/* Implementation of -Wmisleading-indentation Copyright (C) 2015-2017 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 . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "c-common.h" #include "c-indentation.h" extern cpp_options *cpp_opts; /* Round up VIS_COLUMN to nearest tab stop. */ static unsigned int next_tab_stop (unsigned int vis_column) { const unsigned int tab_width = cpp_opts->tabstop; 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. */ static bool get_visual_column (expanded_location exploc, location_t loc, unsigned int *out, unsigned int *first_nws) { /* 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. Act as if no conversion was possible, triggering the error-handling path in the caller. */ if (!exploc.column) { static bool issued_note = false; if (!issued_note) { /* Notify the user the first time this happens. */ issued_note = true; inform (loc, "-Wmisleading-indentation is disabled from this point" " onwards, since column-tracking was disabled due to" " the size of the code/headers"); } return false; } int line_len; const char *line = location_get_source_line (exploc.file, exploc.line, &line_len); if (!line) 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); 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) { gcc_assert (first_nws); int line_len; const char *line = location_get_source_line (file, line_num, &line_len); if (!line) return false; unsigned int vis_column = 0; for (int i = 1; i < line_len; 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); 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) { 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)) 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) { location_t guard_loc = guard_tinfo.location; location_t body_loc = body_tinfo.location; location_t next_stmt_loc = next_tinfo.location; enum cpp_ttype body_type = body_tinfo.type; enum cpp_ttype next_tok_type = next_tinfo.type; /* Don't attempt to compare the indentation of BODY_LOC and NEXT_STMT_LOC if either are within macros. */ if (linemap_location_from_macro_expansion_p (line_table, body_loc) || linemap_location_from_macro_expansion_p (line_table, next_stmt_loc)) return false; /* 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 (); */ 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 */ if (body_type == CPP_OPEN_BRACE) return false; /* Don't warn here about spurious semicolons. */ if (next_tok_type == CPP_SEMICOLON) return false; 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); /* 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_loc, &guard_vis_column, &guard_line_first_nws)) 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_loc, &next_stmt_vis_column, &next_stmt_line_first_nws)) return false; if (!get_visual_column (body_exploc, body_loc, &body_vis_column, &body_line_first_nws)) return false; if (!get_visual_column (guard_exploc, guard_loc, &guard_vis_column, &guard_line_first_nws)) 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)) 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. */ static const char * guard_tinfo_to_string (const token_indent_info &guard_tinfo) { switch (guard_tinfo.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"; 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)) { if (warning_at (guard_tinfo.location, OPT_Wmisleading_indentation, "this %qs clause does not guard...", guard_tinfo_to_string (guard_tinfo))) 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)); } }