Add an error message about known reserved words (#322)

pol-core/bscript/compiler/file/ErrorListener.cpp

@@ -1,10 +1,19 @@
 #include "ErrorListener.h"
 
+#include <set>
+
+#include "clib/maputil.h"
 #include "compiler/Profile.h"
 #include "compiler/Report.h"
 
 namespace Pol::Bscript::Compiler
 {
+std::set<std::string, Clib::ci_cmp_pred> easily_overlooked_reserved_words = {
+    "as", "byval", "double", "downto", "float", "hash",
+    "in", "integer", "is", "long", "out", "real",
+    "signed", "stack", "step", "string", "to", "unsigned"
+};
+
 ErrorListener::ErrorListener( std::string pathname, Profile& profile )
     : pathname( std::move( pathname ) ), profile( profile )
 {
@@ -19,10 +28,21 @@ void ErrorListener::propagate_errors_to( Report& report, const SourceFileIdentif
   }
 }
 
-void ErrorListener::syntaxError( antlr4::Recognizer*, antlr4::Token* /*offendingSymbol*/,
+void ErrorListener::syntaxError( antlr4::Recognizer*, antlr4::Token* offendingSymbol,
                                  size_t line, size_t charPositionInLine, const std::string& msg,
                                  std::exception_ptr )
 {
+  if ( offendingSymbol )
+  {
+    std::string symbol = offendingSymbol->getText();
+    if ( easily_overlooked_reserved_words.count( symbol ) )
+    {
+      fmt::Writer w;
+      w << "Did not expect reserved word '" << symbol << "' in this context.\n";
+      error_messages.push_back( { w.str(), line, charPositionInLine + 1 } );
+    }
+  }
+
   error_messages.push_back( { msg, line, charPositionInLine+1 } );
 }
 

testsuite/escript/errors/errors004-reserved-word-as-argument-name.err2

@@ -1 +1 @@
-errors004-reserved-word-as-argument-name.src:3:13: error: extraneous input 'downto' expecting {'unused', ')', IDENTIFIER}
+errors004-reserved-word-as-argument-name.src:3:13: error: Did not expect reserved word 'downto' in this context.

testsuite/escript/errors/errors010-reserved-word-syntax-error.err1

@@ -0,0 +1 @@
+Non-identifier declared as a variable: 'is'

testsuite/escript/errors/errors010-reserved-word-syntax-error.err2

@@ -0,0 +1 @@
+errors010-reserved-word-syntax-error.src:1:5: error: Did not expect reserved word 'is' in this context.

testsuite/escript/errors/errors010-reserved-word-syntax-error.src

@@ -0,0 +1,2 @@
+var is := 1;
+print("the value is " + is);