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# 9. Processing an Ada Library by an ASIS-Based Tool

When an Ada unit to be processed by some ASIS-based tool makes use of an Ada library, you need to be aware of the following features of using Ada libraries with GNAT:

- An Ada library is a collection of precompiled Ada components. The sources of the Ada components belonging to the library are present, but if your program uses some components from a library, these components are not recompiled by `gnatmake` (except in circumstances described below). For example, `Ada.Text_IO` is not recompiled when you invoke `gnatmake` on a unit that `with`s `Ada.Text_IO`.

- According to the GNAT source-based compilation model, the spec of a library component is processed when an application unit depending on such a component is compiled, but the body of the library component is not processed. As a result, if you invoke `gnatmake` to create a set of tree files covering a given program, and if this program references an entity from an Ada library, then the set of tree files created by such a call will contain only specs, but not bodies for library components.

- Any GNAT installation contains the GNAT Run-Time Library (RTL) as a precompiled Ada library. In some cases, a GNAT installation may contain some other libraries (such as Win32Ada Binding on a Windows GNAT platform).

- In ASIS-for-GNAT, there is no standard way to define whether a given `Compilation_Unit` belongs to some precompiled Ada library other than the GNAT Run-Time Library (some heuristics may be added to `Asis.Extensions`). ASIS-for-GNAT classifies (by means of the `Asis.Compilation_Units.Unit_Origin` query) a unit as `A_Predefined_Unit`, if it is from the Run-Time Library and if it is mentioned in the Ada Reference Manual, Annex A, Paragraph 2 as an Ada 95 predefined unit; a unit is classified as `An_Implementation_Unit` if is belongs to Run-Time Library but is not mentioned in the paragraph just cited. Components of Ada libraries other than the Run-Time Library are always classified as `An_Application_Unit`;

- It is possible to recompile the components of the Ada libraries used by a given program. To do this, you have to invoke `gnatmake` for this program with the ``-a'` option. If you create a set of tree files for your program by invoking `gnatmake` with the ``-a'` option, the resulting set of tree files will contain all the units needed by this program to make up a complete partition.

Therefore, there are two possibilities for an ASIS-based tool if processing (or avoiding processing) of Ada libraries is important for the functionality of the tool:

- If the tool is not to process components of Ada libraries, then a set of tree files for this tool may be created by invoking `gnatmake` without the ``-a'` option (this is the usual way of using `gnatmake`). When the tool encounters a `Compilation_Unit` which represents a spec of some library unit, and for which `Asis.Compilation_Units.Is_Body_Required` returns `True`, but `Asis.Compilation_Units.Corresponding_Body` yields a result of `A_Nonexistent_Body` kind, then the tool may conclude that this library unit belongs to some precompiled Ada library.

- If a tool needs to process all the Ada compilation units making up a program, then a set of tree files for this program should be created by invoking `gnatmake` with the ``-a'` option.

You can use `Asis.Compilation_units.Unit_Origin` to filter out Run-Time Library components.

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