Handle formatting of parts of formatted interpolated string

Analysis/src/Autocomplete.cpp

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Autocomplete.h"
 
+#include "Luau/Ast.h"
 #include "Luau/AstQuery.h"
 #include "Luau/BuiltinDefinitions.h"
 #include "Luau/Frontend.h"
@@ -1238,6 +1239,12 @@ static bool stringPartOfInterpString(const AstNode* node, Position position)
     return true;
 }
 
+static bool isSimpleInterpolatedString(const AstNode* node)
+{
+    const AstExprInterpString* interpString = node->as<AstExprInterpString>();
+    return interpString != nullptr && interpString->expressions.size == 0;
+}
+
 static std::optional<AutocompleteEntryMap> autocompleteStringParams(const SourceModule& sourceModule, const ModulePtr& module,
     const std::vector<AstNode*>& nodes, Position position, StringCompletionCallback callback)
 {
@@ -1246,7 +1253,8 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(const Source
         return std::nullopt;
     }
 
-    if (!nodes.back()->is<AstExprConstantString>() && !stringPartOfInterpString(nodes.back(), position) && !nodes.back()->is<AstExprError>())
+    if (!nodes.back()->is<AstExprConstantString>() && !isSimpleInterpolatedString(nodes.back()) && !nodes.back()->is<AstExprInterpString>() &&
+        !nodes.back()->is<AstExprError>())
     {
         return std::nullopt;
     }
@@ -1490,7 +1498,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
     {
         return {*ret, ancestry, AutocompleteContext::String};
     }
-    else if (node->is<AstExprConstantString>() || stringPartOfInterpString(node, position))
+    else if (node->is<AstExprConstantString>() || isSimpleInterpolatedString(node))
     {
         AutocompleteEntryMap result;
 
@@ -1516,6 +1524,13 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
 
         return {result, ancestry, AutocompleteContext::String};
     }
+    else if (stringPartOfInterpString(node, position))
+    {
+        // We're not a simple interpolated string, we're something like `a{"b"}@1`, and we
+        // can't know what to format to
+        AutocompleteEntryMap map;
+        return {map, ancestry, AutocompleteContext::String};
+    }
 
     if (node->is<AstExprConstantNumber>())
         return {};

Ast/src/Parser.cpp

@@ -2692,17 +2692,21 @@ AstExpr* Parser::parseInterpString()
             break;
         }
 
+        bool errorWhileChecking = false;
+
         switch (lexer.current().type)
         {
         case Lexeme::InterpStringMid:
         case Lexeme::InterpStringEnd:
         {
+            errorWhileChecking = true;
             nextLexeme();
             expressions.push_back(reportExprError(endLocation, {}, "Malformed interpolated string, expected expression inside '{}'"));
             break;
         }
         case Lexeme::BrokenString:
         {
+            errorWhileChecking = true;
             nextLexeme();
             expressions.push_back(reportExprError(endLocation, {}, "Malformed interpolated string, did you forget to add a '`'?"));
             break;
@@ -2711,6 +2715,11 @@ AstExpr* Parser::parseInterpString()
             expressions.push_back(parseExpr());
         }
 
+        if (errorWhileChecking)
+        {
+            break;
+        }
+
         switch (lexer.current().type)
         {
         case Lexeme::InterpStringBegin:

tests/Autocomplete.test.cpp

@@ -2761,6 +2761,27 @@ TEST_CASE_FIXTURE(ACFixture, "autocomplete_interpolated_string_expression_with_c
     CHECK_EQ(ac.context, AutocompleteContext::Expression);
 }
 
+TEST_CASE_FIXTURE(ACFixture, "autocomplete_interpolated_string_as_singleton")
+{
+    ScopedFastFlag sff{"LuauInterpolatedStringBaseSupport", true};
+
+    check(R"(
+        --!strict
+        local function f(a: "cat" | "dog") end
+
+        f(`@1`)
+        f(`uhhh{'try'}@2`)
+    )");
+
+    auto ac = autocomplete('1');
+    CHECK(ac.entryMap.count("cat"));
+    CHECK_EQ(ac.context, AutocompleteContext::String);
+
+    ac = autocomplete('2');
+    CHECK(ac.entryMap.empty());
+    CHECK_EQ(ac.context, AutocompleteContext::String);
+}
+
 TEST_CASE_FIXTURE(ACFixture, "autocomplete_explicit_type_pack")
 {
     check(R"(