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/* Implementation of -Wmisleading-indentation
Copyright (C) 2015-2021 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "c-common.h"
#include "c-indentation.h"
#include "selftest.h"
#include "diagnostic.h"
/* Round up VIS_COLUMN to nearest tab stop. */
static unsigned int
next_tab_stop (unsigned int vis_column, unsigned int tab_width)
{
vis_column = ((vis_column + tab_width) / tab_width) * tab_width;
return vis_column;
}
/* Convert libcpp's notion of a column (a 1-based char count) to
the "visual column" (0-based column, respecting tabs), by reading the
relevant line.
Returns true if a conversion was possible, writing the result to OUT,
otherwise returns false. If FIRST_NWS is not NULL, then write to it
the visual column corresponding to the first non-whitespace character
on the line (up to or before EXPLOC). */
static bool
get_visual_column (expanded_location exploc,
unsigned int *out,
unsigned int *first_nws,
unsigned int tab_width)
{
char_span line = location_get_source_line (exploc.file, exploc.line);
if (!line)
return false;
if ((size_t)exploc.column > line.length ())
return false;
unsigned int vis_column = 0;
for (int i = 1; i < exploc.column; i++)
{
unsigned char ch = line[i - 1];
if (first_nws != NULL && !ISSPACE (ch))
{
*first_nws = vis_column;
first_nws = NULL;
}
if (ch == '\t')
vis_column = next_tab_stop (vis_column, tab_width);
else
vis_column++;
}
if (first_nws != NULL)
*first_nws = vis_column;
*out = vis_column;
return true;
}
/* Attempt to determine the first non-whitespace character in line LINE_NUM
of source line FILE.
If this is possible, return true and write its "visual column" to
*FIRST_NWS.
Otherwise, return false, leaving *FIRST_NWS untouched. */
static bool
get_first_nws_vis_column (const char *file, int line_num,
unsigned int *first_nws,
unsigned int tab_width)
{
gcc_assert (first_nws);
char_span line = location_get_source_line (file, line_num);
if (!line)
return false;
unsigned int vis_column = 0;
for (size_t i = 1; i < line.length (); i++)
{
unsigned char ch = line[i - 1];
if (!ISSPACE (ch))
{
*first_nws = vis_column;
return true;
}
if (ch == '\t')
vis_column = next_tab_stop (vis_column, tab_width);
else
vis_column++;
}
/* No non-whitespace characters found. */
return false;
}
/* Determine if there is an unindent/outdent between
BODY_EXPLOC and NEXT_STMT_EXPLOC, to ensure that we don't
issue a warning for cases like the following:
(1) Preprocessor logic
if (flagA)
foo ();
^ BODY_EXPLOC
#if SOME_CONDITION_THAT_DOES_NOT_HOLD
if (flagB)
#endif
bar ();
^ NEXT_STMT_EXPLOC
"bar ();" is visually aligned below "foo ();" and
is (as far as the parser sees) the next token, but
this isn't misleading to a human reader.
(2) Empty macro with bad indentation
In the following, the
"if (i > 0)"
is poorly indented, and ought to be on the same column as
"engine_ref_debug(e, 0, -1)"
However, it is not misleadingly indented, due to the presence
of that macro.
#define engine_ref_debug(X, Y, Z)
if (locked)
i = foo (0);
else
i = foo (1);
engine_ref_debug(e, 0, -1)
if (i > 0)
return 1;
Return true if such an unindent/outdent is detected. */
static bool
detect_intervening_unindent (const char *file,
int body_line,
int next_stmt_line,
unsigned int vis_column,
unsigned int tab_width)
{
gcc_assert (file);
gcc_assert (next_stmt_line > body_line);
for (int line = body_line + 1; line < next_stmt_line; line++)
{
unsigned int line_vis_column;
if (get_first_nws_vis_column (file, line, &line_vis_column, tab_width))
if (line_vis_column < vis_column)
return true;
}
/* Not found. */
return false;
}
/* Helper function for warn_for_misleading_indentation; see
description of that function below. */
static bool
should_warn_for_misleading_indentation (const token_indent_info &guard_tinfo,
const token_indent_info &body_tinfo,
const token_indent_info &next_tinfo)
{
/* Don't attempt to compare indentation if #line or # 44 "file"-style
directives are present, suggesting generated code.
All bets are off if these are present: the file that the #line
directive could have an entirely different coding layout to C/C++
(e.g. .md files).
