Fix incorrect data consumption for &max-size.

We would previously handle `&size` and `&max-size` almost identical
with the only difference that `&max-size` sets up a slightly larger view
to accomodate a sentinel. In particular, we also used identical code to
set up the position where parsing should resume after such a field.

This was incorrect as it is in general impossible to tell where parsing
continues after a field with `&max-size` since it does not signify a
fixed view like `&size`. In this patch we now compute the next position
for a `&max-size` field by inspecting the limited view to detect how
much data was extracted.

Closes #1668.

spicy/toolchain/src/compiler/codegen/parser-builder.cc

@@ -778,6 +778,11 @@ struct ProductionVisitor
 
                 pb->parseError("parsing not done within &max-size bytes", a->meta());
             });
+
+            // For `&max-size` we use `ncur` to store a view limited and slightly larger than the _permissible_ range,
+            // not the _consumed_ range. Update the value with where we ended up during parsing so we can inspect it
+            // below when setting the position after parsing.
+            ncur = state().cur;
         }
 
         else if ( auto a = AttributeSet::find(field->attributes(), "&size") ) {
@@ -814,8 +819,17 @@ struct ProductionVisitor
             pb->saveParsePosition();
         }
 
-        if ( ncur )
+        if ( ncur ) {
+            // For `&max-size` we use `ncur` to store a view limited and slightly larger than the _permissible_ range,
+            // not the _consumed_ range. We need to manually compute the actually consumed range from where we ended
+            // parsing in the limited view. We update the value stored in `ncur` so it can be updated below.
+            if ( AttributeSet::find(field->attributes(), "&max-size") )
+                ncur = builder::memberCall(state().cur, "advance",
+                                           {builder::difference(builder::memberCall(*ncur, "offset", {}),
+                                                                builder::memberCall(state().cur, "offset", {}))});
+
             builder()->addAssign(state().cur, *ncur);
+        }
 
         if ( ! meta.container() ) {
             if ( pb->isEnabledDefaultNewValueForField() && state().literal_mode == LiteralMode::Default )

tests/Baseline/spicy.types.unit.field-max-size/output

@@ -2,6 +2,6 @@
 done, [$xs=b"\x00"]
 done, [$xs=b"\x01\x00"]
 error, [$xs=(not set)]
-[error] terminating with uncaught exception of type spicy::rt::ParseError: parsing not done within &max-size bytes (<...>/field-max-size.spicy:15:40-15:56)
+[error] terminating with uncaught exception of type spicy::rt::ParseError: parsing not done within &max-size bytes (<...>/field-max-size.spicy:16:40-16:56)
 error, [$xs=b"\x01\x01\x01"]
-[error] terminating with uncaught exception of type spicy::rt::ParseError: end-of-data reached before &until-including expression found (<...>/field-max-size.spicy:15:32-15:38)
+[error] terminating with uncaught exception of type spicy::rt::ParseError: end-of-data reached before &until-including expression found (<...>/field-max-size.spicy:16:32-16:38)

tests/Baseline/spicy.types.unit.field-max-size/output2

@@ -0,0 +1,11 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+Mini::X {
+  use_max_size: True
+  xs: 
+  rest: BC
+}
+Mini::X {
+  use_max_size: False
+  xs: 
+  rest: BC
+}

tests/spicy/types/unit/field-max-size.spicy

@@ -1,14 +1,15 @@
-# @TEST-EXEC: spicyc -j -d %INPUT -o test.hlto
-# @TEST-EXEC: printf '\000' | spicy-driver -d test.hlto >>output 2>&1
-# @TEST-EXEC: printf '\001\000' | spicy-driver -d test.hlto >>output 2>&1
-# @TEST-EXEC-FAIL: printf '\001\001\000' | spicy-driver -d test.hlto >>output 2>&1
-# @TEST-EXEC-FAIL: printf '\001\001\001\000' | spicy-driver -d test.hlto >>output 2>&1
-# @TEST-EXEC: btest-diff output
-#
 # @TEST-DOC: Validate effects of field-level `&max-size` attribute
+#
+# @TEST-EXEC: spicyc -j -d %INPUT -o test.hlto
 
 module Mini;
 
+# @TEST-EXEC: printf '\000' | spicy-driver -d test.hlto -p Mini::Test >>output 2>&1
+# @TEST-EXEC: printf '\001\000' | spicy-driver -d test.hlto -p Mini::Test >>output 2>&1
+# @TEST-EXEC-FAIL: printf '\001\001\000' | spicy-driver -d test.hlto -p Mini::Test >>output 2>&1
+# @TEST-EXEC-FAIL: printf '\001\001\001\000' | spicy-driver -d test.hlto -p Mini::Test >>output 2>&1
+# @TEST-EXEC: btest-diff output
+
 const MaxSize = 2;
 
 public type Test = unit {
@@ -17,3 +18,19 @@ public type Test = unit {
     on %done { print "done", self; }
     on %error { print "error", self; }
 };
+
+# Check that `&max-size` has no effect on how much data is consumed. This is a regression test for #1668.
+# @TEST-EXEC: printf '\001_BC' | spicy-dump -d test.hlto -p Mini::X >>output2 2>&1
+# @TEST-EXEC: printf '\000_BC' | spicy-dump -d test.hlto -p Mini::X >>output2 2>&1
+# @TEST-EXEC: btest-diff output2
+
+public type X = unit {
+    use_max_size: uint8 &convert=cast<bool>($$);
+
+    switch (self.use_max_size) {
+        True -> xs: bytes &until=b"_" &max-size=1;
+        False -> xs: bytes &until=b"_";
+    };
+
+    rest: bytes &eod;
+};