Accurately enumerate all control flow states

Analysis/include/Luau/ControlFlow.h

@@ -14,9 +14,24 @@ enum class ControlFlow
     None = 0b00001,
     Returns = 0b00010,
     Throws = 0b00100,
-    Break = 0b01000,    // Currently unused.
+    Breaks = 0b01000,
-    Continue = 0b10000, // Currently unused.
+    Continues = 0b10000,
+
+    // Returns OR Throws (e.g. if predicate then return else error() end)
+    MixedFunctionExit = 0b100000,
+
+    // Breaks OR Continues (e.g. if predicate then break else continue end)
+    MixedLoopExit = 0b1000000,
+
+    // Exits a loop OR function (e.g. if prediate then continue else return end)
+    MixedExit = 0b10000000,
 };
+// Bitmask of all control flows which exit the nearest function scope
+#define FunctionExitControlFlows ControlFlow::Returns | ControlFlow::Throws | ControlFlow::MixedFunctionExit
+// Bitmask of all control flows which exit the nearest loop scope
+#define LoopExitControlFlows ControlFlow::Breaks | ControlFlow::Continues | ControlFlow::MixedLoopExit
+// Bitmask of all control flows which exit the nearest function or loop scopes
+#define ExitingControlFlows ControlFlow::Returns | ControlFlow::Throws | ControlFlow::Breaks | ControlFlow::Continues | ControlFlow::MixedFunctionExit | ControlFlow::MixedLoopExit | ControlFlow::MixedExit
 
 inline ControlFlow operator&(ControlFlow a, ControlFlow b)
 {

Analysis/src/ConstraintGraphBuilder.cpp

@@ -24,6 +24,7 @@ LUAU_FASTINT(LuauCheckRecursionLimit);
 LUAU_FASTFLAG(DebugLuauLogSolverToJson);
 LUAU_FASTFLAG(DebugLuauMagicTypes);
 LUAU_FASTFLAG(LuauParseDeclareClassIndexer);
+LUAU_FASTFLAG(LuauLoopControlFlowAnalysis);
 
 namespace Luau
 {
@@ -536,11 +537,14 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStat* stat)
         return visit(scope, s);
     else if (auto s = stat->as<AstStatRepeat>())
         return visit(scope, s);
-    else if (stat->is<AstStatBreak>() || stat->is<AstStatContinue>())
+    else if (stat->is<AstStatBreak>())
-    {
+        return FFlag::LuauLoopControlFlowAnalysis
-        // Nothing
+            ? ControlFlow::Breaks
-        return ControlFlow::None; // TODO: ControlFlow::Break/Continue
+            : ControlFlow::None;
-    }
+    else if (stat->is<AstStatContinue>())
+        return FFlag::LuauLoopControlFlowAnalysis
+            ? ControlFlow::Continues
+            : ControlFlow::None;
     else if (auto r = stat->as<AstStatReturn>())
         return visit(scope, r);
     else if (auto e = stat->as<AstStatExpr>())
@@ -1066,20 +1070,60 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatIf* ifSt
     ScopePtr elseScope = childScope(ifStatement->elsebody ? ifStatement->elsebody : ifStatement, scope);
     applyRefinements(elseScope, ifStatement->elseLocation.value_or(ifStatement->condition->location), refinementArena.negation(refinement));
 
+    const ControlFlow guardClauseFlows = FFlag::LuauLoopControlFlowAnalysis
+        ? ExitingControlFlows
+        : ControlFlow::Returns | ControlFlow :: Throws;
+
     ControlFlow thencf = visit(thenScope, ifStatement->thenbody);
     ControlFlow elsecf = ControlFlow::None;
     if (ifStatement->elsebody)
         elsecf = visit(elseScope, ifStatement->elsebody);
 
-    if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && elsecf == ControlFlow::None)
+    if (matches(thencf, guardClauseFlows) && elsecf == ControlFlow::None)
         scope->inheritRefinements(elseScope);
-    else if (thencf == ControlFlow::None && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+    else if (thencf == ControlFlow::None && matches(elsecf, guardClauseFlows))
         scope->inheritRefinements(thenScope);
 
