Fix rust breakage with nr2

Nr2 did not emit the correct error message for break identifier "rust".

gcc/rust/ChangeLog:

	* resolve/rust-late-name-resolver-2.0.cc (Late::visit): Add "rust"
	identifier detection akin to nr1.
	(funny_ice_finalizer): Copy ICE finalizer from nr1.
	* resolve/rust-late-name-resolver-2.0.h: Add funny_error member
	context state.

gcc/testsuite/ChangeLog:

	* rust/compile/nr2/exclude: Remove break-rust3.rs from exclude list.

Signed-off-by: Pierre-Emmanuel Patry <[email protected]>

gcc/rust/resolve/rust-late-name-resolver-2.0.cc

@@ -18,6 +18,7 @@
 
 #include "optional.h"
 #include "rust-ast-full.h"
+#include "rust-ast.h"
 #include "rust-hir-map.h"
 #include "rust-late-name-resolver-2.0.h"
 #include "rust-default-resolver.h"
@@ -26,6 +27,7 @@
 #include "rust-system.h"
 #include "rust-tyty.h"
 #include "rust-hir-type-check.h"
+#include "diagnostic.h"
 
 namespace Rust {
 namespace Resolver2_0 {
@@ -176,6 +178,73 @@ Late::visit (AST::SelfParam &param)
 				   param.get_node_id ());
 }
 
+void
+Late::visit (AST::BreakExpr &expr)
+{
+  if (expr.has_break_expr ())
+    {
+      auto &break_expr = expr.get_break_expr ();
+      if (break_expr.get_ast_kind () == AST::Kind::IDENTIFIER)
+	{
+	  /* This is a break with an expression, and the expression is
+	     just a single identifier.  See if the identifier is either
+	     "rust" or "gcc", in which case we have "break rust" or "break
+	     gcc", and so may need to emit our funny error.  We cannot yet
+	     emit the error here though, because the identifier may still
+	     be in scope, and ICE'ing on valid programs would not be very
+	     funny.  */
+	  std::string ident
+	    = static_cast<AST::IdentifierExpr &> (expr.get_break_expr ())
+		.as_string ();
+	  if (ident == "rust" || ident == "gcc")
+	    funny_error = true;
+	}
+    }
+
+  DefaultResolver::visit (expr);
+
+  funny_error = false;
+}
+
+/* The "break rust" Easter egg.
+
+   Backstory: once upon a time, there used to be a bug in rustc: it would ICE
+   during typechecking on a 'break' with an expression outside of a loop.  The
+   issue has been reported [0] and fixed [1], but in recognition of this, as a
+   special Easter egg, "break rust" was made to intentionally cause an ICE.
+
+   [0]: https://github.com/rust-lang/rust/issues/43162
+   [1]: https://github.com/rust-lang/rust/pull/43745
+
+   This was made in a way that does not break valid programs: namely, it only
+   happens when the 'break' is outside of a loop (so invalid anyway).
+
+   GCC Rust supports this essential feature as well, but in a slightly
+   different way.  Instead of delaying the error until type checking, we emit
+   it here in the resolution phase.  We, too, only do this to programs that
+   are already invalid: we only emit our funny ICE if the name "rust" (which
+   must be immediately inside a break-with-a-value expression) fails to
+   resolve.  Note that "break (rust)" does not trigger our ICE, only using
+   "break rust" directly does, and only if there's no "rust" in scope.  We do
+   this in the same way regardless of whether the "break" is outside of a loop
+   or inside one.
+
+   As a GNU extension, we also support "break gcc", much to the same effect,
+   subject to the same rules.  */
+
+/* The finalizer for our funny ICE.  This prints a custom message instead of
+   the default bug reporting instructions, as there is no bug to report.  */
+
+static void ATTRIBUTE_NORETURN
+funny_ice_finalizer (diagnostic_context *context,
+		     const diagnostic_info *diagnostic, diagnostic_t diag_kind)
+{
+  gcc_assert (diag_kind == DK_ICE_NOBT);
+  default_diagnostic_finalizer (context, diagnostic, diag_kind);
+  fnotice (stderr, "You have broken GCC Rust. This is a feature.\n");
+  exit (ICE_EXIT_CODE);
+}
+
 void
 Late::visit (AST::IdentifierExpr &expr)
 {
@@ -191,6 +260,13 @@ Late::visit (AST::IdentifierExpr &expr)
     {
       resolved = type;
     }
+  else if (funny_error)
+    {
+      diagnostic_finalizer (global_dc) = funny_ice_finalizer;
+      emit_diagnostic (DK_ICE_NOBT, expr.get_locus (), -1,
+		       "are you trying to break %s? how dare you?",
+		       expr.as_string ().c_str ());
+    }
   else
     {
       rust_error_at (expr.get_locus (),

gcc/rust/resolve/rust-late-name-resolver-2.0.h

@@ -45,6 +45,7 @@ class Late : public DefaultResolver
 
   // resolutions
   void visit (AST::IdentifierExpr &) override;
+  void visit (AST::BreakExpr &) override;
   void visit (AST::PathInExpression &) override;
   void visit (AST::TypePath &) override;
   void visit (AST::StructExprStruct &) override;
@@ -57,6 +58,8 @@ class Late : public DefaultResolver
 private:
   /* Setup Rust's builtin types (u8, i32, !...) in the resolver */
   void setup_builtin_types ();
+
+  bool funny_error;
 };
 
 // TODO: Add missing mappings and data structures

gcc/testsuite/rust/compile/nr2/exclude

@@ -4,7 +4,6 @@ attr_deprecated_2.rs
 bad=file-name.rs
 bounds1.rs
 break-rust2.rs
-break-rust3.rs
 macros/builtin/eager1.rs
 macros/builtin/eager2.rs
 macros/builtin/recurse2.rs