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c.opt (Wdangling-else): New option.

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* c.opt (Wdangling-else): New option.

	* c-parser.c (c_parser_if_statement): Replace OPT_Wparentheses with
	OPT_Wdangling_else.

	* parser.c (cp_parser_selection_statement): Replace OPT_Wparentheses
	with OPT_Wdangling_else.

	* doc/invoke.texi: Document -Wdangling-else.

	* c-c++-common/Wdangling-else-1.c: New test.
	* c-c++-common/Wdangling-else-2.c: New test.
	* c-c++-common/Wdangling-else-3.c: New test.

From-SVN: r235885
This commit is contained in:
Marek Polacek 2016-05-04 16:00:33 +00:00 committed by Marek Polacek
parent 5396db971e
commit deef711327
12 changed files with 116 additions and 43 deletions
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4
gcc/ChangeLog
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@ -1,3 +1,7 @@
2016-05-04 Marek Polacek <polacek@redhat.com>
* doc/invoke.texi: Document -Wdangling-else.
2016-05-04 Thomas Preud'homme <thomas.preudhomme@arm.com>
* config.gcc: Error out when conflicting multilib is detected. Do not

4
gcc/c-family/ChangeLog
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@ -1,3 +1,7 @@
2016-05-04 Marek Polacek <polacek@redhat.com>
* c.opt (Wdangling-else): New option.
2016-05-03 Marek Polacek <polacek@redhat.com>
PR c/70859

4
gcc/c-family/c.opt
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@ -370,6 +370,10 @@ Wctor-dtor-privacy
C++ ObjC++ Var(warn_ctor_dtor_privacy) Warning
Warn when all constructors and destructors are private.
Wdangling-else
C ObjC C++ ObjC++ Var(warn_dangling_else) Warning LangEnabledBy(C ObjC C++ ObjC++,Wparentheses)
Warn about dangling else.
Wdate-time
C ObjC C++ ObjC++ CPP(warn_date_time) CppReason(CPP_W_DATE_TIME) Var(cpp_warn_date_time) Init(0) Warning
Warn about __TIME__, __DATE__ and __TIMESTAMP__ usage.

5
gcc/c/ChangeLog
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@ -1,3 +1,8 @@
2016-05-04 Marek Polacek <polacek@redhat.com>
* c-parser.c (c_parser_if_statement): Replace OPT_Wparentheses with
OPT_Wdangling_else.
2016-05-04 Marek Polacek <polacek@redhat.com>
PR c/48778

2
gcc/c/c-parser.c
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@ -5542,7 +5542,7 @@ c_parser_if_statement (c_parser *parser, bool *if_p, vec<tree> *chain)
/* Diagnose an ambiguous else if if-then-else is nested inside
if-then. */
if (nested_if)
warning_at (loc, OPT_Wparentheses,
warning_at (loc, OPT_Wdangling_else,
"suggest explicit braces to avoid ambiguous %<else%>");
if (warn_duplicated_cond)

5
gcc/cp/ChangeLog
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@ -1,3 +1,8 @@
2016-05-04 Marek Polacek <polacek@redhat.com>
* parser.c (cp_parser_selection_statement): Replace OPT_Wparentheses
with OPT_Wdangling_else.
2016-05-03 Martin Sebor <msebor@redhat.com>
PR c++/66561

2
gcc/cp/parser.c
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@ -10951,7 +10951,7 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
statement which does have an else clause. We warn
about the potential ambiguity. */
if (nested_if)
warning_at (EXPR_LOCATION (statement), OPT_Wparentheses,
warning_at (EXPR_LOCATION (statement), OPT_Wdangling_else,
"suggest explicit braces to avoid ambiguous"
" %<else%>");
if (warn_duplicated_cond)

