[FEATURE][needs-docs] Rework expression parser for unknown functions (#6840)

* [FEATURE][needs-docs] Rework expression parser for unknown functions

* Remove old comment

* Rename NAME and update tests

* Change COLUMN_REF to QUOTED_COLUMN_REF

Author: NathanW2

src/core/qgsexpressionlexer.ll

@@ -128,16 +128,16 @@ non_ascii    [\x80-\xFF]
 
 col_first    [A-Za-z_]|{non_ascii}
 col_next     [A-Za-z0-9_]|{non_ascii}
-column_ref  {col_first}{col_next}*
+identifier  {col_first}{col_next}*
 
 deprecated_function "$"[xXyY]_?[aA][tT]
-special_col "$"{column_ref}
-variable "@"{column_ref}
+special_col "$"{identifier}
+variable "@"{identifier}
 
-named_node {column_ref}{white}*":="{white}*
+named_node {identifier}{white}*":="{white}*
 
 col_str_char  "\"\""|[^\"]
-column_ref_quoted  "\""{col_str_char}*"\""
+identifier_quoted  "\""{col_str_char}*"\""
 
 dig         [0-9]
 num_int     {dig}+
@@ -220,17 +220,17 @@ string      "'"{str_char}*"'"
 
 {string}  { TEXT_FILTER(stripText); return STRING; }
 
-{deprecated_function} { TEXT; return FUNCTION; }
+{deprecated_function} { TEXT; return NAME; }
 
 {named_node} { TEXT_FILTER(stripNamedText); return NAMED_NODE; }
 
 {special_col}        { TEXT; return SPECIAL_COL; }
 
 {variable}        { TEXT; return VARIABLE; }
 
-{column_ref}         { TEXT; return QgsExpression::isFunctionName(*yylval->text) ? FUNCTION : COLUMN_REF; }
+{identifier}         { TEXT; return NAME; }
 
-{column_ref_quoted}  { TEXT_FILTER(stripColumnRef); return COLUMN_REF; }
+{identifier_quoted}  { TEXT_FILTER(stripColumnRef); return QUOTED_COLUMN_REF; }
 
 {white}    /* skip blanks and tabs */
 

src/core/qgsexpressionparser.yy

@@ -125,7 +125,7 @@ void addParserLocation(YYLTYPE* yyloc, QgsExpressionNode *node)
 // tokens for conditional expressions
 %token CASE WHEN THEN ELSE END
 
-%token <text> STRING COLUMN_REF FUNCTION SPECIAL_COL VARIABLE NAMED_NODE
+%token <text> STRING QUOTED_COLUMN_REF NAME SPECIAL_COL VARIABLE NAMED_NODE
 
 %token COMMA
 
@@ -203,14 +203,12 @@ expression:
     | expression CONCAT expression    { $$ = BINOP($2, $1, $3); }
     | NOT expression                  { $$ = new QgsExpressionNodeUnaryOperator($1, $2); }
     | '(' expression ')'              { $$ = $2; }
-    | FUNCTION '(' exp_list ')'
+    | NAME '(' exp_list ')'
         {
           int fnIndex = QgsExpression::functionIndex(*$1);
           delete $1;
           if (fnIndex == -1)
           {
-            // this should not actually happen because already in lexer we check whether an identifier is a known function
-            // (if the name is not known the token is parsed as a column)
             QgsExpression::ParserError::ParserErrorType errorType = QgsExpression::ParserError::FunctionUnknown;
             parser_ctx->currentErrorType = errorType;
             exp_error(&yyloc, parser_ctx, "Function is not known");
@@ -240,14 +238,12 @@ expression:
           addParserLocation(&@1, $$);
         }
 
-    | FUNCTION '(' ')'
+    | NAME '(' ')'
         {
           int fnIndex = QgsExpression::functionIndex(*$1);
           delete $1;
           if (fnIndex == -1)
           {
-            // this should not actually happen because already in lexer we check whether an identifier is a known function
-            // (if the name is not known the token is parsed as a column)
             QgsExpression::ParserError::ParserErrorType errorType = QgsExpression::ParserError::FunctionUnknown;
             parser_ctx->currentErrorType = errorType;
             exp_error(&yyloc, parser_ctx, "Function is not known");
@@ -276,7 +272,8 @@ expression:
     | CASE when_then_clauses ELSE expression END  { $$ = new QgsExpressionNodeCondition($2,$4); }
 
     // columns
-    | COLUMN_REF                  { $$ = new QgsExpressionNodeColumnRef( *$1 ); delete $1; }
+    | NAME                  { $$ = new QgsExpressionNodeColumnRef( *$1 ); delete $1; }
+    | QUOTED_COLUMN_REF                  { $$ = new QgsExpressionNodeColumnRef( *$1 ); delete $1; }
 
     // special columns (actually functions with no arguments)
     | SPECIAL_COL

tests/src/core/testqgsexpression.cpp

@@ -206,7 +206,7 @@ class TestQgsExpression: public QObject
       QTest::newRow( "invalid character" ) << "@" << false;
       QTest::newRow( "invalid column reference" ) << "my col" << false;
       QTest::newRow( "invalid binary operator" ) << "1+" << false;
-      QTest::newRow( "invalid function no params" ) << "cos" << false;
+      QTest::newRow( "invalid function not known no args" ) << "watwat()" << false;
       QTest::newRow( "invalid function not known" ) << "coz(1)" << false;
       QTest::newRow( "invalid operator IN" ) << "n in p" << false;
       QTest::newRow( "empty node list" ) << "1 in ()" << false;
@@ -1362,10 +1362,12 @@ class TestQgsExpression: public QObject
       fields.append( QgsField( QStringLiteral( "x1" ) ) );
       fields.append( QgsField( QStringLiteral( "x2" ) ) );
       fields.append( QgsField( QStringLiteral( "foo" ), QVariant::Int ) );
+      fields.append( QgsField( QStringLiteral( "sin" ), QVariant::Int ) );
 
       QgsFeature f;
-      f.initAttributes( 3 );
+      f.initAttributes( 4 );
       f.setAttribute( 2, QVariant( 20 ) );
+      f.setAttribute( 3, QVariant( 10 ) );
 
       QgsExpressionContext context = QgsExpressionContextUtils::createFeatureBasedContext( f, fields );
 
@@ -1385,6 +1387,22 @@ class TestQgsExpression: public QObject
       QCOMPARE( exp2.hasEvalError(), true );
       QVariant res2 = exp2.evaluate( &context );
       QCOMPARE( res2.type(), QVariant::Invalid );
+
+      // Has field called sin and function
+      QgsExpression exp3( QStringLiteral( "sin" ) );
+      prepareRes = exp3.prepare( &context );
+      QCOMPARE( prepareRes, true );
+      QCOMPARE( exp3.hasEvalError(), false );
+      res = exp3.evaluate( &context );
+      QCOMPARE( res.type(), QVariant::Int );
+      QCOMPARE( res.toInt(), 10 );
+
+      QgsExpression exp4( QStringLiteral( "sin(3.14)" ) );
+      prepareRes = exp4.prepare( &context );
+      QCOMPARE( prepareRes, true );
+      QCOMPARE( exp4.hasEvalError(), false );
+      res = exp4.evaluate( &context );
+      QCOMPARE( res.toInt(), 0 );
     }
 
     void eval_feature_id()