9.4. Preprocessing

Libadalang’s integrated preprocessor works thanks to the file reader mechanism: you create a file reader that knows which files to preprocess and with which parameters, and you pass that file reader when creating the analysis context.

9.4.1. Input source

prep-data.txt

"os.ads" -Dos=windows

os.ads

package OS is
   # if OS = "linux" then
      Name : constant String := "gnu-linux";
   # elsif OS = "windows" then
      Name : constant String := "microsoft-windows";
   # else
      Name : constant String := "unknown";
   # end if;
end OS;

print_os.adb

with Ada.Text_IO; use Ada.Text_IO;

with OS;

procedure Print_OS is
begin
   Put_Line (OS.Name);
end Print_OS;

9.4.2. Sample code

9.4.2.1. Python

import libadalang as lal


# Let the file reader find preprocessor data files in the
# current directory.
path = ["."]

# Create the preprocessor file reader from the
# "prep-data.txt" preprocessor file. Force the "blank lines"
# mode to preserve line numbers in the preprocessed code.
fr = lal.FileReader.create_preprocessor_from_file(
    filename="prep-data.txt",
    path=path,
    line_mode=lal.FileReader.LineMode.blank_lines,
)

# Create a context using this preprocessor configuration and
# start using Libadalang's analysis the usual way...
ctx = lal.AnalysisContext(file_reader=fr)
u = ctx.get_from_file("print_os.adb")

for node in u.root.findall(lambda n: n.text == "Name"):
    # Fetch the declaration that this "Name" identifier
    # references.
    decl = node.p_referenced_decl()
    print(node)
    print(f"  references {decl}")
    print()

    # Show the text of the unit that contain that
    # declaration, with line numbers.
    print("Unit text:")
    for i, line in enumerate(
        decl.unit.text.split("\n"), 1
    ):
        print(f"{str(i).rjust(2)} | {line}")

9.4.2.2. Ada

with Ada.Text_IO; use Ada.Text_IO;

with GNATCOLL.File_Paths; use GNATCOLL.File_Paths;
with GNATCOLL.Strings; use GNATCOLL.Strings;

with Langkit_Support.File_Readers; use Langkit_Support.File_Readers;
with Langkit_Support.Text;         use Langkit_Support.Text;

with Libadalang.Analysis;      use Libadalang.Analysis;
with Libadalang.Common;        use Libadalang.Common;
with Libadalang.Preprocessing; use Libadalang.Preprocessing;

procedure Main is

   Path : constant Any_Path := Create_Path
     (Directories => (1 .. 0 => <>), CWD => If_Empty);
   --  Let the file reader find preprocessor data files in
   --  the current directory.

   FR  : constant File_Reader_Reference :=
     Create_Preprocessor_From_File
       ("prep-data.txt", Path, Blank_Lines);
   --  Create the preprocessor file reader from the
   --  "prep-data.txt" preprocessor file. Force the "blank
   --  lines" mode to preserve line numbers in the
   --  preprocessed code.

   Ctx : constant Analysis_Context :=
     Create_Context (File_Reader => FR);
   U   : constant Analysis_Unit :=
     Ctx.Get_From_File ("print_os.adb");
   --  Create a context using this preprocessor
   --  configuration and start using Libadalang's analysis
   --  the usual way...

   -----------
   -- Visit --
   -----------

   function Visit (Node : Ada_Node'Class) return Visit_Status is
   begin
      if Node.Text = "Name" then

         --  Fetch the declaration that this "Name"
         --  identifier references.

         declare
            Ref : constant Basic_Decl :=
              Node.As_Identifier.P_Referenced_Decl;
         begin
            Put_Line (Node.Image);
            Put_Line ("  references " & Ref.Image);
            New_Line;

            --  Show the text of the unit that contain that
            --  declaration, with line numbers.

            Put_Line ("Unit text:");
            declare
               Text   : constant XString :=
                 To_XString (To_UTF8 (Ref.Unit.Text));
               Lineno : Positive := 1;
            begin
               for Line of Text.Split (ASCII.LF) loop
                  declare
                     Lineno_Img : constant String :=
                       " " & Lineno'Image;
                     Prefix     : String renames Lineno_Img
                       (Lineno_Img'Last - 2
                        .. Lineno_Img'Last);
                  begin
                     Put (Prefix & " | ");
                     Put_Line (To_String (Line));
                     Lineno := Lineno + 1;
                  end;
               end loop;
            end;
         end;
      end if;
      return Into;
   end Visit;

begin
   U.Root.Traverse (Visit'Access);
end Main;

9.4.2.3. Output

<Id "Name" print_os.adb:7:17-7:21>
  references <ObjectDecl ["Name"] os.ads:6:7-6:53>

Unit text:
| package OS is
|    Bits : constant := 32;
|
|
|
|       Name : constant String := "microsoft-windows";
|
|
|
| end OS;
|