[mlir] Fix emitting an error at EOF

[Mogball]

Summary

Emitting at error at EOF will emit the diagnostic past the end of the file. When emitting an error during parsing at EOF, emit it at the previous character.

[jpienaar]

mlir/lib/Parser/Parser.h

72

Could you check on an empty file what happens here?

[Mogball]

mlir/lib/Parser/Parser.h

72

An empty file parses as module {}. A file that has anything in it that is invalid will be fine since there's at least one more character other than EOF.

[rriddle]

Nice!

mlir/lib/Parser/Parser.h

public:
   // as the results of their action.
 
   //===--------------------------------------------------------------------===//
   // Error Handling
   //===--------------------------------------------------------------------===//
 
   /// Emit an error and return failure.
   InFlightDiagnostic emitError(const Twine &message = {}) {
+    // If the error is to be emitted at EOF, move it back one character.
+    if (state.curToken.is(Token::eof)) {
+      return emitError(
+          SMLoc::getFromPointer(state.curToken.getLoc().getPointer() - 1),
+          message);
+    }
     return emitError(state.curToken.getLoc(), message);
   }
   InFlightDiagnostic emitError(SMLoc loc, const Twine &message = {});
 
   /// Encode the specified source location information into an attribute for
   /// attachment to the IR.
   Location getEncodedSourceLocation(SMLoc loc) {
     // If there are no active nested parsers, we can get the encoded source

mlir/test/IR/invalid.mlir

 // -----
 // expected-error@+1 {{expected '"' in string literal}}
 "J// -----
 func @calls(%arg0: i32) {
   // expected-error@+1 {{expected non-function type}}
   %z = "casdasda"(%x) : (ppop32) -> i32
 }
 // -----
-// expected-error@+2 {{expected SSA operand}}
+// expected-error@+1 {{expected SSA operand}}
 func@n(){^b(
 // -----
 
 func @elementsattr_non_tensor_type() -> () {
 ^bb0:
   "foo"(){bar = dense<[4]> : i32} : () -> () // expected-error {{elements literal must be a ranked tensor or vector type}}
 }
 

 !missing_eq_alias type i32 // expected-error {{expected '=' in type alias definition}}
 
 // -----
 
 !missing_kw_type_alias = i32 // expected-error {{expected 'type' in type alias definition}}
 
 // -----
 
-!missing_type_alias = type // expected-error@+2 {{expected non-function type}}
+!missing_type_alias = type // expected-error@+1 {{expected non-function type}}
 
 // -----
 
 !redef_alias = type i32
 !redef_alias = type i32 // expected-error {{redefinition of type alias id 'redef_alias'}}
 
 // -----