-    if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+    if (FFlag::LuauLoopControlFlowAnalysis)
-        return ControlFlow::Returns;
+    {
-    else
+        if (thencf == elsecf)
+        {
+            return thencf;
+        }
+        if (
+            matches(thencf, FunctionExitControlFlows)
+            && matches(elsecf, FunctionExitControlFlows)
+        )
+        {
+            return ControlFlow::MixedFunctionExit;
+        }
+        if (
+            matches(thencf, LoopExitControlFlows)
+            && matches(elsecf, LoopExitControlFlows)
+        )
+        {
+            return ControlFlow::MixedLoopExit;
+        }
+        if (
+            matches(thencf, ExitingControlFlows)
+            && matches(elsecf, ExitingControlFlows)
+        )
+        {
+            return ControlFlow::MixedExit;
+        }
         return ControlFlow::None;
+    }
+    else
+    {
+        if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+        {
+            return ControlFlow::Returns;
+        }
+        else
+        {
+            return ControlFlow::None;
+        }
+    }
 }
 
 static bool occursCheck(TypeId needle, TypeId haystack)

Analysis/src/TypeInfer.cpp

@@ -366,11 +366,14 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStat& program)
         return check(scope, *while_);
     else if (auto repeat = program.as<AstStatRepeat>())
         return check(scope, *repeat);
-    else if (program.is<AstStatBreak>() || program.is<AstStatContinue>())
+    else if (program.is<AstStatBreak>())
-    {
+        return FFlag::LuauLoopControlFlowAnalysis
-        // Nothing to do
+            ? ControlFlow::Breaks
-        return ControlFlow::None;
+            : ControlFlow::None;
-    }
+    else if (program.is<AstStatContinue>())
+        return FFlag::LuauLoopControlFlowAnalysis
+            ? ControlFlow::Continues
+            : ControlFlow::None;
     else if (auto return_ = program.as<AstStatReturn>())
         return check(scope, *return_);
     else if (auto expr = program.as<AstStatExpr>())
@@ -763,22 +766,62 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatIf& statement
         ScopePtr elseScope = childScope(scope, statement.elsebody ? statement.elsebody->location : statement.location);
         resolve(result.predicates, elseScope, false);
 
+        const ControlFlow guardClauseFlows = FFlag::LuauLoopControlFlowAnalysis
+            ? ExitingControlFlows
+            : ControlFlow::Returns | ControlFlow :: Throws;
+
         ControlFlow thencf = check(thenScope, *statement.thenbody);
         ControlFlow elsecf = ControlFlow::None;
         if (statement.elsebody)
             elsecf = check(elseScope, *statement.elsebody);
 
-        if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && elsecf == ControlFlow::None)
+        if (matches(thencf, guardClauseFlows) && elsecf == ControlFlow::None)
             scope->inheritRefinements(elseScope);
-        else if (thencf == ControlFlow::None && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+        else if (thencf == ControlFlow::None && matches(elsecf, guardClauseFlows))
             scope->inheritRefinements(thenScope);
 
-        if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+        if (FFlag::LuauLoopControlFlowAnalysis)
-            return ControlFlow::Returns;
+        {
-        else
+            if (thencf == elsecf)
+            {
+                return thencf;
+            }
+            if (
+                matches(thencf, FunctionExitControlFlows)
+                && matches(elsecf, FunctionExitControlFlows)
+            )
+            {
+                return ControlFlow::MixedFunctionExit;
+            }
+            if (
+                matches(thencf, LoopExitControlFlows)
+                && matches(elsecf, LoopExitControlFlows)
+            )
+            {
+                return ControlFlow::MixedLoopExit;
+            }
+            if (
+                matches(thencf, ExitingControlFlows)
+                && matches(elsecf, ExitingControlFlows)
+            )
+            {
+                return ControlFlow::MixedExit;
+            }
             return ControlFlow::None;
         }
         else
+        {
+            if (matches(thencf, ControlFlow::Returns | ControlFlow::Throws) && matches(elsecf, ControlFlow::Returns | ControlFlow::Throws))
+            {
+                return ControlFlow::Returns;
+            }
+            else
+            {
+                return ControlFlow::None;
+            }
+        }
+    }
+    else
     {
         check(thenScope, *statement.thenbody);