lint: in _Generic expressions, only evaluate the matching branches

Author: rillig

tests/usr.bin/xlint/lint1/c11_generic_expression.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: c11_generic_expression.c,v 1.25 2026/03/16 20:09:15 rillig Exp $	*/
+/*	$NetBSD: c11_generic_expression.c,v 1.26 2026/03/18 06:17:55 rillig Exp $	*/
 # 3 "c11_generic_expression.c"
 
 /* lint1-extra-flags: -X 351 */
@@ -100,7 +100,7 @@ primary_expression(void)
 }
 
 /*
- * The types don't match, therefore build_generic_selection returns NULL,
+ * The types don't match, therefore the _Generic selection evaluates to NULL,
  * which is then silently ignored by init_expr.  This situation is already
  * covered by the compilers, so there is no need for lint to double-check it.
  */
@@ -143,17 +143,53 @@ skip_blank(const char *p)
 {
 	static const unsigned short *_ctype_tab_;
 
-	while (
-		// TODO: In a _Generic expression, only evaluate the
-		//  result expression, but not the others. Only parse
-		//  the others, don't determine their type.
-		_Generic(
-			*p + 1 / 0,
-			/* expect+1: warning: argument to 'function from <ctype.h>' must be 'unsigned char' or EOF, not 'char' [341] */
-			unsigned char: (_ctype_tab_ + 1)[*p] & 0x0200,
-			/* expect+1: warning: argument to 'function from <ctype.h>' must be 'unsigned char' or EOF, not 'char' [341] */
-			int: (_ctype_tab_ + 1)[*p] & 0x0200
-		)
-	)
+	while (_Generic(
+	    p[1 / 0],
+	    unsigned char: (_ctype_tab_ + 1)[*p] & 0x0200,
+	    int: (_ctype_tab_ + 1)[*p] & 0x0200
+	))
 		p++;
 }
+
+const char *
+evaluation_mode(void)
+{
+	return _Generic(
+	    0,
+
+	    // Only parse since 'double' does not match 'int'.
+	    double: 1 / 0,
+
+	    int: "matched",
+
+	    // Only parse since 'const char *' does not match 'int'.
+	    const char *: 1 / 0,
+
+	    // Only parse since a previous branch already matched,
+	    // so the fallback branch is not used.
+	    default: 1 / 0
+	);
+}
+
+const char *
+evaluation_mode_early_default(void)
+{
+	return _Generic(
+	    0,
+
+	    // Lint decides at parse time whether it fully evaluates the
+	    // branch or only parses it. Since the default branch comes
+	    // first, it is not yet known whether any of the other branches
+	    // will match, so evaluate it.
+	    /* expect+1: error: division by 0 [139] */
+	    default: 1 / 0,
+
+	    // Only parse since 'double' does not match 'int'.
+	    double: 1 / 0,
+
+	    int: "matched",
+
+	    // Only parse since 'const char *' does not match 'int'.
+	    const char *: 1 / 0
+	);
+}

usr.bin/xlint/lint1/cgram.y

@@ -1,5 +1,5 @@
 %{
-/* $NetBSD: cgram.y,v 1.537 2026/03/16 20:09:15 rillig Exp $ */
+/* $NetBSD: cgram.y,v 1.538 2026/03/18 06:17:55 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -35,7 +35,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID)
-__RCSID("$NetBSD: cgram.y,v 1.537 2026/03/16 20:09:15 rillig Exp $");
+__RCSID("$NetBSD: cgram.y,v 1.538 2026/03/18 06:17:55 rillig Exp $");
 #endif
 
 #include <limits.h>
@@ -148,6 +148,15 @@ new_attribute(const sbuf_t *prefix, const sbuf_t *name,
 	return attr;
 }
 
