Merge pull request #1696 from evoskuil/master

Program initialize is_prevalid() insufficiently prioritized.

Author: evoskuil

include/bitcoin/system/impl/machine/interpreter_run.ipp

@@ -38,7 +38,6 @@ TEMPLATE
 code CLASS::
 run() NOEXCEPT
 {
-    // Enforce initial limits, determine early success or failure.
     if (const auto ec = state::initialize())
         return ec;
 

include/bitcoin/system/impl/machine/program.ipp

@@ -61,25 +61,25 @@ initialize() const NOEXCEPT
     const auto bip141 = is_enabled(flags::bip141_rule);
     const auto bip342 = is_enabled(flags::bip342_rule);
 
-    // Apply stack element limit (520) to initial witness [bip141][bip342].
-    if (bip141 && witness_ && !chain::witness::is_push_size(*witness_))
-        return error::invalid_witness_stack;
+    // Succeed if any success code, overrides all codes and errors [bip342].
+    if (bip342 && script_->is_prevalid())
+        return error::prevalid_script;
 
-    // Script size limit (10,000) [0.3.7+], removed [bip342].
-    if (!bip342 && nops && script_->is_oversized())
-        return error::invalid_script_size;
+    // Fail if last op is underflow (same behavior as prefail, invalid code).
+    if (script_->is_underflow())
+        return error::invalid_script;
 
-    // Stacks element limit (1,000) applied to initial stack [bip342].
+    // Stack limit (1,000) applied to initial stack [bip342].
     if (bip342 && is_stack_overflow())
         return error::invalid_stack_size;
 
-    // Succeed if any success code, one overrides all codes [bip342].
-    if (bip342 && script_->is_prevalid())
-        return error::prevalid_script;
+    // Apply stack element limit (520) to initial witness [bip342|bip141].
+    if ((bip342 || bip141) && witness_ && !chain::witness::is_push_size(*witness_))
+        return error::invalid_witness_stack;
 
-    // Fail if last op underflow, lower priority than success codes [bip342].
-    if (script_->is_underflow())
-        return error::invalid_script;
+    // Script size limit (10,000) [0.3.7+], removed [bip342].
+    if (!bip342 && nops && script_->is_oversized())
+        return error::invalid_script_size;
 
     // Fail if any op invalid (invalid codes reduced in tapscript).
     // Should be after underflow check since underflow is also an invalid op.