fix issue #20922 by handling missing expr in `exprList` for `tkOf` (#20930)

* fix issue #20922 by handling missing expr in `exprList` for `tkOf`

* fix line numbers in test case

* rewrite exprList requiring expr, add optionalExprList for except

As suggested by @metagn.

* update test case to reflect new code

* update grammar.txt

* update line numbers in test case taking into account nimout

Given the number of errors that are produced it seems easier to do it
this way instead of using `tt.Error`.

1 files changed, 46 insertions, 0 deletions

diff --git a/tests/parser/t20922.nim b/tests/parser/t20922.nim
new file mode 100644
index 000000000..01af9868f
--- /dev/null
+++ b/tests/parser/t20922.nim
@@ -0,0 +1,46 @@
+discard """
+  cmd: "nim check $options --verbosity:0 $file"
+  action: "reject"
+  nimout: '''
+t20922.nim(37, 5) Error: expression expected, but found ':'
+Error: in expression ' '+'': identifier expected, but found ''
+t20922.nim(37, 7) Error: attempting to call undeclared routine: '<Error>'
+Error: in expression ' '+'': identifier expected, but found ''
+t20922.nim(37, 7) Error: attempting to call undeclared routine: '<Error>'
+t20922.nim(37, 7) Error: expression '' cannot be called
+t20922.nim(37, 7) Error: expression '' has no type (or is ambiguous)
+t20922.nim(37, 7) Error: VM problem: dest register is not set
+t20922.nim(45, 7) Error: expression expected, but found ':'
+t20922.nim(46, 5) Error: ':' or '=' expected, but got 'keyword of'
+t20922.nim(45, 9) Error: undeclared identifier: 'x'
+t20922.nim(45, 9) Error: expression 'x' has no type (or is ambiguous)
+Error: in expression ' x': identifier expected, but found ''
+t20922.nim(45, 9) Error: attempting to call undeclared routine: '<Error>'
+Error: in expression ' x': identifier expected, but found ''
+t20922.nim(45, 9) Error: attempting to call undeclared routine: '<Error>'
+t20922.nim(45, 9) Error: expression '' cannot be called
+t20922.nim(45, 9) Error: expression '' has no type (or is ambiguous)
+t20922.nim(45, 9) Error: VM problem: dest register is not set
+t20922.nim(33, 6) Hint: 'mapInstrToToken' is declared but not used [XDeclaredButNotUsed]
+t20922.nim(43, 3) Hint: 'Foo' is declared but not used [XDeclaredButNotUsed]
+'''
+"""
+# original test case issue #20922
+type Token = enum
+  incDataPtr,
+  incDataPtrByte
+
+proc mapInstrToToken(instr: char): Token =
+  case instr:
+  of '>':
+    incDataPtr
+  of: '+':
+    incDataPtrByte
+
+# same issue with `of` in object branches (different parser procs calling `exprList`)
+type
+  Bar = enum A, B
+  Foo = object
+    case kind: Bar
+    of: x: int
+    of B: y: float