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[core] Let StringRef carry a null pointer at zero length

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The generated api messages start their encode only string fields that way. starts_with,
compare and str() no longer hand a null pointer to memcmp or the std::string range
constructor when there is nothing to compare or copy, the class comment states the
contract, and gtest cases pin every member on a null, empty view.
This commit is contained in:
J. Nick Koston
2026-09-08 03:14:44 +02:00
parent 4c72948575
commit 63b5331e47
2 changed files with 43 additions and 3 deletions
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tests/components/core/test_string_ref.cpp
+35
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@@ -59,4 +59,39 @@ TEST(StringRefStartsWith, RefOverloadComparesOnlyTheViewedLength) {
EXPECT_TRUE(ref.starts_with(prefix));
}
// The generated api messages start their encode only string fields as a null pointer with zero
// length; every member must treat that exactly like the default constructed empty string.
TEST(StringRefNullEmpty, BehavesAsEmptyString) {
const StringRef null_empty{nullptr, 0};
const StringRef empty;
EXPECT_TRUE(null_empty.empty());
EXPECT_EQ(null_empty.size(), 0u);
EXPECT_EQ(null_empty.c_str(), nullptr);
EXPECT_TRUE(null_empty == empty);
EXPECT_TRUE(null_empty == "");
EXPECT_TRUE(null_empty == std::string());
EXPECT_EQ(null_empty.compare(empty), 0);
EXPECT_EQ(null_empty.compare(""), 0);
EXPECT_LT(null_empty.compare("a"), 0);
EXPECT_TRUE(null_empty.starts_with(""));
EXPECT_FALSE(null_empty.starts_with("a"));
EXPECT_EQ(null_empty.str(), std::string());
EXPECT_EQ(null_empty.substr(0), std::string());
EXPECT_EQ(null_empty.find('a'), std::string::npos);
EXPECT_EQ(null_empty.find("a"), std::string::npos);
char buf[4] = "xyz";
EXPECT_EQ(null_empty.copy(buf, sizeof(buf)), 0u);
EXPECT_EQ(null_empty.begin(), null_empty.end());
}
TEST(StringRefNullEmpty, ComparesAgainstText) {
const StringRef null_empty{nullptr, 0};
const StringRef text("abc", 3);
EXPECT_FALSE(null_empty == text);
EXPECT_FALSE(text == null_empty);
EXPECT_LT(null_empty.compare(text), 0);
EXPECT_GT(text.compare(null_empty), 0);
EXPECT_TRUE(text.starts_with(null_empty));
}
} // namespace esphome::core::testing