[llvm] r284364 - ADT: Use LLVM_NODISCARD instead of LLVM_ATTRIBUTE_UNUSED_RESULT for StringRef
Mehdi Amini via llvm-commits
llvm-commits at lists.llvm.org
Mon Nov 28 09:52:16 PST 2016
> On Nov 28, 2016, at 9:18 AM, David Blaikie via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>
> I'm going to +1 Zach here, this doesn't seem like a good use of the attribute.
>
> It's perfectly reasonable to have an API that returns an optionally useful StringRef (& I'd be fairly sure we have a few in the LLVM project already, but even if we don't I'd still be in favor of continuing to allow such API design without workarounds like void casts or extra attributes to opt out - especially considering templates in APIs that might expose such things indirectly (& possibly be unannotatable because they're in the STL))
Since the attribute was committed for some time and no failure was reported, that seems quite hypothetical.
I rather see a real use-case in our codebase before ditching something like that speculatively.
—
Mehdi
>
> LLVM_ATTRIBUTE_UNUSED_RESULT on a type was really designed/intended for types like llvm::Error (eg: http://google.github.io/google-api-cpp-client/latest/doxygen/classgoogleapis_1_1util_1_1Status.html <http://google.github.io/google-api-cpp-client/latest/doxygen/classgoogleapis_1_1util_1_1Status.html> ). It doesn't seem appropriate to put this on generic value types (& as Zach said - if that were the case we'd probably end up putting it on basically every type, and at that point should consider a generic warning for ignored return values - but I don't think that would be practical)
>
> - Dave
>
> On Sun, Oct 16, 2016 at 11:44 PM Justin Bogner via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: bogner
> Date: Mon Oct 17 01:35:23 2016
> New Revision: 284364
>
> URL: http://llvm.org/viewvc/llvm-project?rev=284364&view=rev <http://llvm.org/viewvc/llvm-project?rev=284364&view=rev>
> Log:
> ADT: Use LLVM_NODISCARD instead of LLVM_ATTRIBUTE_UNUSED_RESULT for StringRef
>
> Instead of annotating (most of) the StringRef API, we can just
> annotate the type directly. This is less code and it will warn in more
> cases.
>
> Modified:
> llvm/trunk/include/llvm/ADT/StringRef.h
>
> Modified: llvm/trunk/include/llvm/ADT/StringRef.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringRef.h?rev=284364&r1=284363&r2=284364&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringRef.h?rev=284364&r1=284363&r2=284364&view=diff>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/StringRef.h (original)
> +++ llvm/trunk/include/llvm/ADT/StringRef.h Mon Oct 17 01:35:23 2016
> @@ -44,7 +44,7 @@ namespace llvm {
> /// situations where the character data resides in some other buffer, whose
> /// lifetime extends past that of the StringRef. For this reason, it is not in
> /// general safe to store a StringRef.
> - class StringRef {
> + class LLVM_NODISCARD StringRef {
> public:
> typedef const char *iterator;
> typedef const char *const_iterator;
> @@ -281,8 +281,8 @@ namespace llvm {
> ///
> /// \returns The index of the first character satisfying \p F starting from
> /// \p From, or npos if not found.
> + LLVM_NODISCARD
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> size_t find_if(function_ref<bool(char)> F, size_t From = 0) const {
> StringRef S = drop_front(From);
> while (!S.empty()) {
> @@ -297,8 +297,8 @@ namespace llvm {
> ///
> /// \returns The index of the first character not satisfying \p F starting
> /// from \p From, or npos if not found.