+static tnode_t *
+unconst_tnode(const tnode_t *p)
+{
+	void *r;
+
+	memcpy(&r, &p, sizeof(r));
+	return r;
+}
+
 #if YYDEBUG && YYBYACC
 #define YYSTYPE_TOSTRING cgram_to_string
 #endif
@@ -175,7 +184,7 @@ new_attribute(const sbuf_t *prefix, const sbuf_t *name,
 	buffer	*y_string;
 	qual_ptr *y_qual_ptr;
 	bool	y_seen_statement;
-	struct generic_association *y_generic;
+	struct generic_selection y_generic_selection;
 	array_size y_array_size;
 	bool	y_in_system_header;
 	designation y_designation;
@@ -238,7 +247,7 @@ new_attribute(const sbuf_t *prefix, const sbuf_t *name,
 	fprintf(yyo, "%s *", type_qualifiers_string($$->qualifiers));
 } <y_qual_ptr>
 %printer { fprintf(yyo, "%s", $$ ? "yes" : "no"); } <y_seen_statement>
-%printer { fprintf(yyo, "%s", type_name($$->ga_arg)); } <y_generic>
+%printer { fprintf(yyo, "%s", type_name($$.expr_type)); } <y_generic_selection>
 %printer { fprintf(yyo, "%d", $$.dim); } <y_array_size>
 %printer { fprintf(yyo, "%s", $$ ? "yes" : "no"); } <y_in_system_header>
 %printer {
@@ -354,8 +363,7 @@ new_attribute(const sbuf_t *prefix, const sbuf_t *name,
 %type	<y_tnode>	primary_expression
 %type	<y_designation>	member_designator
 %type	<y_tnode>	generic_selection
-%type	<y_generic>	generic_assoc_list
-%type	<y_generic>	generic_association
+%type	<y_generic_selection>	generic_inner
 %type	<y_tnode>	postfix_expression
 %type	<y_tnode>	gcc_statement_expr_list
 %type	<y_tnode>	gcc_statement_expr_item
@@ -605,37 +613,46 @@ member_designator:
 
 /* K&R ---, C90 ---, C99 ---, C11 6.5.1.1, C23 6.5.2.1 */
 generic_selection:
-	T_GENERIC T_LPAREN {
-		push_evaluation_mode(EM_TYPE);
-	} assignment_expression {
-		pop_evaluation_mode();
-	} T_COMMA generic_assoc_list T_RPAREN {
+	T_GENERIC {
 		/* generic selection requires C11 or later */
 		c11ism(345);
-		$$ = build_generic_selection($4, $7);
+	} T_LPAREN generic_inner T_RPAREN {
+		$$ = $4.matched != NULL ? $4.matched : $4.fallback;
 	}
 ;
 
-/* K&R ---, C90 ---, C99 ---, C11 6.5.1.1, C23 6.5.2.1 */
-generic_assoc_list:
-	generic_association
-|	generic_assoc_list T_COMMA generic_association {
-		$3->ga_prev = $1;
-		$$ = $3;
-	}
-;
+/* The rule 'generic_assoc_list' is inlined into 'generic_inner'. */
+/* The rule 'generic_association' is inlined into 'generic_inner'. */
 
-/* K&R ---, C90 ---, C99 ---, C11 6.5.1.1, C23 6.5.2.1 */
-generic_association:
-	type_name T_COLON assignment_expression {
-		$$ = block_zero_alloc(sizeof(*$$), "generic");
-		$$->ga_arg = $1;
-		$$->ga_result = $3;
-	}
-|	T_DEFAULT T_COLON assignment_expression {
-		$$ = block_zero_alloc(sizeof(*$$), "generic");
-		$$->ga_arg = NULL;
-		$$->ga_result = $3;
+generic_inner:
+	{
+		push_evaluation_mode(EM_TYPE);
+	} assignment_expression {
+		pop_evaluation_mode();
+	} {
+		$$ = (struct generic_selection){
+			/* C23 6.5.2.1p2 */
+			.expr_type = $2 != NULL
+			    ? cconv(unconst_tnode($2))->tn_type
+			    : NULL
+		};
+	}
+|	generic_inner T_COMMA type_name T_COLON {
+		$1.assoc_matched = $1.expr_type != NULL && $3 != NULL
+		    && types_compatible($1.expr_type, $3, true, false, NULL);
+		push_evaluation_mode($1.assoc_matched ? EM_EVAL : EM_PARSE);
+	} assignment_expression {
+		pop_evaluation_mode();
+		$$ = $1;
+		if ($$.assoc_matched)
+			$$.matched = $6;
+	}
+|	generic_inner T_COMMA T_DEFAULT T_COLON {
+		push_evaluation_mode($1.matched != NULL ? EM_PARSE : EM_EVAL);
+	} assignment_expression {
+		pop_evaluation_mode();
+		$$ = $1;
+		$$.fallback = $6;
 	}
 ;
 

usr.bin/xlint/lint1/ckctype.c

@@ -1,4 +1,4 @@
-/* $NetBSD: ckctype.c,v 1.13 2024/12/18 18:14:54 rillig Exp $ */
+/* $NetBSD: ckctype.c,v 1.14 2026/03/18 06:17:55 rillig Exp $ */
 
