Remove copy paste (though I'm not sure it's much better), start work on {{ parse failure

Ast/include/Luau/Lexer.h

@@ -218,6 +218,7 @@ private:
     Lexeme readQuotedString();
 
     Lexeme readInterpolatedStringBegin();
+    std::optional<Lexeme> readInterpolatedStringSection(Position start, Lexeme::Type formatType);
 
     void readBackslashInString();
 

Ast/src/Lexer.cpp

@@ -602,35 +602,15 @@ Lexeme Lexer::readQuotedString()
 
 const Lexeme Lexer::nextInterpolatedString()
 {
-    // INTERP TODO: This is a copy-paste
     Position start = position();
-
     unsigned int startOffset = offset;
 
-    while (peekch() != '`')
+    std::optional<Lexeme> readSectionOpt = readInterpolatedStringSection(start, Lexeme::InterpStringMid);
+
+    if (auto readSection = readSectionOpt)
     {
-        switch (peekch())
-        {
-        case 0:
-        case '\r':
-        case '\n':
-            lexeme = Lexeme(Location(start, position()), Lexeme::BrokenString);
-            return lexeme;
-
-        case '\\':
-            readBackslashInString();
-            break;
-
-        case '{':
-            incrementInterpolatedStringDepth();
-
-            lexeme = Lexeme(Location(start, position()), Lexeme::InterpStringMid, &buffer[startOffset], offset - startOffset);
-            consume();
-            return lexeme;
-
-        default:
-            consume();
-        }
+        lexeme = *readSection;
+        return lexeme;
     }
 
     consume();
@@ -642,9 +622,20 @@ const Lexeme Lexer::nextInterpolatedString()
 Lexeme Lexer::readInterpolatedStringBegin()
 {
     Position start = position();
-
     consume();
 
+    std::optional<Lexeme> readSectionOpt = readInterpolatedStringSection(start, Lexeme::InterpStringBegin);
+
+    if (!readSectionOpt)
+    {
+        LUAU_ASSERT(!"INTERP TODO: Error if there was no interpolated expression");
+    }
+
+    return *readSectionOpt;
+}
+
+std::optional<Lexeme> Lexer::readInterpolatedStringSection(Position start, Lexeme::Type formatType)
+{
     unsigned int startOffset = offset;
 
     while (peekch() != '`')
@@ -654,27 +645,26 @@ Lexeme Lexer::readInterpolatedStringBegin()
         case 0:
         case '\r':
         case '\n':
-            return Lexeme(Location(start, position()), Lexeme::BrokenString);
+            return std::optional(Lexeme(Location(start, position()), Lexeme::BrokenString));
 
         case '\\':
             readBackslashInString();
             break;
 
         case '{':
+        {
             incrementInterpolatedStringDepth();
-            lexeme = Lexeme(Location(start, position()), Lexeme::InterpStringBegin, &buffer[startOffset], offset - startOffset);
+            auto lexemeOutput = Lexeme(Location(start, position()), Lexeme::InterpStringBegin, &buffer[startOffset], offset - startOffset);
             consume();
-            return lexeme;
+            return std::optional(lexemeOutput);
+        }
 
         default:
             consume();
         }
     }
 
-    consume();
-
-    // INTERP TODO: Error if there was no interpolated expression
-    LUAU_ASSERT(!"INTERP TODO: interpolated string without ending");
+    return std::nullopt;
 }
 
 Lexeme Lexer::readNumber(const Position& start, unsigned int startOffset)

tests/Parser.test.cpp

@@ -1034,6 +1034,21 @@ TEST_CASE_FIXTURE(Fixture, "parse_compound_assignment_error_multiple")
     }
 }
 
+TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_double_brace")
+{
+    try
+    {
+        parse(R"(
+            _ = `{{oops}}`
+        )");
+        FAIL("Expected ParseErrors to be thrown");
+    }
+    catch (const ParseErrors& e)
+    {
+        CHECK_EQ("INTERP TODO: Message", e.getErrors().front().getMessage());
+    }
+}
+
 TEST_CASE_FIXTURE(Fixture, "parse_nesting_based_end_detection")
 {
     try

tests/conformance/stringinterp.lua

@@ -18,9 +18,6 @@ assertEq(`The lock combinations are: {table.concat(combo, ", ")}`, "The lock com
 
 assertEq(`true = {true}`, "true = true")
 
--- -- INTERP TODO: Syntax error
--- -- assert(string.find(`{{ "nested braces!" }}`, "table"))
-
 local name = "Luau"
 assertEq(`Welcome to {
 	name