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c11_generic_expression.c revision 1.16 
      1 /*	$NetBSD: c11_generic_expression.c,v 1.16 2023/07/07 00:20:39 rillig Exp $	*/
      2 # 3 "c11_generic_expression.c"
      3 
      4 /*
      5  * C99 added support for type-generic macros, but these were limited to the
      6  * header <tgmath.h>.  C11 made this feature generally available.
      7  *
      8  * The generic selection is typically used with macros, but since lint1 works
      9  * on the preprocessed source, the test cases look a bit strange.
     10  *
     11  * C11 6.5.1.1 "Generic selection"
     12  */
     13 
     14 /* lint1-extra-flags: -Ac11 */
     15 
     16 /*
     17  * The type of 'var' is not compatible with any of the types from the
     18  * generic-association.  This is a compile-time error.
     19  */
     20 const char *
     21 classify_type_without_default(double var)
     22 {
     23 	/* expect-2: warning: argument 'var' unused in function 'classify_type_without_default' [231] */
     24 
     25 	return _Generic(var,
     26 	    long double: "long double",
     27 	    long long: "long long",
     28 	    unsigned: "unsigned"
     29 	);
     30 	/* expect-1: warning: function 'classify_type_without_default' expects to return value [214] */
     31 }
     32 
     33 /*
     34  * In this case, the 'default' expression is selected.
     35  */
     36 const char *
     37 classify_type_with_default(double var)
     38 {
     39 	/* expect-2: warning: argument 'var' unused in function 'classify_type_with_default' [231] */
     40 
     41 	return _Generic(var,
     42 	    long double: "long double",
     43 	    long long: "long long",
     44 	    unsigned: "unsigned",
     45 	    default: "unknown"
     46 	);
     47 }
     48 
     49 /*
     50  * The type of a _Generic expression is the one from the selected association.
     51  */
     52 const char *
     53 classify_char(char c)
     54 {
     55 	/* expect-2: warning: argument 'c' unused in function 'classify_char' [231] */
     56 
     57 	return _Generic(c,
     58 	    char: "yes",
     59 	    default: 0.0
     60 	);
     61 }
     62 
     63 /*
     64  * Before cgram.y 1.238 from 2021-06-27, lint accepted a comma-expression,
     65  * which looked as if _Generic would accept multiple arguments before the
     66  * selection.
     67  */
     68 /* ARGSUSED */
     69 const int *
     70 comma_expression(char first, double second)
     71 {
     72 	/* expect+1: error: syntax error 'second' [249] */
     73 	return _Generic(first, second,
     74 	    char: "first",
     75 	    double: 2.0
     76 	);
     77 	/* expect+1: warning: function 'comma_expression' falls off bottom without returning value [217] */
     78 }
     79 
     80 /*
     81  * Ensure that assignment-expressions are accepted by the grammar, as
     82  * opposed to comma-expressions.
     83  */
     84 /* ARGSUSED */
     85 int
     86 assignment_expression(int first, int second)
     87 {
     88 	return _Generic(first = second,
     89 	    int: second = first
     90 	);
     91 }
     92 
     93 int
     94 primary_expression(void)
     95 {
     96 	return _Generic(0, int: assignment_expression)(0, 0);
     97 }
     98 
     99 /*
    100  * The types don't match, therefore build_generic_selection returns NULL,
    101  * which is then silently ignored by init_expr.  This situation is already
    102  * covered by the compilers, so there is no need for lint to double-check it.
    103  */
    104 /* expect+1: warning: missing 'extern' header declaration for 'x' [351] */
    105 const char *x = _Generic(
    106     1ULL + 1.0f,
    107     int: 1
    108 );
    109