Struct VmCapabilities 

pub struct VmCapabilities {
    pub can_watch_field_modification: bool,
    pub can_watch_field_access: bool,
    pub can_get_bytecodes: bool,
    pub can_get_synthetic_attribute: bool,
    pub can_get_owned_monitor_info: bool,
    pub can_get_current_contended_monitor: bool,
    pub can_get_monitor_info: bool,
}

What the target JVM says it supports (VirtualMachine.Capabilities).

The seven original capabilities, which is all this command reports. The newer bits — including the ones hot reload depends on — live in VmCapabilitiesNew behind CapabilitiesNew (command 17); until SWAP-1 (#58) nothing here needed them, and this comment said so. Note that JDI’s canGetMethodReturnValues is not a capability bit at all — it is a JDWP version check (≥ 1.6), so get_version answers that one.

Worth asking before a feature that depends on one: a JVM without the capability answers NOT_IMPLEMENTED (99) to the actual command, and “this JVM can’t tell us” is a far more useful report than a bare error code.

Two features deliberately don’t ask, and it is worth knowing which, so the sentence above is not read as a guarantee it does not make: force_early_return (canForceEarlyReturn) and get_source_debug_extension (canGetSourceDebugExtension) both issue their command without checking first, and neither bit is decoded — VmCapabilitiesNew reads through position 18 and names five of those, so 13 (canGetSourceDebugExtension) is read past and 21 (canForceEarlyReturn) is never reached. Both then surface the raw NOT_IMPLEMENTED (99), which is precisely the bare error code this rule exists to improve on. Accepted for now rather than overlooked: adding a bit nothing consults is the mistake IDSizes was deleted for (CLEAN-1, #27), so the bits arrive with the check, not before it. Measured values for the whole CapabilitiesNew vector on Temurin 17.0.20 are in docs/heap-query-measurements.md.

Fields

can_watch_field_modification: bool

can_watch_field_access: bool

can_get_bytecodes: bool

can_get_synthetic_attribute: bool

can_get_owned_monitor_info: bool

Whether owned_monitors will work.

can_get_current_contended_monitor: bool

Whether current_contended_monitor will work.

can_get_monitor_info: bool

Trait Implementations

impl Clone for VmCapabilities

fn clone(&self) -> VmCapabilities

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for VmCapabilities

impl Debug for VmCapabilities

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for VmCapabilities

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for VmCapabilities

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.