[gcc r13-4675] gccrs: Add fatal_error when experimental flag is not present

[Arthur Cohen <cohenarthur@gcc.gnu.org>]

https://gcc.gnu.org/g:b07ef39ffbf4e77a586605019c64e2e070915ac3

commit r13-4675-gb07ef39ffbf4e77a586605019c64e2e070915ac3
Author: Arthur Cohen <arthur.cohen@embecosm.com>
Date:   Mon Nov 28 18:22:34 2022 +0100

    gccrs: Add fatal_error when experimental flag is not present
    
    This commits ports over the flag/env variable checking from #1540 which only
    allows compilation using gccrs if a certain flag is specified
    
            gcc/rust/
            * lang.opt (-frust-incomplete-and-experimental-compiler-do-not-use):
            New.
            * rust-session-manager.cc (Session::compile_crate): Check it.
            * Make-lang.in (RUST_SELFTEST_FLAGS): Add it.
            gcc/testsuite/
            * lib/rust.exp (rust_init): Add
            '-frust-incomplete-and-experimental-compiler-do-not-use'.

Diff:
---
 gcc/rust/Make-lang.in            |  2 +-
 gcc/rust/lang.opt                |  4 ++++
 gcc/rust/rust-session-manager.cc | 22 ++++++++++++++++++++++
 gcc/testsuite/lib/rust.exp       |  2 ++
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/Make-lang.in b/gcc/rust/Make-lang.in
index f3a03a3199d..681ac7b3fee 100644
--- a/gcc/rust/Make-lang.in
+++ b/gcc/rust/Make-lang.in
@@ -267,7 +267,7 @@ rust.uninstall:
 # Enable selftests for the rust frontend
 selftest-rust: s-selftest-rust
 
-RUST_SELFTEST_FLAGS = -xrust $(SELFTEST_FLAGS)
+RUST_SELFTEST_FLAGS = -xrust -frust-incomplete-and-experimental-compiler-do-not-use $(SELFTEST_FLAGS)
 RUST_SELFTEST_DEPS = rust1$(exeext) $(SELFTEST_DEPS)
 
 # Run the rust selftests
diff --git a/gcc/rust/lang.opt b/gcc/rust/lang.opt
index 6187fbf2935..63732a636a3 100644
--- a/gcc/rust/lang.opt
+++ b/gcc/rust/lang.opt
@@ -66,6 +66,10 @@ frust-dump-
 Rust Joined RejectNegative
 -frust-dump-<type>	Dump Rust frontend internal information.
 
+frust-incomplete-and-experimental-compiler-do-not-use
+Rust Var(flag_rust_experimental)
+Enable experimental compilation of Rust files at your own risk
+
 frust-max-recursion-depth=
 Rust RejectNegative Type(int) Var(rust_max_recursion_depth) Init(64)
 -frust-max-recursion-depth=integer
diff --git a/gcc/rust/rust-session-manager.cc b/gcc/rust/rust-session-manager.cc
index 6d7f1a85f19..264fb5051b7 100644
--- a/gcc/rust/rust-session-manager.cc
+++ b/gcc/rust/rust-session-manager.cc
@@ -417,6 +417,28 @@ Session::handle_crate_name (const AST::Crate &parsed_crate)
 void
 Session::compile_crate (const char *filename)
 {
+  if (!flag_rust_experimental
+      && !std::getenv ("GCCRS_INCOMPLETE_AND_EXPERIMENTAL_COMPILER_DO_NOT_USE"))
+    rust_fatal_error (
+      Location (), "%s",
+      "gccrs is not yet able to compile Rust code "
+      "properly. Most of the errors produced will be gccrs' fault and not the "
+      "crate you are trying to compile. Because of this, please reports issues "
+      "to us directly instead of opening issues on said crate's "
+      "repository.\n\nOur github repository: "
+      "https://github.com/rust-gcc/gccrs\nOur bugzilla tracker: "
+      "https://gcc.gnu.org/bugzilla/"
+      "buglist.cgi?bug_status=__open__&component=rust&product=gcc\n\n"
+      "If you understand this, and understand that the binaries produced might "
+      "not behave accordingly, you may attempt to use gccrs in an experimental "
+      "manner by passing the following flag:\n\n"
+      "`-frust-incomplete-and-experimental-compiler-do-not-use`\n\nor by "
+      "defining the following environment variable (any value will "
+      "do)\n\nGCCRS_INCOMPLETE_AND_EXPERIMENTAL_COMPILER_DO_NOT_USE\n\nFor"
+      "cargo-gccrs, this means passing\n\n"
+      "GCCRS_EXTRA_FLAGS=\"-frust-incomplete-and-experimental-compiler-do-not-"
+      "use\"\n\nas an environment variable.");
+
   RAIIFile file_wrap (filename);
   if (!file_wrap.ok ())
     {
diff --git a/gcc/testsuite/lib/rust.exp b/gcc/testsuite/lib/rust.exp
index 6993c976304..287905bd544 100644
--- a/gcc/testsuite/lib/rust.exp
+++ b/gcc/testsuite/lib/rust.exp
@@ -149,6 +149,8 @@ proc rust_init { args } {
 	lappend ALWAYS_RUSTFLAGS "additional_flags=$TOOL_OPTIONS"
     }
 
+	lappend ALWAYS_RUSTFLAGS "additional_flags=-frust-incomplete-and-experimental-compiler-do-not-use"	
+	
     verbose -log "ALWAYS_RUSTFLAGS set to $ALWAYS_RUSTFLAGS"
 
     set gcc_warning_prefix "warning:"