many bugfixes for js (#14158)

* many bugfixes for js

fixes #12672, fixes #14153, closes #14123, closes #11331, fixes #11783, fixes #13966, fixes #14087, fixes #14117, closes #12256.

mostly fixes the fact that it was allowed to assign to newly created temp variables. additionally attempts to get rid of null initialized seqs/strings (though they might pop up here and there); this simplifies a lot of things and makes code size smaller. even if null seqs/strings pop up here and there it's still better than all those bugs existing.

* formatting fixes

* CI fixes

* more CI fixes

tests/js/t12672.nim

@@ -0,0 +1,12 @@
+discard """
+  output: ""
+"""
+
+proc foo =
+  var x: seq[seq[int]]
+  for row in x.mitems:
+    let i = 1
+    echo row
+    inc row[i-1]
+
+foo()

tests/js/t14153.nim

@@ -0,0 +1,22 @@
+discard """
+  output: '''
+index 5 not in 0 .. 2
+index 5 not in 0 .. 2
+'''
+"""
+
+var x = @[1, 2, 3]
+
+try:
+  echo x[5]
+except IndexError:
+  echo getCurrentExceptionMsg()
+except:
+  doAssert false
+
+try:
+  x[5] = 8
+except IndexError:
+  echo getCurrentExceptionMsg()
+except:
+  doAssert false

tests/js/tjshello.nim

@@ -1,4 +1,5 @@
 discard """
+  cmd: "nim $target $options --stackTrace:off --lineTrace:off $file"
   output: "Hello World"
   maxcodesize: 1000
   ccodecheck: "!@'function'"
@@ -7,4 +8,3 @@ discard """
 import jsconsole
 
 console.log "Hello World"
-

tests/js/tjshello_stacktrace.nim

@@ -0,0 +1,9 @@
+discard """
+  output: "Hello World"
+  maxcodesize: 4500
+  ccodecheck: "!@'function'"
+"""
+
+import jsconsole
+
+console.log "Hello World"

tests/js/tmangle.nim

@@ -62,8 +62,8 @@ block:
     result = result and obj1.`&&`.addr[] == "bar".cstring
     result = result and obj2.`if` == 0
     result = result and obj2.`for` == 0
-    result = result and obj2.`==`.isNil()
-    result = result and obj2.`&&`.isNil()
+    result = result and obj2.`==`.len == 0
+    result = result and obj2.`&&`.len == 0
   echo test()
 
 # Test codegen for fields with uppercase letters:

tests/js/trepr.nim

@@ -308,21 +308,21 @@ b = 0,
 c = 0.0,
 d = '\0',
 e = eA,
-f = nil,
+f = "",
 g = {},
 h = {},
-i = [nil, nil, nil],
-j = nil,
+i = ["", "", ""],
+j = @[],
 k = 0,
-l = [a = nil,
-b = nil],
+l = [a = "",
+b = @[]],
 m = nil,
 n = nil,
-o = [Field0 = [a = nil,
-b = nil],
-Field1 = nil],
+o = [Field0 = [a = "",
+b = @[]],
+Field1 = ""],
 p = nil,
-q = nil]
+q = ""]
 """)
   doAssert(repr(cc) == """
 [a = 12,

tests/js/ttempgen.nim

@@ -0,0 +1,79 @@
+discard """
+  output: '''
+foo
+'''
+"""
+
+block: # #12672
+  var a = @[1]
+  let i = 1
+  inc a[i-1]
+
+  var b: seq[int]
+  doAssertRaises(IndexDefect): inc b[0]
+  doAssertRaises(IndexDefect): inc b[i-1]
+
+  var x: seq[seq[int]]
+  doAssertRaises(IndexDefect): # not TypeError
+    inc x[0][i-1]
+
+block: # #14087
+  type Obj = object
+    str: string
+
+  var s = @[Obj(str: "abc"), Obj(str: "def")]
+  s[1].str.add("ghi")
+  s[s.len - 1].str.add("jkl")
+  s[^1].str.add("mno")
+  s[s.high].str.add("pqr")
+
+  let slen = s.len
+  s[slen - 1].str.add("stu")
+
+  let shigh = s.high
+  s[shigh].str.add("vwx")
+
+  proc foo(): int =
+    echo "foo"
+    shigh
+  s[foo()].str.add("yz")
+  doAssert s[1].str == "defghijklmnopqrstuvwxyz"
+
+block: # #14117
+  type
+    A = object
+      case kind: bool
+      of true:
+        sons: seq[int]
+      else: discard
+
+  var a = A(kind: true)
+  doAssert a.sons.len == 0
+  a.sons.add(1)
+  doAssert a.sons.len == 1
+
+import tables
+
+block: # #13966
+  var t: Table[int8, array[int8, seq[tuple[]]]]
+
+  t[0] = default(array[int8, seq[tuple[]]])
+  t[0][0].add ()
+
+block: # #11783
+  proc fun(): string =
+    discard
+
+  var ret: string
+  ret.add fun()
+  doAssert ret == ""
+
+block: # #12256
+  var x: bool
+
+  doAssert x == false
+
+  reset x
+
+  doAssert x == false
+  doAssert x != true