fix bugs with dot & call operators [backport] (#20931)

* better error messages for dot operators [backport]

fixes #13063

* also fixes #7777

* fix #6981 and #9831 too

* fix

* minor improvement

* sus test fixes

* make test multiplatform lol

* fix nimsuggest test, extra improvements

tests/specialops/terrmsgs.nim

@@ -0,0 +1,76 @@
+discard """
+action: reject
+cmd: '''nim check $options $file'''
+matrix: "; -d:testWithout"
+"""
+
+when not defined(testWithout): # test for same errors before and after
+  {.experimental: "dotOperators".}
+  {.experimental: "callOperator".}
+
+# issue #13063
+
+block:
+  type Foo = object
+  type Bar = object
+    x1: int
+  var b: Bar
+  block:
+    template `.`(a: Foo, b: untyped): untyped = 123
+    echo b.x #[tt.Error
+          ^ undeclared field: 'x' for type terrmsgs.Bar [type declared in terrmsgs.nim(15, 8)]]#
+  block:
+    template `.()`(a: Foo, b: untyped): untyped = 123
+    echo b.x() #[tt.Error
+          ^ attempting to call undeclared routine: 'x']#
+  block:
+    template `.=`(a: Foo, b: untyped, c: untyped) = b = c
+    b.x = 123 #[tt.Error
+        ^ undeclared field: 'x=' for type terrmsgs.Bar [type declared in terrmsgs.nim(15, 8)]]#
+    # yeah it says x= but does it matter in practice
+  block:
+    template `()`(a: Foo, b: untyped, c: untyped) = echo "something"
+
+    # completely undeclared::
+    xyz(123) #[tt.Error
+    ^ undeclared identifier: 'xyz']#
+
+    # already declared routine:
+    min(123) #[tt.Error
+       ^ type mismatch: got <int literal(123)>]#
+
+    # non-routine type shows `()` overloads:
+    b(123) #[tt.Error
+     ^ attempting to call routine: 'b']#
+
+    echo b.x #[tt.Error
+          ^ undeclared field: 'x' for type terrmsgs.Bar [type declared in terrmsgs.nim(15, 8)]]#
+    echo b.x() #[tt.Error
+          ^ attempting to call undeclared routine: 'x']#
+
+# issue #7777
+
+import macros
+
+block:
+  type TestType = object
+    private_field: string
+
+  when false:
+    template getField(obj, field: untyped): untyped = obj.field
+
+  macro `.`(obj: TestType, field: untyped): untyped =
+    let private = newIdentNode("private_" & $field)
+    result = quote do:
+      `obj`.getField(`private`) #[tt.Error
+           ^ attempting to call undeclared routine: 'getField']#
+
+  var tt: TestType
+  discard tt.field
+
+block: # related to issue #6981
+  proc `()`(a:string, b:string):string = a & b
+  proc mewSeq[T](a,b:int)=discard
+  proc mewSeq[T](c:int)= discard
+  mewSeq[int]() #[tt.Error
+             ^ type mismatch: got <>]#

tests/specialops/tnewseq.nim

@@ -0,0 +1,22 @@
+# issue #6981
+
+import std/assertions
+
+{.experimental: "callOperator".}
+
+block: # issue #6981
+  proc `()`(a:string, b:string):string = a & b
+
+  var s = newSeq[int](3)
+
+  doAssert s == @[0, 0, 0]
+
+block: # generalized example from #6981
+  proc mewSeq[T](a: int)=discard
+  proc mewSeq[T]()= discard
+  mewSeq[int]()
+
+block: # issue #9831
+  type Foo = object
+  proc `()`(foo: Foo) = discard
+  let x = newSeq[int]()