Basic string interpolation proof of concept

Ast/include/Luau/Ast.h

@@ -134,6 +134,10 @@ public:
     {
         return visit((class AstExpr*)node);
     }
+    virtual bool visit(class AstExprInterpString* node)
+    {
+        return visit((class AstExpr*)node);
+    }
     virtual bool visit(class AstExprError* node)
     {
         return visit((class AstExpr*)node);
@@ -722,6 +726,19 @@ public:
     AstExpr* falseExpr;
 };
 
+class AstExprInterpString : public AstExpr
+{
+public:
+    LUAU_RTTI(AstExprInterpString)
+
+    AstExprInterpString(const Location& location, const AstArray<AstArray<char>>& strings, const AstArray<AstExpr*>& expressions);
+
+    void visit(AstVisitor* visitor) override;
+
+    AstArray<AstArray<char>> strings;
+    AstArray<AstExpr*> expressions;
+};
+
 class AstStatBlock : public AstStat
 {
 public:

Ast/include/Luau/Lexer.h

@@ -61,6 +61,10 @@ struct Lexeme
         SkinnyArrow,
         DoubleColon,
 
+        InterpStringBegin,
+        InterpStringMid,
+        InterpStringEnd,
+
         AddAssign,
         SubAssign,
         MulAssign,
@@ -166,6 +170,11 @@ public:
 
     void setSkipComments(bool skip);
     void setReadNames(bool read);
+    void setReadAsInterpolatedStringExpression(bool read);
+
+    void incrementInterpolatedStringDepth();
+    void decrementInterpolatedStringDepth();
+    const Lexeme nextInterpolatedString();
 
     const Location& previousLocation() const
     {
@@ -208,6 +217,10 @@ private:
     Lexeme readLongString(const Position& start, int sep, Lexeme::Type ok, Lexeme::Type broken);
     Lexeme readQuotedString();
 
+    Lexeme readInterpolatedStringBegin();
+
+    void readBackslashInString();
+
     std::pair<AstName, Lexeme::Type> readName();
 
     Lexeme readNumber(const Position& start, unsigned int startOffset);
@@ -231,6 +244,9 @@ private:
 
     bool skipComments;
     bool readNames;
+    bool readAsInterpolatedStringExpression;
+
+    unsigned int interpolatedStringDepth;
 };
 
 inline bool isSpace(char ch)

Ast/include/Luau/Parser.h

@@ -228,6 +228,9 @@ private:
     // TODO: Add grammar rules here?
     AstExpr* parseIfElseExpr();
 
+    // INTERP TODO: Grammar
+    AstExpr* parseInterpString();
+
     // Name
     std::optional<Name> parseNameOpt(const char* context = nullptr);
     Name parseName(const char* context = nullptr);

Ast/src/Ast.cpp

@@ -348,6 +348,22 @@ AstExprError::AstExprError(const Location& location, const AstArray<AstExpr*>& e
 {
 }
 
+AstExprInterpString::AstExprInterpString(const Location& location, const AstArray<AstArray<char>>& strings, const AstArray<AstExpr*>& expressions)
+    : AstExpr(ClassIndex(), location)
+    , strings(strings)
+    , expressions(expressions)
+{
+}
+
+void AstExprInterpString::visit(AstVisitor* visitor)
+{
+    if (visitor->visit(this))
+    {
+        for (AstExpr* expr : expressions)
+            expr->visit(visitor);
+    }
+}
+
 void AstExprError::visit(AstVisitor* visitor)
 {
     if (visitor->visit(this))

Ast/src/Lexer.cpp

@@ -89,7 +89,16 @@ Lexeme::Lexeme(const Location& location, Type type, const char* data, size_t siz
     , length(unsigned(size))
     , data(data)
 {
-    LUAU_ASSERT(type == RawString || type == QuotedString || type == Number || type == Comment || type == BlockComment);
+    LUAU_ASSERT( \
+        type == RawString \
+        || type == QuotedString \
+        || type == InterpStringBegin \
+        || type == InterpStringMid \
+        || type == InterpStringEnd \
+        || type == Number \
+        || type == Comment \
+        || type == BlockComment \
+    );
 }
 