 /*-
  * Copyright (c) 2021 The NetBSD Foundation, Inc.
@@ -36,7 +36,7 @@
 #include <sys/cdefs.h>
 
 #if defined(__RCSID)
-__RCSID("$NetBSD: ckctype.c,v 1.13 2024/12/18 18:14:54 rillig Exp $");
+__RCSID("$NetBSD: ckctype.c,v 1.14 2026/03/18 06:17:55 rillig Exp $");
 #endif
 
 #include <string.h>
@@ -125,7 +125,8 @@ check_ctype_function_call(const function_call *call)
 
 	if (call->args_len == 1 &&
 	    call->func->tn_op == NAME &&
-	    is_ctype_function(call->func->u.sym->s_name))
+	    is_ctype_function(call->func->u.sym->s_name) &&
+	    is_evaluation_mode(EM_TYPE))
 		check_ctype_arg(call->func->u.sym->s_name, call->args[0]);
 }
 
@@ -138,6 +139,7 @@ check_ctype_macro_invocation(const tnode_t *ln, const tnode_t *rn)
 	    ln->u.ops.left->tn_op == LOAD &&
 	    ln->u.ops.left->u.ops.left != NULL &&
 	    ln->u.ops.left->u.ops.left->tn_op == NAME &&
-	    is_ctype_table(ln->u.ops.left->u.ops.left->u.sym->s_name))
+	    is_ctype_table(ln->u.ops.left->u.ops.left->u.sym->s_name) &&
+	    is_evaluation_mode(EM_TYPE))
 		check_ctype_arg("function from <ctype.h>", rn);
 }

usr.bin/xlint/lint1/externs1.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: externs1.h,v 1.244 2026/03/15 07:55:59 rillig Exp $	*/
+/*	$NetBSD: externs1.h,v 1.245 2026/03/18 06:17:55 rillig Exp $	*/
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -286,8 +286,6 @@ bool is_compiler_builtin(const char *);
 tnode_t *build_constant(type_t *, val_t *);
 tnode_t *build_name(sym_t *, bool);
 tnode_t *build_string(buffer *);
-tnode_t *build_generic_selection(const tnode_t *,
-		    struct generic_association *);
 
 tnode_t *build_binary(tnode_t *, op_t, bool, tnode_t *);
 tnode_t *build_unary(op_t, bool, tnode_t *);

usr.bin/xlint/lint1/lint1.h

@@ -1,4 +1,4 @@
-/* $NetBSD: lint1.h,v 1.239 2026/03/15 07:55:59 rillig Exp $ */
+/* $NetBSD: lint1.h,v 1.240 2026/03/18 06:17:55 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -329,10 +329,11 @@ struct tnode {
 	} u;
 };
 
-struct generic_association {
-	type_t *ga_arg;		/* NULL means default or error */
-	tnode_t *ga_result;	/* NULL means error */
-	struct generic_association *ga_prev;
+struct generic_selection {
+	const type_t *expr_type;
+	tnode_t *fallback;
+	tnode_t *matched;
+	bool assoc_matched;
 };
 
 typedef struct {

usr.bin/xlint/lint1/tree.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: tree.c,v 1.703 2026/03/15 07:56:00 rillig Exp $	*/
+/*	$NetBSD: tree.c,v 1.704 2026/03/18 06:17:55 rillig Exp $	*/
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID)
-__RCSID("$NetBSD: tree.c,v 1.703 2026/03/15 07:56:00 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.704 2026/03/18 06:17:55 rillig Exp $");
 #endif
 
 #include <float.h>
@@ -949,35 +949,6 @@ build_string(buffer *lit)
 	return n;
 }
 
-static tnode_t *
-unconst_tnode(const tnode_t *p)
-{
-	void *r;
-
-	memcpy(&r, &p, sizeof(r));
-	return r;
-}
-
-tnode_t *
-build_generic_selection(const tnode_t *expr,
-			struct generic_association *sel)
-{
-	tnode_t *default_result = NULL;
-
-	if (expr != NULL)
-		expr = cconv(unconst_tnode(expr));	/* C23 6.5.2.1p2 */
-
-	for (; sel != NULL; sel = sel->ga_prev) {
-		if (expr != NULL &&
-		    types_compatible(sel->ga_arg, expr->tn_type,
-			true, false, NULL))
-			return sel->ga_result;
-		if (sel->ga_arg == NULL)
-			default_result = sel->ga_result;
-	}
-	return default_result;
-}
-
 static bool
 is_out_of_char_range(const tnode_t *tn)
 {