Add support for three more string_view functions

[jeffbailey]

Summary

Add support for three more string_view functions

1. starts_with(char)
2. ends_with(char)
3. find_first_of(char, size_t)

Reimplemented trim in terms of the new starts_with and ends_with.

Tested:
New unit tests.

[gchatelet]

libc/src/__support/CPP/StringView.h

127–130

once we have starts_with and ends_with this can be rewritten as:

while (Copy.starts_with(C))
  Copy = Copy.drop_front();
while (Copy.ends_with(C))
  Copy = Copy.drop_back();

140–143

Let's express this as !empty() && front() == Prefix

155

Do you want to add the ends_with function for symmetry?

[jeffbailey]

Add new ends_with, unit tests, reimplement trim.

[jeffbailey]

PTAL

[sivachandra]

Suggestion for next time: When the patch touches only the libc directory, we should prefix the subject line with [libc] . Sorry for not noticing it on this patch.

[jeffbailey]

In D129618#3652465, @sivachandra wrote:

Suggestion for next time: When the patch touches only the libc directory, we should prefix the subject line with [libc] . Sorry for not noticing it on this patch.

Will do. Is there any way to add that in a presubmit? That seems like something that might be difficult to remember as we scale.

libc/src/__support/CPP/StringView.h

public:
   // The behavior is undefined if n > size().
   StringView remove_suffix(size_t N) const {
     if (N >= Len)
       return StringView();
     return StringView(Data, Len - N);
   }
 
   // An equivalent method is not available in std::string_view.
-  StringView trim(char C) const {
+  StringView trim(const char C) const {
     StringView Copy = *this;
-    while (!Copy.empty() && Copy.front() == C)
+    while (Copy.starts_with(C))
       Copy = Copy.drop_front();
-    while (!Copy.empty() && Copy.back() == C)
+    while (Copy.ends_with(C))
       Copy = Copy.drop_back();
     return Copy;
   }
 
   // Check if this string starts with the given Prefix.
   bool starts_with(StringView Prefix) const {
     return Len >= Prefix.Len &&
            compareMemory(Data, Prefix.Data, Prefix.Len) == 0;
   }
 
+  // Check if this string starts with the given Prefix.
+  bool starts_with(const char Prefix) const {
+    return !empty() && front() == Prefix;
+  }
+
+  // Check if this string ends with the given Prefix.
+  bool ends_with(const char Suffix) const {
+    return !empty() && back() == Suffix;
+  }
+
   // Check if this string ends with the given Suffix.
   bool ends_with(StringView Suffix) const {
     return Len >= Suffix.Len &&
            compareMemory(end() - Suffix.Len, Suffix.Data, Suffix.Len) == 0;
   }
 
   // Return a reference to the substring from [Start, Start + N).
   //
   // Start The index of the starting character in the substring; if the index is
   // npos or greater than the length of the string then the empty substring will
   // be returned.
   //
   // N The number of characters to included in the substring. If N exceeds the
   // number of characters remaining in the string, the string suffix (starting
   // with Start) will be returned.
   StringView substr(size_t Start, size_t N = npos) const {
     Start = min(Start, Len);
     return StringView(Data + Start, min(N, Len - Start));
   }
 
+  // Search for the first character matching the character
+  //
+  // Returns The index of the first character satisfying the character starting
+  // from From, or npos if not found.
+  size_t find_first_of(const char c, size_t From = 0) const noexcept {
+    StringView S = drop_front(From);
+    while (!S.empty()) {
+      if (S.front() == c)
+        return size() - S.size();
+      S = S.drop_front();
+    }
+    return npos;
+  }
+
   // Search for the first character satisfying the predicate Function
   //
   // Returns The index of the first character satisfying Function starting from
   // From, or npos if not found.
   template <typename F> size_t find_if(F Function, size_t From = 0) const {
     StringView S = drop_front(From);
     while (!S.empty()) {
       if (Function(S.front()))

libc/test/src/__support/CPP/stringview_test.cpp

TEST(LlvmLibcStringViewTest, Equals) {
   ASSERT_FALSE(v.equals(StringView("123")));
   ASSERT_FALSE(v.equals(StringView("abd")));
   ASSERT_FALSE(v.equals(StringView("aaa")));
   ASSERT_FALSE(v.equals(StringView("abcde")));
 }
 
 TEST(LlvmLibcStringViewTest, startsWith) {
   StringView v("abc");
+  ASSERT_TRUE(v.starts_with('a'));
   ASSERT_TRUE(v.starts_with(StringView("a")));
   ASSERT_TRUE(v.starts_with(StringView("ab")));
   ASSERT_TRUE(v.starts_with(StringView("abc")));
   ASSERT_TRUE(v.starts_with(StringView()));
   ASSERT_TRUE(v.starts_with(StringView("")));
+  ASSERT_FALSE(v.starts_with('1'));
   ASSERT_FALSE(v.starts_with(StringView("123")));
   ASSERT_FALSE(v.starts_with(StringView("abd")));
   ASSERT_FALSE(v.starts_with(StringView("aaa")));
   ASSERT_FALSE(v.starts_with(StringView("abcde")));
 }
 
+TEST(LlvmLibcStringViewTest, endsWith) {
+  StringView v("abc");
+  ASSERT_TRUE(v.ends_with('c'));
+  ASSERT_TRUE(v.ends_with(StringView("c")));
+  ASSERT_TRUE(v.ends_with(StringView("bc")));
+  ASSERT_TRUE(v.ends_with(StringView("abc")));
+  ASSERT_TRUE(v.ends_with(StringView()));
+  ASSERT_TRUE(v.ends_with(StringView("")));
+  ASSERT_FALSE(v.ends_with('1'));
+  ASSERT_FALSE(v.ends_with(StringView("123")));
+  ASSERT_FALSE(v.ends_with(StringView("abd")));
+  ASSERT_FALSE(v.ends_with(StringView("aaa")));
+  ASSERT_FALSE(v.ends_with(StringView("abcde")));
+}
+
 TEST(LlvmLibcStringViewTest, RemovePrefix) {
   StringView v("123456789");
 
   auto p = v.remove_prefix(0);
   ASSERT_EQ(p.size(), size_t(9));
   ASSERT_TRUE(p.equals(StringView("123456789")));
 
   p = v.remove_prefix(4);

 }
 
 TEST(LlvmLibcStringViewTest, ConsumeBack) {
   StringView Tmp("abc");
   ASSERT_FALSE(Tmp.consume_back("###"));
   ASSERT_TRUE(Tmp.consume_back("bc"));
   ASSERT_TRUE(Tmp.equals("a"));
 }
+
+TEST(LlvmLibcStringViewTest, FindFirstOf) {
+  StringView Tmp("abca");
+  ASSERT_TRUE(Tmp.find_first_of('a') == 0);
+  ASSERT_TRUE(Tmp.find_first_of('d') == StringView::npos);
+  ASSERT_TRUE(Tmp.find_first_of('b') == 1);
+  ASSERT_TRUE(Tmp.find_first_of('a', 0) == 0);
+  ASSERT_TRUE(Tmp.find_first_of('b', 1) == 1);
+  ASSERT_TRUE(Tmp.find_first_of('a', 1) == 3);
+  ASSERT_TRUE(Tmp.find_first_of('a', 42) == StringView::npos);
+  ASSERT_FALSE(Tmp.find_first_of('c') == 1);
+  ASSERT_FALSE(Tmp.find_first_of('c', 0) == 1);
+  ASSERT_FALSE(Tmp.find_first_of('c', 1) == 1);
+}