[dartfuzz] Fix infinite recursion

Change-Id: Ie758aae5bf2d455b3232eebfb5a2e960041a4520
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127581
Commit-Queue: Fizaa Luthra <fizaaluthra@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>
Reviewed-by: Aart Bik <ajcbik@google.com>

runtime/tools/dartfuzz/dartfuzz.dart

@@ -14,7 +14,7 @@ import 'dartfuzz_type_table.dart';
 // Version of DartFuzz. Increase this each time changes are made
 // to preserve the property that a given version of DartFuzz yields
 // the same fuzzed program for a deterministic random seed.
-const String version = '1.76';
+const String version = '1.77';
 
 // Restriction on statements and expressions.
 const int stmtDepth = 1;
@@ -81,12 +81,21 @@ abstract class Method {
         }, parameters.length, start: 1));
   }
 
+  void disableRecursionScope(Function callback) {
+    final originalState = recursionAllowed;
+    recursionAllowed = false;
+    callback();
+    recursionAllowed = originalState;
+  }
+
   void emitRecursionBaseCase() {
     fuzzer.emitIfStatement(() {
       fuzzer.emit("$recursionDepthParamName >= ");
       fuzzer.emitSmallPositiveInt();
     }, () {
-      fuzzer.emitReturn(terminal: true);
+      // Temporarily set recursionAllowed to false so that we don't have a
+      // recursive call in the return statement of the base case.
+      disableRecursionScope(fuzzer.emitReturn);
       return false;
     });
   }
@@ -140,7 +149,7 @@ abstract class Method {
   final String name;
   final List<DartType> parameters;
   final DartFuzz fuzzer;
-  final bool recursionAllowed;
+  bool recursionAllowed;
 }
 
 /// Class for global methods generated by DartFuzz.
@@ -160,6 +169,9 @@ class FfiMethod extends Method {
   void emitFunctionBody() {
     fuzzer.emitBraceWrapped(() {
       assert(fuzzer.localVars.isEmpty);
+      if (recursionAllowed) {
+        emitRecursionBaseCase();
+      }
       if (fuzzer.emitStatements(0)) {
         fuzzer.emitReturn();
       }
@@ -1071,13 +1083,13 @@ class DartFuzz {
   }
 
   // Emit a return statement.
-  bool emitReturn({bool terminal = false}) {
+  bool emitReturn() {
     List<DartType> proto = getCurrentProto();
     if (proto == null) {
       emitLn('return;');
     } else {
       emitLn('return ', newline: false);
-      emitExpr(0, proto[0], includeSemicolon: true, terminal: terminal);
+      emitExpr(0, proto[0], includeSemicolon: true);
     }
     return false;
   }
@@ -2012,13 +2024,10 @@ class DartFuzz {
 
   // Emit expression.
   void emitExpr(int depth, DartType tp,
-      {RhsFilter rhsFilter,
-      bool includeSemicolon = false,
-      // Setting terminal to true forces the emission of a terminal.
-      bool terminal = false}) {
+      {RhsFilter rhsFilter, bool includeSemicolon = false}) {
     final resetExprStmt = processExprOpen(tp);
     // Continuing nested expressions becomes less likely as the depth grows.
-    if (terminal || (choose(depth + 1) > exprDepth)) {
+    if (choose(depth + 1) > exprDepth) {
       emitTerminal(depth, tp, rhsFilter: rhsFilter);
     } else {
       // Possibly nested expression.