Don't warn if no relevant targets in glob or --changed. (#14904)

In these cases, the user intent is likely "if there are relevant
targets, act on them", so warning is just annoying.

However we still want to retain the warning if the user provided
literal addresses, filesystem specs, or no specs at all.

[ci skip-rust]

[ci skip-build-wheels]

src/python/pants/base/specs.py

@@ -333,6 +333,7 @@ def __bool__(self) -> bool:
 class Specs:
     address_specs: AddressSpecs
     filesystem_specs: FilesystemSpecs
+    from_change_detection: bool = False
 
     @property
     def provided(self) -> bool:

src/python/pants/engine/internals/graph.py

@@ -1320,7 +1320,18 @@ async def find_valid_field_sets_for_target_roots(
         )
         if request.no_applicable_targets_behavior == NoApplicableTargetsBehavior.error:
             raise no_applicable_exception
-        if request.no_applicable_targets_behavior == NoApplicableTargetsBehavior.warn:
+        # We squelch the warning if the specs came from change detection or only from address globs,
+        # since in that case we interpret the user's intent as "if there are relevant matching
+        # targets, act on them". But we still want to warn if the specs were literal, or empty.
+        empty_ok = specs.from_change_detection or (
+            specs.address_specs.globs
+            and not specs.address_specs.literals
+            and not specs.filesystem_specs
+        )
+        if (
+            request.no_applicable_targets_behavior == NoApplicableTargetsBehavior.warn
+            and not empty_ok
+        ):
             logger.warning(str(no_applicable_exception))
 
     result = TargetRootsToFieldSets(targets_to_applicable_field_sets)

src/python/pants/init/specs_calculator.py

@@ -75,7 +75,11 @@ def calculate_specs(
                 parameters=address_input.parameters,
             )
         )
-    return Specs(AddressSpecs(address_specs, filter_by_global_options=True), FilesystemSpecs([]))
+    return Specs(
+        AddressSpecs(address_specs, filter_by_global_options=True),
+        FilesystemSpecs([]),
+        from_change_detection=True,
+    )
 
 
 def rules():