88
gcc/doc/invoke.texi
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@ -257,7 +257,8 @@ Objective-C and Objective-C++ Dialects}.
-Wc90-c99-compat -Wc99-c11-compat @gol
-Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
-Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported @gol
-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdate-time -Wdelete-incomplete @gol
-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time @gol
-Wdelete-incomplete @gol
-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
-Wdisabled-optimization @gol
-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
@ -3976,46 +3977,6 @@ Also warn if a comparison like @code{x<=y<=z} appears; this is
equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different
interpretation from that of ordinary mathematical notation.
Also warn about constructions where there may be confusion to which
@code{if} statement an @code{else} branch belongs. Here is an example of
such a case:
@smallexample
@group
@{
if (a)
if (b)
foo ();
else
bar ();
@}
@end group
@end smallexample
In C/C++, every @code{else} branch belongs to the innermost possible
@code{if} statement, which in this example is @code{if (b)}. This is
often not what the programmer expected, as illustrated in the above
example by indentation the programmer chose. When there is the
potential for this confusion, GCC issues a warning when this flag
is specified. To eliminate the warning, add explicit braces around
the innermost @code{if} statement so there is no way the @code{else}
can belong to the enclosing @code{if}. The resulting code
looks like this:
@smallexample
@group
@{
if (a)
@{
if (b)
foo ();
else
bar ();
@}
@}
@end group
@end smallexample
Also warn for dangerous uses of the GNU extension to
@code{?:} with omitted middle operand. When the condition
in the @code{?}: operator is a boolean expression, the omitted value is
@ -5148,6 +5109,51 @@ compiler doesn't give this warning for types defined in the main .C
file, as those are unlikely to have multiple definitions.
@option{-Wsubobject-linkage} is enabled by default.
@item -Wdangling-else
@opindex Wdangling-else
@opindex Wno-dangling-else
Warn about constructions where there may be confusion to which
@code{if} statement an @code{else} branch belongs. Here is an example of
such a case:
@smallexample
@group
@{
if (a)
if (b)
foo ();
else
bar ();
@}
@end group
@end smallexample
In C/C++, every @code{else} branch belongs to the innermost possible
@code{if} statement, which in this example is @code{if (b)}. This is
often not what the programmer expected, as illustrated in the above
example by indentation the programmer chose. When there is the
potential for this confusion, GCC issues a warning when this flag
is specified. To eliminate the warning, add explicit braces around
the innermost @code{if} statement so there is no way the @code{else}
can belong to the enclosing @code{if}. The resulting code
looks like this:
@smallexample
@group
@{
if (a)
@{
if (b)
foo ();
else
bar ();
@}
@}
@end group
@end smallexample
This warning is enabled by @option{-Wparentheses}.
@item -Wdate-time
@opindex Wdate-time
@opindex Wno-date-time

6
gcc/testsuite/ChangeLog
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@ -1,3 +1,9 @@
2016-05-04 Marek Polacek <polacek@redhat.com>
* c-c++-common/Wdangling-else-1.c: New test.
* c-c++-common/Wdangling-else-2.c: New test.
* c-c++-common/Wdangling-else-3.c: New test.
2016-05-04 Kwok Cheung Yeung <kcy@codesourcery.com>
* gcc.target/mips/mips16-attributes.c: Skip if -mmicromips

13
gcc/testsuite/c-c++-common/Wdangling-else-1.c Normal file
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@ -0,0 +1,13 @@
/* { dg-do compile } */
/* { dg-options "-Wdangling-else" } */
void bar (int);
void
foo (int a, int b)
{
if (a) /* { dg-warning "suggest explicit braces to avoid ambiguous" } */
if (b)
bar (1);
else
bar (2);
}

13
gcc/testsuite/c-c++-common/Wdangling-else-2.c Normal file
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@ -0,0 +1,13 @@
/* { dg-do compile } */
/* { dg-options "-Wparentheses" } */
void bar (int);
void
foo (int a, int b)
{
if (a) /* { dg-warning "suggest explicit braces to avoid ambiguous" } */
if (b)
bar (1);
else
bar (2);
}

13
gcc/testsuite/c-c++-common/Wdangling-else-3.c Normal file
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@ -0,0 +1,13 @@
/* { dg-do compile } */
/* { dg-options "-Wparentheses -Wno-dangling-else" } */
void bar (int);
void
foo (int a, int b)
{
if (a) /* { dg-bogus "suggest explicit braces to avoid ambiguous" } */
if (b)
bar (1);
else
bar (2);
}