> + LLVM_NODISCARD
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> size_t find_if_not(function_ref<bool(char)> F, size_t From = 0) const {
> return find_if([F](char c) { return !F(c); }, From);
> }
> @@ -500,7 +500,6 @@ namespace llvm {
> /// exceeds the number of characters remaining in the string, the string
> /// suffix (starting with \p Start) will be returned.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef substr(size_t Start, size_t N = npos) const {
> Start = std::min(Start, Length);
> return StringRef(Data + Start, std::min(N, Length - Start));
> @@ -510,7 +509,6 @@ namespace llvm {
> /// elements remaining. If \p N is greater than the length of the
> /// string, the entire string is returned.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef take_front(size_t N = 1) const {
> if (N >= size())
> return *this;
> @@ -521,7 +519,6 @@ namespace llvm {
> /// elements remaining. If \p N is greater than the length of the
> /// string, the entire string is returned.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef take_back(size_t N = 1) const {
> if (N >= size())
> return *this;
> @@ -531,7 +528,6 @@ namespace llvm {
> /// Return the longest prefix of 'this' such that every character
> /// in the prefix satisfies the given predicate.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef take_while(function_ref<bool(char)> F) const {
> return substr(0, find_if_not(F));
> }
> @@ -539,7 +535,6 @@ namespace llvm {
> /// Return the longest prefix of 'this' such that no character in
> /// the prefix satisfies the given predicate.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef take_until(function_ref<bool(char)> F) const {
> return substr(0, find_if(F));
> }
> @@ -547,7 +542,6 @@ namespace llvm {
> /// Return a StringRef equal to 'this' but with the first \p N elements
> /// dropped.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef drop_front(size_t N = 1) const {
> assert(size() >= N && "Dropping more elements than exist");
> return substr(N);
> @@ -556,7 +550,6 @@ namespace llvm {
> /// Return a StringRef equal to 'this' but with the last \p N elements
> /// dropped.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef drop_back(size_t N = 1) const {
> assert(size() >= N && "Dropping more elements than exist");
> return substr(0, size()-N);
> @@ -565,7 +558,6 @@ namespace llvm {
> /// Return a StringRef equal to 'this', but with all characters satisfying
> /// the given predicate dropped from the beginning of the string.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef drop_while(function_ref<bool(char)> F) const {
> return substr(find_if_not(F));
> }
> @@ -573,15 +565,14 @@ namespace llvm {
> /// Return a StringRef equal to 'this', but with all characters not
> /// satisfying the given predicate dropped from the beginning of the string.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef drop_until(function_ref<bool(char)> F) const {
> return substr(find_if(F));
> }
>
> /// Returns true if this StringRef has the given prefix and removes that
> /// prefix.
> + LLVM_NODISCARD
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> bool consume_front(StringRef Prefix) {
> if (!startswith(Prefix))
> return false;
> @@ -592,8 +583,8 @@ namespace llvm {
>
> /// Returns true if this StringRef has the given suffix and removes that
> /// suffix.
> + LLVM_NODISCARD
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> bool consume_back(StringRef Suffix) {
> if (!endswith(Suffix))
> return false;
> @@ -614,7 +605,6 @@ namespace llvm {
> /// will be returned. If this is less than \p Start, an empty string will
> /// be returned.
> LLVM_ATTRIBUTE_ALWAYS_INLINE
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef slice(size_t Start, size_t End) const {
> Start = std::min(Start, Length);
> End = std::min(std::max(Start, End), Length);
> @@ -709,42 +699,36 @@ namespace llvm {
>
> /// Return string with consecutive \p Char characters starting from the
> /// the left removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef ltrim(char Char) const {
> return drop_front(std::min(Length, find_first_not_of(Char)));
> }
>
> /// Return string with consecutive characters in \p Chars starting from
> /// the left removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef ltrim(StringRef Chars = " \t\n\v\f\r") const {
> return drop_front(std::min(Length, find_first_not_of(Chars)));
> }
>
> /// Return string with consecutive \p Char characters starting from the
> /// right removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef rtrim(char Char) const {
> return drop_back(Length - std::min(Length, find_last_not_of(Char) + 1));
> }
>
> /// Return string with consecutive characters in \p Chars starting from
> /// the right removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef rtrim(StringRef Chars = " \t\n\v\f\r") const {
> return drop_back(Length - std::min(Length, find_last_not_of(Chars) + 1));
> }
>
> /// Return string with consecutive \p Char characters starting from the
> /// left and right removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef trim(char Char) const {
> return ltrim(Char).rtrim(Char);
> }
>
> /// Return string with consecutive characters in \p Chars starting from
> /// the left and right removed.
> - LLVM_ATTRIBUTE_UNUSED_RESULT
> StringRef trim(StringRef Chars = " \t\n\v\f\r") const {
> return ltrim(Chars).rtrim(Chars);
> }
>
>
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