To determine if a #line is present, in theory we could look for a
map with reason == LC_RENAME_VERBATIM. However, if there has
subsequently been a long line requiring a column number larger than
that representable by the original LC_RENAME_VERBATIM map, then
we'll have a map with reason LC_RENAME.
Rather than attempting to search all of the maps for a
LC_RENAME_VERBATIM, instead we have libcpp set a flag whenever one
is seen, and we check for the flag here.
*/
if (line_table->seen_line_directive)
return false;
/* We can't usefully warn about do-while and switch statements since the
bodies of these statements are always explicitly delimited at both ends,
so control flow is quite obvious. */
if (guard_tinfo.keyword == RID_DO
|| guard_tinfo.keyword == RID_SWITCH)
return false;
/* If the token following the body is a close brace or an "else"
then while indentation may be sloppy, there is not much ambiguity
about control flow, e.g.
if (foo) <- GUARD
bar (); <- BODY
else baz (); <- NEXT
{
while (foo) <- GUARD
bar (); <- BODY
} <- NEXT
baz ();
*/
enum cpp_ttype next_tok_type = next_tinfo.type;
if (next_tok_type == CPP_CLOSE_BRACE
|| next_tinfo.keyword == RID_ELSE)
return false;
/* Likewise, if the body of the guard is a compound statement then control
flow is quite visually explicit regardless of the code's possibly poor
indentation, e.g.
while (foo) <- GUARD
{ <- BODY
bar ();
}
baz (); <- NEXT
Things only get muddy when the body of the guard does not have
braces, e.g.
if (foo) <- GUARD
bar (); <- BODY
baz (); <- NEXT
*/
enum cpp_ttype body_type = body_tinfo.type;
if (body_type == CPP_OPEN_BRACE)
return false;
/* Don't warn here about spurious semicolons. */
if (next_tok_type == CPP_SEMICOLON)
return false;
location_t guard_loc = guard_tinfo.location;
location_t body_loc = body_tinfo.location;
location_t next_stmt_loc = next_tinfo.location;
/* Resolve each token location to the respective macro expansion
point that produced the token. */
if (linemap_location_from_macro_expansion_p (line_table, guard_loc))
guard_loc = linemap_resolve_location (line_table, guard_loc,
LRK_MACRO_EXPANSION_POINT, NULL);
if (linemap_location_from_macro_expansion_p (line_table, body_loc))
body_loc = linemap_resolve_location (line_table, body_loc,
LRK_MACRO_EXPANSION_POINT, NULL);
if (linemap_location_from_macro_expansion_p (line_table, next_stmt_loc))
next_stmt_loc = linemap_resolve_location (line_table, next_stmt_loc,
LRK_MACRO_EXPANSION_POINT, NULL);
/* When all three tokens are produced from a single macro expansion, we
instead consider their loci inside that macro's definition. */
if (guard_loc == body_loc && body_loc == next_stmt_loc)
{
const line_map *guard_body_common_map
= first_map_in_common (line_table,
guard_tinfo.location, body_tinfo.location,
&guard_loc, &body_loc);
const line_map *body_next_common_map
= first_map_in_common (line_table,
body_tinfo.location, next_tinfo.location,
&body_loc, &next_stmt_loc);
/* Punt on complicated nesting of macros. */
if (guard_body_common_map != body_next_common_map)
return false;
guard_loc = linemap_resolve_location (line_table, guard_loc,
LRK_MACRO_DEFINITION_LOCATION, NULL);
body_loc = linemap_resolve_location (line_table, body_loc,
LRK_MACRO_DEFINITION_LOCATION, NULL);
next_stmt_loc = linemap_resolve_location (line_table, next_stmt_loc,
LRK_MACRO_DEFINITION_LOCATION,
NULL);
}
expanded_location body_exploc = expand_location (body_loc);
expanded_location next_stmt_exploc = expand_location (next_stmt_loc);
expanded_location guard_exploc = expand_location (guard_loc);
/* PR c++/68819: if the column number is zero, we presumably
had a location_t > LINE_MAP_MAX_LOCATION_WITH_COLS, and so
we have no column information. */
if (!guard_exploc.column || !body_exploc.column || !next_stmt_exploc.column)
{
static bool issued_note = false;
if (!issued_note)
{
/* Notify the user the first time this happens. */
issued_note = true;
inform (guard_loc,
"%<-Wmisleading-indentation%> is disabled from this point"
" onwards, since column-tracking was disabled due to"
" the size of the code/headers");
if (!flag_large_source_files)
inform (guard_loc,
"adding %<-flarge-source-files%> will allow for more"
" column-tracking support, at the expense of compilation"
" time and memory");
}
return false;
}
/* Give up if the loci are not all distinct. */
if (guard_loc == body_loc || body_loc == next_stmt_loc)
return false;
const unsigned int tab_width = global_dc->tabstop;
/* They must be in the same file. */
if (next_stmt_exploc.file != body_exploc.file)
return false;
/* If NEXT_STMT_LOC and BODY_LOC are on the same line, consider
the location of the guard.
