7 files changed, 42 insertions, 2 deletions
diff --git a/lib/system/chcks.nim b/lib/system/chcks.nim
index 255d97cb2..8c7c95795 100644
--- a/lib/system/chcks.nim
+++ b/lib/system/chcks.nim
@@ -26,8 +26,18 @@ proc raiseIndexError() {.compilerproc, noinline.} =
   sysFatal(IndexDefect, "index out of bounds")
 
 proc raiseFieldError(f: string) {.compilerproc, noinline.} =
+  ## remove after bootstrap > 1.5.1
   sysFatal(FieldDefect, f)
 
+when defined(gcdestructors):
+  proc raiseFieldError2(f: string, discVal: int) {.compilerproc, noinline.} =
+    ## raised when field is inaccessible given runtime value of discriminant
+    sysFatal(FieldError, f & $discVal & "'")
+else:
+  proc raiseFieldError2(f: string, discVal: string) {.compilerproc, noinline.} =
+    ## raised when field is inaccessible given runtime value of discriminant
+    sysFatal(FieldError, formatFieldDefect(f, discVal))
+
 proc raiseRangeErrorI(i, a, b: BiggestInt) {.compilerproc, noinline.} =
   when defined(standalone):
     sysFatal(RangeDefect, "value out of range")
diff --git a/lib/system/indexerrors.nim b/lib/system/indexerrors.nim
index 1b91789bd..6a8cb8a0a 100644
--- a/lib/system/indexerrors.nim
+++ b/lib/system/indexerrors.nim
@@ -1,4 +1,5 @@
 # imported by other modules, unlike helpers.nim which is included
+# xxx this is now included instead of imported, we should import instead
 
 template formatErrorIndexBound*[T](i, a, b: T): string =
   when defined(standalone):
@@ -9,3 +10,6 @@ template formatErrorIndexBound*[T](i, a, b: T): string =
 
 template formatErrorIndexBound*[T](i, n: T): string =
   formatErrorIndexBound(i, 0, n)
+
+template formatFieldDefect*(f, discVal): string =
+  f & discVal & "'"
diff --git a/lib/system/jssys.nim b/lib/system/jssys.nim
index b42dc3a20..63e7b3d9d 100644
--- a/lib/system/jssys.nim
+++ b/lib/system/jssys.nim
@@ -171,8 +171,8 @@ proc raiseRangeError() {.compilerproc, noreturn.} =
 proc raiseIndexError(i, a, b: int) {.compilerproc, noreturn.} =
   raise newException(IndexDefect, formatErrorIndexBound(int(i), int(a), int(b)))
 
-proc raiseFieldError(f: string) {.compilerproc, noreturn.} =
-  raise newException(FieldDefect, f)
+proc raiseFieldError2(f: string, discVal: string) {.compilerproc, noreturn.} =
+  raise newException(FieldDefect, formatFieldDefect(f, discVal))
 
 proc setConstr() {.varargs, asmNoStackFrame, compilerproc.} =
   asm """
diff --git a/lib/system/repr.nim b/lib/system/repr.nim
index 020c2281f..e049d18fa 100644
--- a/lib/system/repr.nim
+++ b/lib/system/repr.nim
@@ -72,6 +72,8 @@ proc reprEnum(e: int, typ: PNimType): string {.compilerRtl.} =
 
   result = $e & " (invalid data!)"
 
+include system/repr_impl
+
 type
   PByteArray = ptr UncheckedArray[byte] # array[0xffff, byte]
 
diff --git a/lib/system/repr_impl.nim b/lib/system/repr_impl.nim
new file mode 100644
index 000000000..b9ec1890f
--- /dev/null
+++ b/lib/system/repr_impl.nim
@@ -0,0 +1,15 @@
+#[
+other APIs common to system/repr and system/reprjs could be refactored here, eg:
+* reprChar
+* reprBool
+* reprStr
+
+Another possibility in future work would be to have a single include file instead
+of system/repr and system/reprjs, and use `when defined(js)` inside it.
+]#
+
+proc reprDiscriminant*(e: int, typ: PNimType): string {.compilerRtl.} =
+  case typ.kind
+  of tyEnum: reprEnum(e, typ)
+  of tyBool: $(e != 0)
+  else: $e
diff --git a/lib/system/repr_v2.nim b/lib/system/repr_v2.nim
index f99f09799..ba94b881d 100644
--- a/lib/system/repr_v2.nim
+++ b/lib/system/repr_v2.nim
@@ -1,3 +1,5 @@
+include system/inclrtl
+
 proc isNamedTuple(T: typedesc): bool {.magic: "TypeTrait".}
   ## imported from typetraits
 
@@ -66,6 +68,11 @@ proc repr*[Enum: enum](x: Enum): string {.magic: "EnumToStr", noSideEffect.}
   ## If a `repr` operator for a concrete enumeration is provided, this is
   ## used instead. (In other words: *Overwriting* is possible.)
 
+proc reprDiscriminant*(e: int): string {.compilerproc.} =
+  # repr and reprjs can use `PNimType` to symbolize `e`; making this work here
+  # would require a way to pass the set of enum stringified values to cgen.
+  $e
+
 proc repr*(p: pointer): string =
   ## repr of pointer as its hexadecimal value
   if p == nil:
diff --git a/lib/system/reprjs.nim b/lib/system/reprjs.nim
index cdc3403f8..28935a4ef 100644
--- a/lib/system/reprjs.nim
+++ b/lib/system/reprjs.nim
@@ -30,6 +30,8 @@ proc reprEnum(e: int, typ: PNimType): string {.compilerRtl.} =
   else:
     result = $e & " (invalid data!)"
 
+include system/repr_impl
+
 proc reprChar(x: char): string {.compilerRtl.} =
   result = "\'"
   case x