#645 Access to global duplicated symbol is captured by local symbol

[fxm (freebasic.net)]

From a scope block, the syntax for accessing a duplicated symbol defined in a namespace/UDT is captured by the local symbol, making impossible the desired access.

---

Simple example with a procedure inside a namespace:

Namespace NS
  Dim x As Integer = 3
  Sub S ()
    Dim x As Integer = 4
    Print "From Sub() in Namespace 'NS', access to 'NS.x' is captured by local 'x'"
    Print "x="; x, "NS.x="; NS.x
  End Sub
End Namespace

NS.S()
Sleep

Output:

From Sub() in Namespace 'NS', access to 'NS.x' is captured by local 'x'
x= 4          NS.x= 4

---

More complex example with 3 different failing cases:

• procedure inside a namespace
• procedure inside global namescape

• member procedure inside UDT

  Dim Shared x As Integer = 1

  Type UDT
  Dim As Integer dummy
  Static As Integer x
  Declare Static Sub S ()
  End Type
  Dim As Integer UDT.x = 2

  Namespace NS
  Dim x As Integer = 3
  Sub S ()
  Dim x As Integer = 4
  Print "From Sub() in Namespace 'NS', access to 'NS.x' is captured by local 'x'"
  Print "x="; x, "NS.x="; NS.x, "UDT.x="; UDT.x, ".x="; .x
  End Sub
  End Namespace

  Sub S ()
  Dim x As Integer = 4
  Print "From Sub() in Global Namespace '.', access to '.x' is captured by local 'x'"
  Print "x="; x, "NS.x="; NS.x, "UDT.x="; UDT.x, ".x="; .x
  End Sub

  Static Sub UDT.S ()
  Dim x As Integer = 4
  Print "From Sub() in Type 'UDT', access to 'UDT.x' is captured by local 'x'"
  Print "x="; x, "NS.x="; NS.x, "UDT.x="; UDT.x, ".x="; .x
  End Sub

  NS.S()
  Print
  S()
  Print
  UDT.S()
  sleep

Output:

From Sub() in Namespace 'NS', access to 'NS.x' is captured by local 'x'
x= 4          NS.x= 4       UDT.x= 2      .x= 1

From Sub() in Global Namespace '.', access to '.x' is captured by local 'x'
x= 4          NS.x= 3       UDT.x= 2      .x= 4

From Sub() in Type 'UDT', access to 'UDT.x' is captured by local 'x'
x= 4          NS.x= 3       UDT.x= 4      .x= 1

[fxm (freebasic.net)]

Check if there is not a link with #581 Locals break/override THIS access to inherited members

[dkl]

Indeed, I think [#581] is caused by this.

Perhaps this could be fixed by making each scope have its own namespace - but that's a massive change to fbc's symbol tables, that will surely have a negative impact on scope creation & symbol lookup performance, or will even require lots of the code to be rewritten.

[Jeff Marshall]

Indeed, first glance there is a temptation to rewrite the symbol database, but that would probably take months. Digging deep in to the compiler internals, I have come up with 2 underlying causes which could be improved incrementally:

• the global namespace and current namespace are both internally represented by a 'NULL' FBSYMBOL depending on where you look.
• local symbols added to a namespace should not be allowed to be accessed by explicit use of that namespace

I'm working on a pull request to address these 2 issues for shared variables (and arrays) that starts the effort to do 2 things:

• internally use explicit namespace resolution, including the global namespace resolution operator '.' and '..' prefix rather than rely on a default of 'NULL'
• when symbols are referenced by explicit namespace skip over any local symbols in the FBSYMCHAIN

[fxm (freebasic.net)]

The linked #581 "Locals break/override THIS access to inherited members" is less troublesome because exists a simple workaround that is to access with BASE.[BASE.]...

At opposite, faced with this bug above, there is only one possibility of workaround to access the real value of "UDT.x". This is: "Cast(UDT Ptr, 0)->x".
No workaround for others (except differentiate the symbol names!).

[fxm (freebasic.net)]

Another variant:

In the following example, not only does the local array 'd ()' hide the global variable 'd', but also captures the data-type of the global variable for its own data-type if it is not specified in 'redim ...':

dim as integer d

scope
  redim d(10)   '' should induce a compiler error message
  'd = 1        '' error 72: Array access, index expected
  print d(10)
end scope

[fxm (freebasic.net)]

Similar behavior:

Type UDT
  Dim As Integer I
  Declare Sub test ()
  Declare Static Sub test (Byref u As UDT)
End Type

Print @UDT.test  '' error 209: Illegal non-static member access, UDT.TEST in 'Print @UDT.test'

[edit]
Behavior normal with overload procedures, because by default, the first is choosen.
Can be solved with:
Print ProcPtr(UDT.test, Sub(Byref As UDT))

[Jeff Marshall]

Fixed / changed by pull request sf.net # 645 - namespace and scope resolution on variables #346 (github.com)

Commit: [ec1e19665cdf3153e058cda5722689ad3fe51ee8]