Cases where we want to issue a warning:
if (flag)
foo (); bar ();
^ WARN HERE
if (flag) foo (); bar ();
^ WARN HERE
if (flag) ; {
^ WARN HERE
if (flag)
; {
^ WARN HERE
Cases where we don't want to issue a warning:
various_code (); if (flag) foo (); bar (); more_code ();
^ DON'T WARN HERE. */
if (next_stmt_exploc.line == body_exploc.line)
{
if (guard_exploc.file != body_exploc.file)
return true;
if (guard_exploc.line < body_exploc.line)
/* The guard is on a line before a line that contains both
the body and the next stmt. */
return true;
else if (guard_exploc.line == body_exploc.line)
{
/* They're all on the same line. */
gcc_assert (guard_exploc.file == next_stmt_exploc.file);
gcc_assert (guard_exploc.line == next_stmt_exploc.line);
unsigned int guard_vis_column;
unsigned int guard_line_first_nws;
if (!get_visual_column (guard_exploc,
&guard_vis_column,
&guard_line_first_nws, tab_width))
return false;
/* Heuristic: only warn if the guard is the first thing
on its line. */
if (guard_vis_column == guard_line_first_nws)
return true;
}
}
/* If NEXT_STMT_LOC is on a line after BODY_LOC, consider
their relative locations, and of the guard.
Cases where we want to issue a warning:
if (flag)
foo ();
bar ();
^ WARN HERE
Cases where we don't want to issue a warning:
if (flag)
foo ();
bar ();
^ DON'T WARN HERE (autogenerated code?)
if (flagA)
foo ();
#if SOME_CONDITION_THAT_DOES_NOT_HOLD
if (flagB)
#endif
bar ();
^ DON'T WARN HERE
if (flag)
;
foo ();
^ DON'T WARN HERE
#define emit
if (flag)
foo ();
emit bar ();
^ DON'T WARN HERE
*/
if (next_stmt_exploc.line > body_exploc.line)
{
/* Determine if GUARD_LOC and NEXT_STMT_LOC are aligned on the same
"visual column"... */
unsigned int next_stmt_vis_column;
unsigned int next_stmt_line_first_nws;
unsigned int body_vis_column;
unsigned int body_line_first_nws;
unsigned int guard_vis_column;
unsigned int guard_line_first_nws;
/* If we can't determine it, don't issue a warning. This is sometimes
the case for input files containing #line directives, and these
are often for autogenerated sources (e.g. from .md files), where
it's not clear that it's meaningful to look at indentation. */
if (!get_visual_column (next_stmt_exploc,
&next_stmt_vis_column,
&next_stmt_line_first_nws, tab_width))
return false;
if (!get_visual_column (body_exploc,
&body_vis_column,
&body_line_first_nws, tab_width))
return false;
if (!get_visual_column (guard_exploc,
&guard_vis_column,
&guard_line_first_nws, tab_width))
return false;
/* If the line where the next stmt starts has non-whitespace
on it before the stmt, then don't warn:
#define emit
if (flag)
foo ();
emit bar ();
^ DON'T WARN HERE
(PR c/69122). */
if (next_stmt_line_first_nws < next_stmt_vis_column)
return false;
if ((body_type != CPP_SEMICOLON
&& next_stmt_vis_column == body_vis_column)
/* As a special case handle the case where the body is a semicolon
that may be hidden by a preceding comment, e.g. */
// if (p)
// /* blah */;
// foo (1);
/* by looking instead at the column of the first non-whitespace
character on the body line. */
|| (body_type == CPP_SEMICOLON
&& body_exploc.line > guard_exploc.line
&& body_line_first_nws != body_vis_column
&& next_stmt_vis_column > guard_line_first_nws))
{
/* Don't warn if they are aligned on the same column
as the guard itself (suggesting autogenerated code that doesn't
bother indenting at all).
For "else" clauses, we consider the column of the first
non-whitespace character on the guard line instead of the column
of the actual guard token itself because it is more sensible.
