Should this be in -Wextra-semi? It seems weird to have to pass both -Wextra-semi and -Wextra-semi-stmt.
(Also, we generally try to not add DefaultIgnore warnings. I think this is a useful warning though, and other than others in this thread I think it'd be good to have -Wextra-semi in -Wall. But I don't feel strongly about that part.) On Tue, Nov 20, 2018 at 2:01 PM Roman Lebedev via cfe-commits < cfe-commits@lists.llvm.org> wrote: > Author: lebedevri > Date: Tue Nov 20 10:59:05 2018 > New Revision: 347339 > > URL: http://llvm.org/viewvc/llvm-project?rev=347339&view=rev > Log: > [clang][Parse] Diagnose useless null statements / empty init-statements > > Summary: > clang has `-Wextra-semi` (D43162), which is not dictated by the currently > selected standard. > While that is great, there is at least one more source of need-less semis > - 'null statements'. > Sometimes, they are needed: > ``` > for(int x = 0; continueToDoWork(x); x++) > ; // Ugly code, but the semi is needed here. > ``` > > But sometimes they are just there for no reason: > ``` > switch(X) { > case 0: > return -2345; > case 5: > return 0; > default: > return 42; > }; // <- oops > > ;;;;;;;;;;; <- OOOOPS, still not diagnosed. Clearly this is junk. > ``` > > Additionally: > ``` > if(; // <- empty init-statement > true) > ; > > switch (; // empty init-statement > x) { > ... > } > > for (; // <- empty init-statement > int y : S()) > ; > } > > As usual, things may or may not go sideways in the presence of macros. > While evaluating this diag on my codebase of interest, it was > unsurprisingly > discovered that Google Test macros are *very* prone to this. > And it seems many issues are deep within the GTest itself, not > in the snippets passed from the codebase that uses GTest. > > So after some thought, i decided not do issue a diagnostic if the semi > is within *any* macro, be it either from the normal header, or system > header. > > Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=39111 | PR39111 ]] > > Reviewers: rsmith, aaron.ballman, efriedma > > Reviewed By: aaron.ballman > > Subscribers: cfe-commits > > Differential Revision: https://reviews.llvm.org/D52695 > > Added: > > cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt-in-init-statement.cpp > cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt.cpp > Modified: > cfe/trunk/docs/ReleaseNotes.rst > cfe/trunk/include/clang/Basic/DiagnosticGroups.td > cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td > cfe/trunk/include/clang/Parse/Parser.h > cfe/trunk/lib/Parse/ParseExprCXX.cpp > cfe/trunk/lib/Parse/ParseStmt.cpp > > Modified: cfe/trunk/docs/ReleaseNotes.rst > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/ReleaseNotes.rst?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/docs/ReleaseNotes.rst (original) > +++ cfe/trunk/docs/ReleaseNotes.rst Tue Nov 20 10:59:05 2018 > @@ -55,6 +55,63 @@ Major New Features > Improvements to Clang's diagnostics > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > +- ``-Wextra-semi-stmt`` is a new diagnostic that diagnoses extra > semicolons, > + much like ``-Wextra-semi``. This new diagnostic diagnoses all > *unnecessary* > + null statements (expression statements without an expression), unless: > the > + semicolon directly follows a macro that was expanded to nothing or if > the > + semicolon is within the macro itself. This applies to macros defined in > system > + headers as well as user-defined macros. > + > + .. code-block:: c++ > + > + #define MACRO(x) int x; > + #define NULLMACRO(varname) > + > + void test() { > + ; // <- warning: ';' with no preceding expression is a null > statement > + > + while (true) > + ; // OK, it is needed. > + > + switch (my_enum) { > + case E1: > + // stuff > + break; > + case E2: > + ; // OK, it is needed. > + } > + > + MACRO(v0;) // Extra semicolon, but within macro, so ignored. > + > + MACRO(v1); // <- warning: ';' with no preceding expression is a > null statement > + > + NULLMACRO(v2); // ignored, NULLMACRO