[llvm][mustache] Precommit test for Set Delimiter

Adds a new unit test for the Mustache Set Delimiter feature.

This test is written with inverted logic (`EXPECT_NE`) so that it
passes with the current implementation, which does not support
the feature. Once the feature is implemented, this test will fail,
signaling that the test logic should be flipped to `EXPECT_EQ`.

Author: ilovepi

llvm/unittests/Support/MustacheTest.cpp

@@ -1329,3 +1329,137 @@ TEST(MustacheTripleMustache, WithPadding) {
   EXPECT_EQ("|---|", Out);
 }
 
+TEST(MustacheDelimiters, PairBehavior) {
+  Value D = Object{{"text", "Hey!"}};
+  auto T = Template("{{=<% %>=}}(<%text%>)");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("(Hey!)", Out);
+}
+
+TEST(MustacheDelimiters, SpecialCharacters) {
+  Value D = Object{{"text", "It worked!"}};
+  auto T = Template("({{=[ ]=}}[text])");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("(It worked!)", Out);
+}
+
+TEST(MustacheDelimiters, Sections) {
+  Value D = Object{{"section", true}, {"data", "I got interpolated."}};
+  auto T = Template("[\n{{#section}}\n  {{data}}\n  |data|\n{{/section}}\n\n{{= "
+                    "| | =}}\n|#section|\n  {{data}}\n  |data|\n|/section|\n]\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[\n  I got interpolated.\n  |data|\n\n  {{data}}\n  I got "
+            "interpolated.\n]\n",
+            Out);
+}
+
+TEST(MustacheDelimiters, InvertedSections) {
+  Value D = Object{{"section", false}, {"data", "I got interpolated."}};
+  auto T = Template("[\n{{^section}}\n  {{data}}\n  |data|\n{{/section}}\n\n{{= "
+                    "| | =}}\n|^section|\n  {{data}}\n  |data|\n|/section|\n]\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[\n  I got interpolated.\n  |data|\n\n  {{data}}\n  I got "
+            "interpolated.\n]\n",
+            Out);
+}
+
+TEST(MustacheDelimiters, PartialInheritence) {
+  Value D = Object{{"value", "yes"}};
+  auto T = Template("[ {{>include}} ]\n{{= | | =}}\n[ |>include| ]\n");
+  T.registerPartial("include", ".{{value}}.");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[ .yes. ]\n[ .yes. ]\n", Out);
+}
+
+TEST(MustacheDelimiters, PostPartialBehavior) {
+  Value D = Object{{"value", "yes"}};
+  auto T = Template("[ {{>include}} ]\n[ .{{value}}.  .|value|. ]\n");
+  T.registerPartial("include", ".{{value}}. {{= | | =}} .|value|.");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[ .yes.  .yes. ]\n[ .yes.  .|value|. ]\n", Out);
+}
+
+TEST(MustacheDelimiters, SurroundingWhitespace) {
+  Value D = Object{};
+  auto T = Template("| {{=@ @=}} |");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ("|  |", Out);
+}
+
+TEST(MustacheDelimiters, OutlyingWhitespaceInline) {
+  Value D = Object{};
+  auto T = Template(" | {{=@ @=}}\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ(" | \n", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneTag) {
+  Value D = Object{};
+  auto T = Template("Begin.\n{{=@ @=}}\nEnd.\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("Begin.\nEnd.\n", Out);
+}
+
+TEST(MustacheDelimiters, IndentedStandaloneTag) {
+  Value D = Object{};
+  auto T = Template("Begin.\n  {{=@ @=}}\nEnd.\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("Begin.\nEnd.\n", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneLineEndings) {
+  Value D = Object{};
+  auto T = Template("|\r\n{{= @ @ =}}\r\n|");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("|\r\n|", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneWithoutPreviousLine) {
+  Value D = Object{};
+  auto T = Template("  {{=@ @=}}\n=");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("=", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneWithoutNewline) {
+  Value D = Object{};
+  auto T = Template("=\n  {{=@ @=}}");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("=\n", Out);
+}
+
+TEST(MustacheDelimiters, PairwithPadding) {
+  Value D = Object{};
+  auto T = Template("|{{= @   @ =}}|");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ("||", Out);
+}
+