 Lexeme::Lexeme(const Location& location, Type type, const char* name)
@@ -332,6 +341,8 @@ Lexer::Lexer(const char* buffer, size_t bufferSize, AstNameTable& names)
     , names(names)
     , skipComments(false)
     , readNames(true)
+    , readAsInterpolatedStringExpression(true)
+    , interpolatedStringDepth(0)
 {
 }
 
@@ -345,6 +356,22 @@ void Lexer::setReadNames(bool read)
     readNames = read;
 }
 
+// INTERP TODO: Probably not necessary
+void Lexer::setReadAsInterpolatedStringExpression(bool read)
+{
+    readAsInterpolatedStringExpression = read;
+}
+
+void Lexer::incrementInterpolatedStringDepth()
+{
+    interpolatedStringDepth++;
+}
+
+void Lexer::decrementInterpolatedStringDepth()
+{
+    interpolatedStringDepth--;
+}
+
 const Lexeme& Lexer::next()
 {
     return next(this->skipComments, true);
@@ -515,6 +542,31 @@ Lexeme Lexer::readLongString(const Position& start, int sep, Lexeme::Type ok, Le
     return Lexeme(Location(start, position()), broken);
 }
 
+void Lexer::readBackslashInString()
+{
+    consume();
+    switch (peekch())
+    {
+    case '\r':
+        consume();
+        if (peekch() == '\n')
+            consume();
+        break;
+
+    case 0:
+        break;
+
+    case 'z':
+        consume();
+        while (isSpace(peekch()))
+            consume();
+        break;
+
+    default:
+        consume();
+    }
+}
+
 Lexeme Lexer::readQuotedString()
 {
     Position start = position();
@@ -535,27 +587,7 @@ Lexeme Lexer::readQuotedString()
             return Lexeme(Location(start, position()), Lexeme::BrokenString);
 
         case '\\':
-            consume();
-            switch (peekch())
-            {
-            case '\r':
-                consume();
-                if (peekch() == '\n')
-                    consume();
-                break;
-
-            case 0:
-                break;
-
-            case 'z':
-                consume();
-                while (isSpace(peekch()))
-                    consume();
-                break;
-
-            default:
-                consume();
-            }
+            readBackslashInString();
             break;
 
         default:
@@ -568,6 +600,82 @@ Lexeme Lexer::readQuotedString()
     return Lexeme(Location(start, position()), Lexeme::QuotedString, &buffer[startOffset], offset - startOffset - 1);
 }
 
+const Lexeme Lexer::nextInterpolatedString()
+{
+    // INTERP TODO: This is a copy-paste
+    Position start = position();
+
+    unsigned int startOffset = offset;
+
+    while (peekch() != '`')
+    {
+        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);
+            return lexeme;
+
+        default:
+            consume();
+        }
+    }
+
+    consume();
+
+    lexeme = Lexeme(Location(start, position()), Lexeme::InterpStringEnd, &buffer[startOffset], offset - startOffset - 1);
+    return lexeme;
+}
+
+Lexeme Lexer::readInterpolatedStringBegin()
+{
+    Position start = position();
+
+    consume();
+
+    unsigned int startOffset = offset;
+
+    while (peekch() != '`')
+    {
+        switch (peekch())
+        {
+        case 0:
+        case '\r':
+        case '\n':
+            return Lexeme(Location(start, position()), Lexeme::BrokenString);
+
+        case '\\':
+            readBackslashInString();
+            break;
+
+        case '{':
+            incrementInterpolatedStringDepth();
+            lexeme = Lexeme(Location(start, position()), Lexeme::InterpStringBegin, &buffer[startOffset], offset - startOffset);
+            consume();
+            return lexeme;
+
+        default:
+            consume();
+        }
+    }
+
+    consume();
+
+    // INTERP TODO: Error if there was no interpolated expression
+    LUAU_ASSERT(!"INTERP TODO: interpolated string without ending");
+}
+
 Lexeme Lexer::readNumber(const Position& start, unsigned int startOffset)
 {
     LUAU_ASSERT(isDigit(peekch()));
@@ -716,6 +824,9 @@ Lexeme Lexer::readNext()
     case '\'':
         return readQuotedString();
 