expanded to nothing. > + } > + > +- ``-Wempty-init-stmt`` is a new diagnostic that diagnoses empty > init-statements > + of ``if``, ``switch``, ``range-based for``, unless: the semicolon > directly > + follows a macro that was expanded to nothing or if the semicolon is > within the > + macro itself (both macros from system headers, and normal macros). This > + diagnostic is in the ``-Wextra-semi-stmt`` group and is enabled in > + ``-Wextra``. > + > + .. code-block:: c++ > + > + void test() { > + if(; // <- warning: init-statement of 'if' is a null statement > + true) > + ; > + > + switch (; // <- warning: init-statement of 'switch' is a null > statement > + x) { > + ... > + } > + > + for (; // <- warning: init-statement of 'range-based for' is a > null statement > + int y : S()) > + ; > + } > + > > Non-comprehensive list of changes in this release > ------------------------------------------------- > > Modified: cfe/trunk/include/clang/Basic/DiagnosticGroups.td > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/include/clang/Basic/DiagnosticGroups.td (original) > +++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td Tue Nov 20 10:59:05 > 2018 > @@ -162,6 +162,8 @@ def GNUEmptyStruct : DiagGroup<"gnu-empt > def ExtraTokens : DiagGroup<"extra-tokens">; > def CXX98CompatExtraSemi : DiagGroup<"c++98-compat-extra-semi">; > def CXX11ExtraSemi : DiagGroup<"c++11-extra-semi">; > +def EmptyInitStatement : DiagGroup<"empty-init-stmt">; > +def ExtraSemiStmt : DiagGroup<"extra-semi-stmt", [EmptyInitStatement]>; > def ExtraSemi : DiagGroup<"extra-semi", [CXX98CompatExtraSemi, > CXX11ExtraSemi]>; > > @@ -768,7 +770,8 @@ def Extra : DiagGroup<"extra", [ > MissingMethodReturnType, > SignCompare, > UnusedParameter, > - NullPointerArithmetic > + NullPointerArithmetic, > + EmptyInitStatement > ]>; > > def Most : DiagGroup<"most", [ > > Modified: cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td (original) > +++ cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td Tue Nov 20 > 10:59:05 2018 > @@ -53,6 +53,10 @@ def ext_extra_semi_cxx11 : Extension< > def warn_extra_semi_after_mem_fn_def : Warning< > "extra ';' after member function definition">, > InGroup<ExtraSemi>, DefaultIgnore; > +def warn_null_statement : Warning< > + "empty expression statement has no effect; " > + "remove unnecessary ';' to silence this warning">, > + InGroup<ExtraSemiStmt>, DefaultIgnore; > > def ext_thread_before : Extension<"'__thread' before '%0'">; > def ext_keyword_as_ident : ExtWarn< > @@ -554,6 +558,9 @@ def ext_for_range_init_stmt : ExtWarn< > def warn_cxx17_compat_for_range_init_stmt : Warning< > "range-based for loop initialization statements are incompatible with " > "C++ standards before C++2a">, DefaultIgnore, InGroup<CXXPre2aCompat>; > +def warn_empty_init_statement : Warning< > + "empty initialization statement of '%select{if|switch|range-based > for}0' " > + "has no effect">, InGroup<EmptyInitStatement>, DefaultIgnore; > > // C++ derived classes > def err_dup_virtual : Error<"duplicate 'virtual' in base specifier">; > > Modified: cfe/trunk/include/clang/Parse/Parser.h > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Parse/Parser.h?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/include/clang/Parse/Parser.h (original) > +++ cfe/trunk/include/clang/Parse/Parser.h Tue Nov 20 10:59:05 2018 > @@ -1888,6 +1888,7 @@ private: > StmtResult ParseCompoundStatement(bool isStmtExpr, > unsigned ScopeFlags); > void ParseCompoundStatementLeadingPragmas(); > + bool ConsumeNullStmt(StmtVector &Stmts); > StmtResult ParseCompoundStatementBody(bool isStmtExpr = false); > bool ParseParenExprOrCondition(StmtResult *InitStmt, > Sema::ConditionResult &CondResult, > > Modified: cfe/trunk/lib/Parse/ParseExprCXX.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseExprCXX.cpp?