Consider:
if (p) {
foo (1);
} else // GUARD
foo (2); // BODY
foo (3); // NEXT
and:
if (p)
foo (1);
} else // GUARD
foo (2); // BODY
foo (3); // NEXT
If we just used the column of the "else" token, we would warn on
the first example and not warn on the second. But we want the
exact opposite to happen: to not warn on the first example (which
is probably autogenerated) and to warn on the second (whose
indentation is misleading). Using the column of the first
non-whitespace character on the guard line makes that
happen. */
unsigned int guard_column = (guard_tinfo.keyword == RID_ELSE
? guard_line_first_nws
: guard_vis_column);
if (guard_column == body_vis_column)
return false;
/* We may have something like:
if (p)
{
foo (1);
} else // GUARD
foo (2); // BODY
foo (3); // NEXT
in which case the columns are not aligned but the code is not
misleadingly indented. If the column of the body isn't indented
more than the guard line then don't warn. */
if (body_vis_column <= guard_line_first_nws)
return false;
/* Don't warn if there is an unindent between the two statements. */
int vis_column = MIN (next_stmt_vis_column, body_vis_column);
if (detect_intervening_unindent (body_exploc.file, body_exploc.line,
next_stmt_exploc.line,
vis_column, tab_width))
return false;
/* Otherwise, they are visually aligned: issue a warning. */
return true;
}
/* Also issue a warning for code having the form:
if (flag);
foo ();
while (flag);
{
...
}
for (...);
{
...
}
if (flag)
;
else if (flag);
foo ();
where the semicolon at the end of each guard is most likely spurious.
But do not warn on:
for (..);
foo ();
where the next statement is aligned with the guard.
*/
if (body_type == CPP_SEMICOLON)
{
if (body_exploc.line == guard_exploc.line)
{
if (next_stmt_vis_column > guard_line_first_nws
|| (next_tok_type == CPP_OPEN_BRACE
&& next_stmt_vis_column == guard_line_first_nws))
return true;
}
}
}
return false;
}
/* Return the string identifier corresponding to the given guard token. */
const char *
guard_tinfo_to_string (enum rid keyword)
{
switch (keyword)
{
case RID_FOR:
return "for";
case RID_ELSE:
return "else";
case RID_IF:
return "if";
case RID_WHILE:
return "while";
case RID_DO:
return "do";
case RID_SWITCH:
return "switch";
default:
gcc_unreachable ();
}
}
/* Called by the C/C++ frontends when we have a guarding statement at
GUARD_LOC containing a statement at BODY_LOC, where the block wasn't
written using braces, like this:
if (flag)
foo ();
along with the location of the next token, at NEXT_STMT_LOC,
so that we can detect followup statements that are within
the same "visual block" as the guarded statement, but which
aren't logically grouped within the guarding statement, such
as:
GUARD_LOC
|
V
if (flag)
foo (); <- BODY_LOC
bar (); <- NEXT_STMT_LOC
In the above, "bar ();" isn't guarded by the "if", but
is indented to misleadingly suggest that it is in the same
block as "foo ();".
GUARD_KIND identifies the kind of clause e.g. "if", "else" etc. */
void
warn_for_misleading_indentation (const token_indent_info &guard_tinfo,
const token_indent_info &body_tinfo,
const token_indent_info &next_tinfo)
{
/* Early reject for the case where -Wmisleading-indentation is disabled,
to avoid doing work only to have the warning suppressed inside the
diagnostic machinery. */
if (!warn_misleading_indentation)
return;
if (should_warn_for_misleading_indentation (guard_tinfo,
body_tinfo,
next_tinfo))
{
auto_diagnostic_group d;
if (warning_at (guard_tinfo.location, OPT_Wmisleading_indentation,
"this %qs clause does not guard...",
guard_tinfo_to_string (guard_tinfo.keyword)))
inform (next_tinfo.location,
"...this statement, but the latter is misleadingly indented"
" as if it were guarded by the %qs",
guard_tinfo_to_string (guard_tinfo.keyword));
}
}
#if CHECKING_P
namespace selftest {
/* Verify that next_tab_stop works as expected. */
static void
test_next_tab_stop ()
{
const unsigned int tab_width = 8;
ASSERT_EQ (next_tab_stop (0, tab_width), 8);
ASSERT_EQ (next_tab_stop (1, tab_width), 8);
ASSERT_EQ (next_tab_stop (7, tab_width), 8);
ASSERT_EQ (next_tab_stop (8, tab_width), 16);