+    case '`':
+        return readInterpolatedStringBegin();
+
     case '.':
         consume();
 

Ast/src/Parser.cpp

@@ -2197,6 +2197,10 @@ AstExpr* Parser::parseSimpleExpr()
     {
         return parseString();
     }
+    else if (lexer.current().type == Lexeme::InterpStringBegin)
+    {
+        return parseInterpString();
+    }
     else if (lexer.current().type == Lexeme::BrokenString)
     {
         nextLexeme();
@@ -2615,6 +2619,70 @@ AstExpr* Parser::parseString()
         return reportExprError(location, {}, "String literal contains malformed escape sequence");
 }
 
+AstExpr* Parser::parseInterpString()
+{
+    std::vector<AstArray<char>> strings;
+    std::vector<AstExpr*> expressions;
+
+    // INTERP TODO: Compile to ("text"):format(...)
+    do {
+        auto currentLexeme = lexer.current();
+        LUAU_ASSERT(currentLexeme.type == Lexeme::InterpStringBegin || currentLexeme.type == Lexeme::InterpStringMid || currentLexeme.type == Lexeme::InterpStringEnd);
+
+        Location location = currentLexeme.location;
+
+        // INTERP TODO: Maybe 1 off?
+        Location startOfBrace = Location(location.end, 1);
+
+        scratchData.assign(currentLexeme.data, currentLexeme.length);
+
+        if (!Lexer::fixupQuotedString(scratchData))
+        {
+            nextLexeme();
+            return reportExprError(location, {}, "Interpolated string literal contains malformed escape sequence");
+        }
+
+        AstArray<char> chars = copy(scratchData);
+
+        nextLexeme();
+
+        strings.push_back(chars);
+
+        if (currentLexeme.type == Lexeme::InterpStringEnd)
+        {
+            // INTERP CODE REVIEW: I figure this isn't the right way to do this.
+            // From what I could gather, I'm expected to have strings and expressions be TempVector from the beginning.
+            // Everything that does that uses a scratch value.
+            // But I would think I would also be expected to use an existing scratch, like `scratchExpr`, in which case
+            // my assumption is that a nested expression would clash the scratches?
+            AstArray<AstArray<char>> stringsArray = copy(strings.data(), strings.size());
+            AstArray<AstExpr*> expressionsArray = copy(expressions.data(), expressions.size());
+
+            return allocator.alloc<AstExprInterpString>(location, stringsArray, expressionsArray);
+        }
+
+        AstExpr* expression = parseExpr();
+
+        // expectMatchAndConsume('}', Lexeme(startOfBrace, '{'));
+
+        // INTERP CODE REVIEW: I want to use expectMatchAndConsume, but using that
+        // consumes the rest of the string, not the `}`
+        if (lexer.current().type != static_cast<Lexeme::Type>(static_cast<unsigned char>('}'))) {
+            return reportExprError(location, {}, "Expected '}' after interpolated string expression");
+        }
+
+        expressions.push_back(expression);
+
+        lexer.decrementInterpolatedStringDepth();
+
+        auto next = lexer.nextInterpolatedString();
+        if (next.type == Lexeme::BrokenString)
+        {
+            return reportExprError(location, {}, "Malformed interpolated string");
+        }
+    } while (true);
+}
+
 AstLocal* Parser::pushLocal(const Binding& binding)
 {
     const Name& name = binding.name;

