup
      out :=
        match dummy_decode code.utf8.as_array
          arr array u8 =>
            plain_actual := String.type.from_bytes arr
            if plain_actual != plain_expected
              error "decoding $code produced '$plain_actual' but should have been '$plain_expected'"
            else
              outcome "ok"
          e error => error "error in test data"
    until !out.ok
      out.err.as_string
    else
      "RFC 4648 test vectors are decoded correctly"
  say dec_test

[fridis]

Reduced the example to reproduce this:

c : choice i32 unit is
a c := 0
_ := 0 != a

with checks, this gives

 > PRECONDITIONS=true POSTCONDITIONS=true ./build/bin/fz ex3362.fz 

error 1: java.lang.Error: ensure-condition failed: AbstractFeature.java:1498 "(this == Types.f_ERROR || ancestor == Types.f_ERROR || Errors.any() || result != null);"
	at dev.flang.util.ANY.ensure(ANY.java:292)
	at dev.flang.ast.AbstractFeature.findInheritanceChain(AbstractFeature.java:1498)
	at dev.flang.air.Clazz.findRedefinition(Clazz.java:1011)
	at dev.flang.air.Clazz.lookup(Clazz.java:1212)
	at dev.flang.air.Clazzes.findClazzes(Clazzes.java:758)
	at dev.flang.air.Clazz$EV.action(Clazz.java:169)
	at dev.flang.ast.Expr.visitExpressions(Expr.java:338)
	at dev.flang.ast.AbstractCall.visitExpressions(AbstractCall.java:99)
	at dev.flang.ast.AbstractAssign.visitExpressions(AbstractAssign.java:139)
	at dev.flang.ast.AbstractBlock.visitExpressions(AbstractBlock.java:99)
	at dev.flang.ast.AbstractFeature.visitExpressions(AbstractFeature.java:1594)
	at dev.flang.air.Clazz.inspectCode(Clazz.java:1528)
	at dev.flang.air.Clazz.findAllClasses(Clazz.java:1572)
	at dev.flang.air.Clazzes.findAllClasses(Clazzes.java:408)
	at dev.flang.fuir.FUIR.<init>(FUIR.java:185)
	at dev.flang.opt.Optimizer.fuir(Optimizer.java:73)
	at dev.flang.tools.Fuzion$Backend.processFrontEnd(Fuzion.java:506)
	at dev.flang.tools.Fuzion.lambda$parseArgsForBackend$3(Fuzion.java:1070)
	at dev.flang.tools.Tool.lambda$run$0(Tool.java:141)
	at dev.flang.util.Errors.runAndExit(Errors.java:957)
	at dev.flang.tools.Tool.run(Tool.java:141)
	at dev.flang.tools.Fuzion.main(Fuzion.java:626)

*** fatal errors encountered, stopping.
one error.