ASSERT_EQ (next_tab_stop (9, tab_width), 16);
ASSERT_EQ (next_tab_stop (15, tab_width), 16);
ASSERT_EQ (next_tab_stop (16, tab_width), 24);
ASSERT_EQ (next_tab_stop (17, tab_width), 24);
ASSERT_EQ (next_tab_stop (23, tab_width), 24);
}
/* Verify that the given call to get_visual_column succeeds, with
the given results. */
static void
assert_get_visual_column_succeeds (const location &loc,
const char *file, int line, int column,
const unsigned int tab_width,
unsigned int expected_visual_column,
unsigned int expected_first_nws)
{
expanded_location exploc;
exploc.file = file;
exploc.line = line;
exploc.column = column;
exploc.data = NULL;
exploc.sysp = false;
unsigned int actual_visual_column;
unsigned int actual_first_nws;
bool result = get_visual_column (exploc,
&actual_visual_column,
&actual_first_nws, tab_width);
ASSERT_TRUE_AT (loc, result);
ASSERT_EQ_AT (loc, actual_visual_column, expected_visual_column);
ASSERT_EQ_AT (loc, actual_first_nws, expected_first_nws);
}
/* Verify that the given call to get_visual_column succeeds, with
the given results. */
#define ASSERT_GET_VISUAL_COLUMN_SUCCEEDS(FILENAME, LINE, COLUMN, \
TAB_WIDTH, \
EXPECTED_VISUAL_COLUMN, \
EXPECTED_FIRST_NWS) \
SELFTEST_BEGIN_STMT \
assert_get_visual_column_succeeds (SELFTEST_LOCATION, \
FILENAME, LINE, COLUMN, \
TAB_WIDTH, \
EXPECTED_VISUAL_COLUMN, \
EXPECTED_FIRST_NWS); \
SELFTEST_END_STMT
/* Verify that the given call to get_visual_column fails gracefully. */
static void
assert_get_visual_column_fails (const location &loc,
const char *file, int line, int column,
const unsigned int tab_width)
{
expanded_location exploc;
exploc.file = file;
exploc.line = line;
exploc.column = column;
exploc.data = NULL;
exploc.sysp = false;
unsigned int actual_visual_column;
unsigned int actual_first_nws;
bool result = get_visual_column (exploc,
&actual_visual_column,
&actual_first_nws, tab_width);
ASSERT_FALSE_AT (loc, result);
}
/* Verify that the given call to get_visual_column fails gracefully. */
#define ASSERT_GET_VISUAL_COLUMN_FAILS(FILENAME, LINE, COLUMN, \
TAB_WIDTH) \
SELFTEST_BEGIN_STMT \
assert_get_visual_column_fails (SELFTEST_LOCATION, \
FILENAME, LINE, COLUMN, \
TAB_WIDTH); \
SELFTEST_END_STMT
/* Verify that get_visual_column works as expected. */
static void
test_get_visual_column ()
{
/* Create a tempfile with a mixture of tabs and spaces.
Both lines have either a space or a tab, then " line N",
for 8 characters in total.
1-based "columns" (w.r.t. to line 1):
.....................0000000001111.
.....................1234567890123. */
const char *content = (" line 1\n"
"\t line 2\n");
line_table_test ltt;
temp_source_file tmp (SELFTEST_LOCATION, ".txt", content);
const unsigned int tab_width = 8;
const char *file = tmp.get_filename ();
/* Line 1 (space-based indentation). */
{
const int line = 1;
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 1, tab_width, 0, 0);
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 2, tab_width, 1, 1);
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 3, tab_width, 2, 2);
/* first_nws should have stopped increasing. */
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 4, tab_width, 3, 2);
/* Verify the end-of-line boundary. */
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 8, tab_width, 7, 2);
ASSERT_GET_VISUAL_COLUMN_FAILS (file, line, 9, tab_width);
}
/* Line 2 (tab-based indentation). */
{
const int line = 2;
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 1, tab_width, 0, 0);
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 2, tab_width, 8, 8);
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 3, tab_width, 9, 9);
/* first_nws should have stopped increasing. */
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 4, tab_width, 10, 9);
/* Verify the end-of-line boundary. */
ASSERT_GET_VISUAL_COLUMN_SUCCEEDS (file, line, 8, tab_width, 14, 9);
ASSERT_GET_VISUAL_COLUMN_FAILS (file, line, 9, tab_width);
}
}
/* Run all of the selftests within this file. */
void
c_indentation_c_tests ()
{
test_next_tab_stop ();
test_get_visual_column ();
}
} // namespace selftest
#endif /* CHECKING_P */