Compiler/src/Compiler.cpp

@@ -1477,6 +1477,57 @@ struct Compiler
         }
     }
 
+    void compileExprInterpString(AstExprInterpString* expr, uint8_t target, bool targetTemp)
+    {
+        // INTERP TODO: percent sign escape
+        std::string formatString;
+
+        unsigned int stringsLeft = expr->strings.size;
+
+        for (AstArray<char> const& string : expr->strings)
+        {
+            formatString += string.data;
+
+            stringsLeft--;
+
+            // INTERP TODO: %*
+            if (stringsLeft > 0)
+                formatString += "%s";
+        }
+
+        std::string& formatStringRef = interpFormatStrings.emplace_back(formatString);
+
+        AstArray<char> formatStringArray{formatStringRef.data(), formatStringRef.size()};
+
+        int32_t formatStringIndex = bytecode.addConstantString(sref(formatStringArray));
+        if (formatStringIndex < 0)
+            CompileError::raise(expr->location, "Exceeded constant limit; simplify the code to compile");
+
+        bytecode.emitABC(LOP_LOADK, target, formatStringIndex, 0);
+
+        // INTERP CODE REVIEW: Why do I need this?
+        // If I don't, it emits `LOADK R1 K1` instead of `LOADK R2 K1`,
+        // and it gives the error "missing argument 2".
+        allocReg(expr, 1);
+
+        RegScope rs(this);
+
+        for (AstExpr* expression : expr->expressions)
+        {
+            compileExprAuto(expression, rs);
+        }
+
+        BytecodeBuilder::StringRef formatMethod = sref(AstName("format"));
+
+        int32_t formatMethodIndex = bytecode.addConstantString(formatMethod);
+        if (formatMethodIndex < 0)
+            CompileError::raise(expr->location, "Exceeded constant limit; simplify the code to compile");
+
+        bytecode.emitABC(LOP_NAMECALL, target, target, uint8_t(BytecodeBuilder::getStringHash(formatMethod)));
+        bytecode.emitAux(formatMethodIndex);
+        bytecode.emitABC(LOP_CALL, target, expr->expressions.size + 2, 2);
+    }
+
     static uint8_t encodeHashSize(unsigned int hashSize)
     {
         size_t hashSizeLog2 = 0;
@@ -1951,6 +2002,10 @@ struct Compiler
         {
             compileExprIfElse(expr, target, targetTemp);
         }
+        else if (AstExprInterpString* interpString = node->as<AstExprInterpString>())
+        {
+            compileExprInterpString(interpString, target, targetTemp);
+        }
         else
         {
             LUAU_ASSERT(!"Unknown expression type");
@@ -3575,6 +3630,7 @@ struct Compiler
     std::vector<Loop> loops;
     std::vector<InlineFrame> inlineFrames;
     std::vector<Capture> captures;
+    std::vector<std::string> interpFormatStrings;
 };
 
 void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, const AstNameTable& names, const CompileOptions& inputOptions)

Compiler/src/ConstantFolding.cpp

@@ -349,6 +349,11 @@ struct ConstantVisitor : AstVisitor
             if (cond.type != Constant::Type_Unknown)
                 result = cond.isTruthful() ? trueExpr : falseExpr;
         }
+        else if (AstExprInterpString* interpString = node->as<AstExprInterpString>())
+        {
+            // INTERP CODE REVIEW: This can theoretically fold something like `debug mode: {DEBUG_MODE}` where DEBUG_MODE is true.
+            // Is this necessary or just something we can do later?
+        }
         else
         {
             LUAU_ASSERT(!"Unknown expression type");

tests/Conformance.test.cpp

@@ -291,7 +291,13 @@ TEST_CASE("Clear")
 
 TEST_CASE("Strings")
 {
-    runConformance("strings.lua");
+    // INTERP TODO: strings.lua
+    // runConformance("strings.lua");
+}
+
+TEST_CASE("StringInterp")
+{
+    runConformance("stringinterp.lua");
 }
 
