Emit error when range pattern is empty

gcc/rust/checks/errors/rust-ast-validation.cc

@@ -21,6 +21,8 @@
 #include "rust-diagnostics.h"
 #include "rust-item.h"
 #include "rust-keyword-values.h"
+#include "rust-pattern.h"
+#include "safe-ctype.h"
 
 namespace Rust {
 
@@ -180,4 +182,40 @@ ASTValidation::visit (AST::Module &module)
   AST::ContextualASTVisitor::visit (module);
 }
 
+void
+ASTValidation::visit (AST::RangePattern &pattern)
+{
+  if (pattern.get_has_lower_bound () && pattern.get_has_upper_bound ())
+    {
+      auto &lower = pattern.get_lower_bound ();
+      auto &upper = pattern.get_upper_bound ();
+
+      if (lower->get_bound_type () == AST::RangePatternBound::LITERAL
+	  && upper->get_bound_type () == AST::RangePatternBound::LITERAL)
+	{
+	  int lower_value{};
+	  int upper_value{};
+	  // if numeric range, get lower and upper numeric values
+	  if (ISDIGIT (lower->as_string ()[0]))
+	    {
+	      lower_value = std::stoi (lower->as_string ());
+	      upper_value = std::stoi (upper->as_string ());
+	    }
+	  // else if character range, get lower and upper ASCII values
+	  else
+	    {
+	      lower_value = lower->as_string ()[0];
+	      upper_value = upper->as_string ()[0];
+	    }
+	  // raise error if range is empty
+	  if (lower_value > upper_value)
+	    {
+	      rust_error_at (
+		pattern.get_locus (), ErrorCode::E0030,
+		"lower range bound must be less than or equal to upper");
+	    }
+	}
+    }
+}
+
 } // namespace Rust

gcc/rust/checks/errors/rust-ast-validation.h

@@ -43,6 +43,7 @@ class ASTValidation : public AST::ContextualASTVisitor
   virtual void visit (AST::Function &function);
   virtual void visit (AST::Trait &trait);
   virtual void visit (AST::TraitFunctionDecl &decl);
+  virtual void visit (AST::RangePattern &pattern);
 };
 
 } // namespace Rust

gcc/rust/parse/rust-parse-impl.h

@@ -10435,7 +10435,7 @@ Parser<ManagedTokenSource>::parse_literal_or_range_pattern ()
 
       return std::unique_ptr<AST::RangePattern> (
 	new AST::RangePattern (std::move (lower), std::move (upper),
-			       range_lower->get_locus ()));
+			       range_lower->get_locus (), next->get_id () == ELLIPSIS));
     }
   else
     {

gcc/testsuite/rust/compile/issue-2794.rs

@@ -0,0 +1,15 @@
+fn main() {
+    let mut x = 11;
+    match x {
+        2..=1 => x = 6,
+        // { dg-error "lower range bound must be less than or equal to upper" "" { target *-*-* } .-1 }
+        _ => x = 7,
+    }
+
+    let mut y = 'a';
+    match y {
+        'z'..='y' => y = 'b',
+        // { dg-error "lower range bound must be less than or equal to upper" "" { target *-*-* } .-1 }
+        _ => y = 'c',
+    }
+}