typespec1-5  Exercise 3: Five Decorator Mistakes
=====================================================

broken5.tsp:

  namespace Broken5;

  model Item {
    @maxLength(10) count: int32;
    @minValue("one") qty: int32;
    @minItems(3) @maxItems(1) tags: string[];
    @pattern(7) code: string;
    @visibility(Lifecycle.Created) note: string;
  }

PREDICTION (from the signatures: minLength/maxLength target a string or property; maxValue's argument is a number; minItems and maxItems take integers; pattern's argument is a string)
  line 4  @maxLength(10) on an int32     -> decorator-wrong-target (the target must be a string)
  line 5  @minValue("one")               -> invalid-argument: a string is not a number
  line 6  @minItems(3) @maxItems(1)      -> invalid-range: 3..1
  line 7  @pattern(7)                    -> invalid-argument: a number is not a string
  line 8  Lifecycle.Created              -> invalid-ref: the enum has no member 'Created' (the phases are Create, Read, Update, and others I did not list)

Compiler output:

  TypeSpec compiler v1.17.0

  - Compiling...
  × Compiling
  Diagnostics were reported during compilation:

  ex/broken5.tsp:4:3 - error decorator-wrong-target: Cannot apply @maxLength decorator to type it is not a string
  > 4 |   @maxLength(10) count: int32;
      |    ^^^^^^^^^^^^^^
  ex/broken5.tsp:5:13 - error invalid-argument: Argument of type '"one"' is not assignable to parameter of type 'valueof numeric | utcDateTime | offsetDateTime | plainDate | plainTime | duration'
  > 5 |   @minValue("one") qty: int32;
      |              ^^^^^
  ex/broken5.tsp:6:3 - error invalid-range: Range "3..1" is invalid.
  > 6 |   @minItems(3) @maxItems(1) tags: string[];
      |    ^^^^^^^^^^^^
  ex/broken5.tsp:7:12 - error invalid-argument: Argument of type '7' is not assignable to parameter of type 'valueof string'
  > 7 |   @pattern(7) code: string;
      |             ^
  ex/broken5.tsp:8:25 - error invalid-ref: Enum doesn't have member Created
  > 8 |   @visibility(Lifecycle.Created) note: string;
      |                          ^^^^^^^

  Found 5 errors.

fixed5.tsp (compiles with no errors):

  namespace Fixed5;

  model Item {
    @maxValue(10) count: int32;
    @minValue(1) qty: int32;
    @minItems(1) @maxItems(3) tags: string[];
    @pattern("^[A-Z]+$") code: string;
    @visibility(Lifecycle.Create) note: string;
  }

PREDICTION CHECK
  All five predicted, with the right line and the right error code. The one I did not predict exactly was which column the range error points to (it points to the @minItems decorator: the range is the pair of values taken together).
THE FIXES
  count: @maxValue(10), because the number needs a number rule. qty: @minValue(1). tags: the range written the right way round, (1, 3). code: a string pattern. note: Lifecycle.Create.

WHY THIS WORKS AS AN ANSWER
---------------------------
The compiler reports all five in one run because they are independent. Every message can be predicted from the decorator's signature, which is in the library's own .tsp files: reading the signature first is faster than reading the message afterwards.