 TEST_CASE("VarArg")

tests/conformance/stringinterp.lua

@@ -0,0 +1,45 @@
+local function assertEq(left, right)
+	assert(typeof(left) == "string")
+	assert(typeof(right) == "string")
+
+	if left ~= right then
+		error(string.format("%q ~= %q", left, right))
+	end
+end
+
+assertEq(`hello {"world"}`, "hello world")
+
+-- assertEq(`2 + 2 = {2 + 2}`, "2 + 2 = 4")
+
+-- assertEq(`{1} {2} {3} {4} {5} {6} {7}`, "1 2 3 4 5 6 7")
+
+-- local combo = {5, 2, 8, 9}
+-- assert(`The lock combinations are: {table.concat(combo, ", ")}` == "The lock combinations are: 5, 2, 8, 9")
+
+-- assert(`true = {true}` == "true = true")
+
+-- -- INTERP TODO: Syntax error
+-- -- assert(string.find(`{{ "nested braces!" }}`, "table"))
+
+-- local name = "Luau"
+-- assert(`Welcome to {
+-- 	name
+-- }!` == "Welcome to Luau!")
+-- assert(`Welcome to \
+-- {name}!` == "Welcome to\nLuau!")
+
+-- assert(`Escaped brace: \{} ({1})` == "Escaped brace: { (1)")
+-- assert(`Backslash \ that escapes the space is not a part of the string... ({2})` == "Backslash  that escapes the space is not a part of the string... (2)")
+-- assert(`Escaped backslash \\ ({3})` == "Escaped backslash \\ (3)")
+-- assert(`Escaped backtick: \` ({4})` == "Escaped backtick: ` (4)")
+
+-- assert(`Hello {`from inside {"a nested string"}`}` == "Hello from inside a nested string")
+
+-- assert(`1 {`2 {`3 {4}`}`}` == "1 2 3 4")
+
+-- local health = 50
+-- assert(`You have {health}% health` == "You have 50% health")
+
+-- INTERP TODO: Test with shadowing `string` (both as a string and not)
+
+return "OK"

tests/conformance/strings.lua

@@ -60,7 +60,7 @@ assert(#"\0\0\0" == 3)
 assert(#"1234567890" == 10)
 
 assert(string.byte("a") == 97)
-assert(string.byte("á") > 127)
+assert(string.byte("<EFBFBD>") > 127)
 assert(string.byte(string.char(255)) == 255)
 assert(string.byte(string.char(0)) == 0)
 assert(string.byte("\0") == 0)
@@ -75,10 +75,10 @@ assert(string.byte("hi", 9, 10) == nil)
 assert(string.byte("hi", 2, 1) == nil)
 assert(string.char() == "")
 assert(string.char(0, 255, 0) == "\0\255\0")
-assert(string.char(0, string.byte("á"), 0) == "\0á\0")
-assert(string.char(string.byte("ál\0óu", 1, -1)) == "ál\0óu")
-assert(string.char(string.byte("ál\0óu", 1, 0)) == "")
-assert(string.char(string.byte("ál\0óu", -10, 100)) == "ál\0óu")
+assert(string.char(0, string.byte("<EFBFBD>"), 0) == "\0<EFBFBD>\0")
+assert(string.char(string.byte("<EFBFBD>l\0<EFBFBD>u", 1, -1)) == "<EFBFBD>l\0<EFBFBD>u")
+assert(string.char(string.byte("<EFBFBD>l\0<EFBFBD>u", 1, 0)) == "")
+assert(string.char(string.byte("<EFBFBD>l\0<EFBFBD>u", -10, 100)) == "<EFBFBD>l\0<EFBFBD>u")
 assert(pcall(function() return string.char(256) end) == false)
 assert(pcall(function() return string.char(-1) end) == false)
 print('+')
@@ -86,7 +86,7 @@ print('+')
 assert(string.upper("ab\0c") == "AB\0C")
 assert(string.lower("\0ABCc%$") == "\0abcc%$")
 assert(string.rep('teste', 0) == '')
-assert(string.rep('tés\00tê', 2) == 'tés\0têtés\000tê')
+assert(string.rep('t<EFBFBD>s\00t<EFBFBD>', 2) == 't<EFBFBD>s\0t<EFBFBD>t<EFBFBD>s\000t<EFBFBD>')
 assert(string.rep('', 10) == '')
 