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/lib/Parse/ParseExprCXX.cpp (original) > +++ cfe/trunk/lib/Parse/ParseExprCXX.cpp Tue Nov 20 10:59:05 2018 > @@ -1773,7 +1773,13 @@ Sema::ConditionResult Parser::ParseCXXCo > // if (; true); > if (InitStmt && Tok.is(tok::semi)) { > WarnOnInit(); > - SourceLocation SemiLoc = ConsumeToken(); > + SourceLocation SemiLoc = Tok.getLocation(); > + if (!Tok.hasLeadingEmptyMacro() && !SemiLoc.isMacroID()) { > + Diag(SemiLoc, diag::warn_empty_init_statement) > + << (CK == Sema::ConditionKind::Switch) > + << FixItHint::CreateRemoval(SemiLoc); > + } > + ConsumeToken(); > *InitStmt = Actions.ActOnNullStmt(SemiLoc); > return ParseCXXCondition(nullptr, Loc, CK); > } > > Modified: cfe/trunk/lib/Parse/ParseStmt.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseStmt.cpp?rev=347339&r1=347338&r2=347339&view=diff > > ============================================================================== > --- cfe/trunk/lib/Parse/ParseStmt.cpp (original) > +++ cfe/trunk/lib/Parse/ParseStmt.cpp Tue Nov 20 10:59:05 2018 > @@ -930,6 +930,34 @@ void Parser::ParseCompoundStatementLeadi > > } > > +/// Consume any extra semi-colons resulting in null statements, > +/// returning true if any tok::semi were consumed. > +bool Parser::ConsumeNullStmt(StmtVector &Stmts) { > + if (!Tok.is(tok::semi)) > + return false; > + > + SourceLocation StartLoc = Tok.getLocation(); > + SourceLocation EndLoc; > + > + while (Tok.is(tok::semi) && !Tok.hasLeadingEmptyMacro() && > + Tok.getLocation().isValid() && !Tok.getLocation().isMacroID()) { > + EndLoc = Tok.getLocation(); > + > + // Don't just ConsumeToken() this tok::semi, do store it in AST. > + StmtResult R = ParseStatementOrDeclaration(Stmts, ACK_Any); > + if (R.isUsable()) > + Stmts.push_back(R.get()); > + } > + > + // Did not consume any extra semi. > + if (EndLoc.isInvalid()) > + return false; > + > + Diag(StartLoc, diag::warn_null_statement) > + << FixItHint::CreateRemoval(SourceRange(StartLoc, EndLoc)); > + return true; > +} > + > /// ParseCompoundStatementBody - Parse a sequence of statements and > invoke the > /// ActOnCompoundStmt action. This expects the '{' to be the current > token, and > /// consume the '}' at the end of the block. It does not manipulate the > scope > @@ -992,6 +1020,9 @@ StmtResult Parser::ParseCompoundStatemen > continue; > } > > + if (ConsumeNullStmt(Stmts)) > + continue; > + > StmtResult R; > if (Tok.isNot(tok::kw___extension__)) { > R = ParseStatementOrDeclaration(Stmts, ACK_Any); > @@ -1588,10 +1619,15 @@ StmtResult Parser::ParseForStatement(Sou > ParsedAttributesWithRange attrs(AttrFactory); > MaybeParseCXX11Attributes(attrs); > > + SourceLocation EmptyInitStmtSemiLoc; > + > // Parse the first part of the for specifier. > if (Tok.is(tok::semi)) { // for (; > ProhibitAttributes(attrs); > // no first part, eat the ';'. > + SourceLocation SemiLoc = Tok.getLocation(); > + if (!Tok.hasLeadingEmptyMacro() && !SemiLoc.isMacroID()) > + EmptyInitStmtSemiLoc = SemiLoc; > ConsumeToken(); > } else if (getLangOpts().CPlusPlus && Tok.is(tok::identifier) && > isForRangeIdentifier()) { > @@ -1723,6 +1759,11 @@ StmtResult Parser::ParseForStatement(Sou > : diag::ext_for_range_init_stmt) > << (FirstPart.get() ? FirstPart.get()->getSourceRange() > : SourceRange()); > + if (EmptyInitStmtSemiLoc.isValid()) { > + Diag(EmptyInitStmtSemiLoc, diag::warn_empty_init_statement) > + << /*for-loop*/ 2 > + << FixItHint::CreateRemoval(EmptyInitStmtSemiLoc); > + } > } > } else { > ExprResult SecondExpr = ParseExpression(); > > Added: > cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt-in-init-statement.