[gcc/devel/rust/master] Merge #1362

[gcc/devel/rust/master] Merge #1362

[Thomas Schwinge]

https://gcc.gnu.org/g:fd2bd659e44e5b7fea92bc34a4864f057f387490

commit fd2bd659e44e5b7fea92bc34a4864f057f387490
Merge: 67f9b173b90 2d1378f7310
Author: bors[bot] <26634292+bors[bot]@users.noreply.github.com>
Date:   Fri Jul 15 16:09:43 2022 +0000

    Merge #1362
    
    1362: extern crate loading  r=philberty a=philberty
    
    WIP still trying to write dejagnu to enable automated tests
    
    Extern crates statements to tell the front-end to look for another library.
    The mechanism here is heavily inspired from gccgo, so when we compile a
    library for example we invoke:
    
    ```
      gccrs -g -O2 -frust-crate=mylib -c src/lib.rs -o src/mylib.o
    ```
    
    All going well this object file will now contain extra data inside
    .rust-export section inside the object file which will be preserved inside
    archives and shared objects. When we have another application which uses
    this library 'mylib'.
    
    ```rust
      extern crate mylib;
      use mylib::foo;
    
      fn main() {
        foo();
      }
    ```
    
    We compile using:
    
    ```
    gcc -g -O2 -frust-crate=test -c src/main.rs -o src/main.o
    ```
    
    When the extern crate line is hit the front-end will look for mylib.o,
    libmylib.a, mylib.rox. If it finds a raw object file it will read the
    .rust-export section directly from the object for the public metadata
    such as public functions, types constants etc. If it fails to find an
    object it might find .rox which is the objdump of the .rust-export to a
    raw file, it might even find libmylib.a and read the export directly out
    of the archive file reusing code from gccgo to do so.
    
    The full compiler pipeline is reused here, so the metatadata is actually
    just real rust code. The benifit here is that Rust supports exporting,
    macros and generics so this requires the name-resolution and type info
    all to be generated and inserted into the apropriate context classes. Since
    the metadata is real rust code it means we can reuse the full pipeline to
    generate the code as nessecary. So for the simple case of a public struct
    we simply emit the AST dump of this struct directly into the metadata. If
    its a non-generic public function we emit and extern rust abi block for
    that function. If its a trait we can simply emit the trait with the public
    memebers. Generics are more complicated since we need to emit the function
    fully for it to be compiled correctly this still needs tests to be added.
    The hardest part is non generic impl blocks which is still a WIP.
    
    To finally link the two crates together you run:
    
    ```
    gcc -g -O2 -o rust-program.exe src/main.o src/mylib.o
    ```
    
    Fixes: 1169
    
    
    Co-authored-by: Philip Herron <philip.herron@embecosm.com>

Diff:

 gcc/rust/Make-lang.in                         |  12 +-
 gcc/rust/ast/rust-ast-dump.cc                 |  69 +-
 gcc/rust/ast/rust-ast-dump.h                  |   1 +
 gcc/rust/expand/rust-attribute-visitor.cc     |  17 +-
 gcc/rust/lang.opt                             |   8 +
 gcc/rust/metadata/rust-export-metadata.cc     | 385 +++++++++++
 gcc/rust/metadata/rust-export-metadata.h      |  85 +++
 gcc/rust/metadata/rust-extern-crate.cc        | 173 +++++
 gcc/rust/metadata/rust-extern-crate.h         |  55 ++
 gcc/rust/metadata/rust-import-archive.cc      | 885 ++++++++++++++++++++++++++
 gcc/rust/metadata/rust-imports.cc             | 441 +++++++++++++
 gcc/rust/metadata/rust-imports.h              | 257 ++++++++
 gcc/rust/resolve/rust-ast-resolve-toplevel.h  |  60 +-
 gcc/rust/rust-object-export.cc                |   6 -
 gcc/rust/rust-session-manager.cc              | 110 +++-
 gcc/rust/rust-session-manager.h               |  19 +-
 gcc/testsuite/rust/link/generic_function_0.rs |   7 +
 gcc/testsuite/rust/link/generic_function_1.rs |   3 +
 gcc/testsuite/rust/link/link.exp              | 163 +++++
 gcc/testsuite/rust/link/simple_function_0.rs  |   7 +
 gcc/testsuite/rust/link/simple_function_1.rs  |   3 +
 gcc/testsuite/rust/link/trait_import_0.rs     |  19 +
 gcc/testsuite/rust/link/trait_import_1.rs     |   6 +
 23 files changed, 2740 insertions(+), 51 deletions(-)