@@ -43,6 +43,7 @@ pub struct SystemMeta {
4343 is_send : bool ,
4444 has_deferred : bool ,
4545 pub ( crate ) last_run : Tick ,
46+ warn_policy : WarnPolicy ,
4647 #[ cfg( feature = "trace" ) ]
4748 pub ( crate ) system_span : Span ,
4849 #[ cfg( feature = "trace" ) ]
@@ -59,6 +60,7 @@ impl SystemMeta {
5960 is_send : true ,
6061 has_deferred : false ,
6162 last_run : Tick :: new ( 0 ) ,
63+ warn_policy : WarnPolicy :: Once ,
6264 #[ cfg( feature = "trace" ) ]
6365 system_span : info_span ! ( "system" , name = name) ,
6466 #[ cfg( feature = "trace" ) ]
@@ -75,6 +77,7 @@ impl SystemMeta {
7577 /// Sets the name of of this system.
7678///
7779/// Useful to give closure systems more readable and unique names for debugging and tracing.
80+ #[ inline]
7881 pub fn set_name ( & mut self , new_name : impl Into < Cow < ' static , str > > ) {
7982 let new_name: Cow < ' static , str > = new_name. into ( ) ;
8083 #[ cfg( feature = "trace" ) ]
@@ -108,9 +111,70 @@ impl SystemMeta {
108111
109112 /// Marks the system as having deferred buffers like [`Commands`](`super::Commands`)
110113/// This lets the scheduler insert [`apply_deferred`](`crate::prelude::apply_deferred`) systems automatically.
114+ #[ inline]
111115 pub fn set_has_deferred ( & mut self ) {
112116 self . has_deferred = true ;
113117 }
118+
119+ /// Changes the warn policy.
120+ #[ inline]
121+ pub fn set_warn_policy ( & mut self , warn_policy : WarnPolicy ) {
122+ self . warn_policy = warn_policy;
123+ }
124+
125+ /// Advances the warn policy after validation failed.
126+ #[ inline]
127+ pub fn advance_warn_policy ( & mut self ) {
128+ self . warn_policy . advance ( ) ;
129+ }
130+
131+ /// Emits a warning about inaccessible system param if policy allows it.
132+ #[ inline]
133+ pub fn try_warn < P > ( & self )
134+ where
135+ P : SystemParam ,
136+ {
137+ self . warn_policy . try_warn :: < P > ( & self . name ) ;
138+ }
139+ }
140+
141+ /// State machine for emitting warnings when [system params are invalid](System::validate_param).
142+ #[ derive( Clone , Copy ) ]
143+ pub enum WarnPolicy {
144+ /// No warning should ever be emitted.
145+ Never ,
146+ /// The warning will be emitted once and status will update to [`Self::Never`].
147+ Once ,
148+ /// The warning will be emitted every time.
149+ Always ,
150+ }
151+
152+ impl WarnPolicy {
153+ /// Advances the warn policy after validation failed.
154+ #[ inline]
155+ fn advance ( & mut self ) {
156+ * self = match self {
157+ Self :: Never => Self :: Never ,
158+ Self :: Once => Self :: Never ,
159+ Self :: Always => Self :: Always ,
160+ } ;
161+ }
162+
163+ /// Emits a warning about inaccessible system param if policy allows it.
164+ #[ inline]
165+ fn try_warn < P > ( & self , name : & str )
166+ where
167+ P : SystemParam ,
168+ {
169+ if matches ! ( self , Self :: Never ) {
170+ return ;
171+ }
172+ bevy_utils:: tracing:: warn!(
173+ "System {0} will not run because it requested inaccessible system parameter {1}" ,
174+ name,
175+ std:: any:: type_name:: <P >( )
176+ ) ;
177+ }
114178}
115179
116180// TODO: Actually use this in FunctionSystem. We should probably only do this once Systems are constructed using a World reference
@@ -657,9 +721,13 @@ where
657721 }
658722
659723 #[ inline]
660- unsafe fn validate_param_unsafe ( & self , world : UnsafeWorldCell ) -> bool {
724+ unsafe fn validate_param_unsafe ( & mut self , world : UnsafeWorldCell ) -> bool {
661725 let param_state = self . param_state . as_ref ( ) . expect ( Self :: PARAM_MESSAGE ) ;
662- F :: Param :: validate_param ( param_state, & self . system_meta , world)
726+ let is_valid = unsafe { F :: Param :: validate_param ( param_state, & self . system_meta , world) } ;
727+ if !is_valid {
728+ self . system_meta . advance_warn_policy ( ) ;
729+ }
730+ is_valid
663731 }
664732
665733 #[ inline]
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