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt-in-init-statement.cpp?rev=347339&view=auto > > ============================================================================== > --- > cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt-in-init-statement.cpp > (added) > +++ > cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt-in-init-statement.cpp > Tue Nov 20 10:59:05 2018 > @@ -0,0 +1,64 @@ > +// RUN: %clang_cc1 -fsyntax-only -Wextra -std=c++2a -verify %s > +// RUN: %clang_cc1 -fsyntax-only -Wextra-semi-stmt -std=c++2a -verify %s > +// RUN: %clang_cc1 -fsyntax-only -Wempty-init-stmt -std=c++2a -verify %s > +// RUN: cp %s %t > +// RUN: %clang_cc1 -x c++ -Wempty-init-stmt -std=c++2a -fixit %t > +// RUN: %clang_cc1 -x c++ -Wempty-init-stmt -std=c++2a -Werror %t > + > +struct S { > + int *begin(); > + int *end(); > +}; > + > +void naive(int x) { > + if (; true) // expected-warning {{empty initialization statement of > 'if' has no effect}} > + ; > + > + switch (; x) { // expected-warning {{empty initialization statement of > 'switch' has no effect}} > + } > + > + for (; int y : S()) // expected-warning {{empty initialization > statement of 'range-based for' has no effect}} > + ; > + > + for (;;) // OK > + ; > +} > + > +#define NULLMACRO > + > +void with_null_macro(int x) { > + if (NULLMACRO; true) > + ; > + > + switch (NULLMACRO; x) { > + } > + > + for (NULLMACRO; int y : S()) > + ; > +} > + > +#define SEMIMACRO ; > + > +void with_semi_macro(int x) { > + if (SEMIMACRO true) > + ; > + > + switch (SEMIMACRO x) { > + } > + > + for (SEMIMACRO int y : S()) > + ; > +} > + > +#define PASSTHROUGHMACRO(x) x > + > +void with_passthrough_macro(int x) { > + if (PASSTHROUGHMACRO(;) true) > + ; > + > + switch (PASSTHROUGHMACRO(;) x) { > + } > + > + for (PASSTHROUGHMACRO(;) int y : S()) > + ; > +} > > Added: cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt.cpp?rev=347339&view=auto > > ============================================================================== > --- cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt.cpp (added) > +++ cfe/trunk/test/Parser/extra-semi-resulting-in-nullstmt.cpp Tue Nov 20 > 10:59:05 2018 > @@ -0,0 +1,96 @@ > +// RUN: %clang_cc1 -fsyntax-only -Wextra-semi-stmt -verify %s > +// RUN: cp %s %t > +// RUN: %clang_cc1 -x c++ -Wextra-semi-stmt -fixit %t > +// RUN: %clang_cc1 -x c++ -Wextra-semi-stmt -Werror %t > + > +#define GOODMACRO(varname) int varname > +#define BETTERMACRO(varname) GOODMACRO(varname); > +#define NULLMACRO(varname) > + > +enum MyEnum { > + E1, > + E2 > +}; > + > +void test() { > + ; // expected-warning {{empty expression statement has no effect; > remove unnecessary ';' to silence this warning}} > + ; > + > + // This removal of extra semi also consumes all the comments. > + // clang-format: off > + ;;; > + // clang-format: on > + > + // clang-format: off > + ;NULLMACRO(ZZ); > + // clang-format: on > + > + {}; // expected-warning {{empty expression statement has no effect; > remove unnecessary ';' to silence this warning}} > + > + { > + ; // expected-warning {{empty expression statement has no effect; > remove unnecessary ';' to silence this warning}} > + } > + > + if (true) { > + ; // expected-warning {{empty expression statement has no effect; > remove unnecessary ';' to silence this warning}} > + } > + > + GOODMACRO(v0); // OK > + > + GOODMACRO(v1;) // OK > + > + BETTERMACRO(v2) // OK > + > + BETTERMACRO(v3;) // Extra ';', but within macro expansion, so ignored. > + > + BETTERMACRO(v4); // expected-warning {{empty expression statement has > no effect; remove unnecessary ';' to silence this warning}} > + > + BETTERMACRO(v5;); // expected-warning {{empty expression statement has > no effect; remove unnecessary ';' to silence this warning}} > + > + NULLMACRO(v6) // OK > + > + NULLMACRO(v7); // OK. This could be either GOODMACRO() or BETTERMACRO() > situation, so we can't know we can drop it. > + > + if (true) > + ; // OK > + > + while (true) > + ; // OK > + > + do > + ; // OK > + while (true); > + > + for (;;) // OK > + ; // OK > + > + MyEnum my_enum; > + switch (my_enum) { > + case E1: > + // stuff > + break; > + case E2:; // OK > + } > + > + for (;;) { > + for (;;) { > + goto contin_outer; > + } > + contin_outer:; // OK > + } > +} > + > +; > + > +namespace NS {}; > + > +void foo(int x) { > + switch (x) { > + case 0: > + [[fallthrough]]; > + case 1: > + return; > + } > +} > + > +[[]]; > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >
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