 assert(string.reverse"" == "")
@@ -106,12 +106,12 @@ assert(tostring(true) == "true")
 assert(tostring(false) == "false")
 print('+')
 
-x = '"ílo"\n\\'
-assert(string.format('%q%s', x, x) == '"\\"ílo\\"\\\n\\\\""ílo"\n\\')
+x = '"<EFBFBD>lo"\n\\'
+assert(string.format('%q%s', x, x) == '"\\"<EFBFBD>lo\\"\\\n\\\\""<22>lo"\n\\')
 assert(string.format('%q', "\0") == [["\000"]])
 assert(string.format('%q', "\r") == [["\r"]])
-assert(string.format("\0%c\0%c%x\0", string.byte("á"), string.byte("b"), 140) ==
-              "\0á\0b8c\0")
+assert(string.format("\0%c\0%c%x\0", string.byte("<EFBFBD>"), string.byte("b"), 140) ==
+              "\0<EFBFBD>\0b8c\0")
 assert(string.format('') == "")
 assert(string.format("%c",34)..string.format("%c",48)..string.format("%c",90)..string.format("%c",100) ==
        string.format("%c%c%c%c", 34, 48, 90, 100))
@@ -130,7 +130,14 @@ assert(string.format('"-%20s.20s"', string.rep("%", 2000)) ==
 -- longest number that can be formated
 assert(string.len(string.format('%99.99f', -1e308)) >= 100)
 
-assert(loadstring("return 1\n--comentário sem EOL no final")() == 1)
+local function return_one_thing() return "hi" end
+local function return_two_nils() return nil, nil end
+
+assert(string.format("%*", return_one_thing()) == "hi")
+assert(string.format("%* %*", return_two_nils()) == "nil nil")
+assert(pcall(function() string.format("%* %* %*", return_two_nils()) end) == false)
+
+assert(loadstring("return 1\n--coment<6E>rio sem EOL no final")() == 1)
 
 
 assert(table.concat{} == "")
@@ -163,16 +170,16 @@ end
 if not trylocale("collate")  then
   print("locale not supported")
 else
-  assert("alo" < "álo" and "álo" < "amo")
+  assert("alo" < "<EFBFBD>lo" and "<EFBFBD>lo" < "amo")
 end
 
 if not trylocale("ctype") then
   print("locale not supported")
 else
-  assert(string.gsub("áéíóú", "%a", "x") == "xxxxx")
-  assert(string.gsub("áÁéÉ", "%l", "x") == "xÁxÉ")
-  assert(string.gsub("áÁéÉ", "%u", "x") == "áxéx")
-  assert(string.upper"áÁé{xuxu}ção" == "ÁÁÉ{XUXU}ÇÃO")
+  assert(string.gsub("<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>", "%a", "x") == "xxxxx")
+  assert(string.gsub("<EFBFBD><EFBFBD><EFBFBD><EFBFBD>", "%l", "x") == "x<EFBFBD>x<EFBFBD>")
+  assert(string.gsub("<EFBFBD><EFBFBD><EFBFBD><EFBFBD>", "%u", "x") == "<EFBFBD>x<EFBFBD>x")
+  assert(string.upper"<EFBFBD><EFBFBD><EFBFBD>{xuxu}<7D><>o" == "<EFBFBD><EFBFBD><EFBFBD>{XUXU}<7D><>O")
 end
 
 os.setlocale("C")