This commit introduces the following changes.
1) It adds a new Spring @NonNull annotation which allows to apply
@NonNullApi semantic on a specific element, like @Nullable does.
Combined with @Nullable, it allows partial null-safety support when
package granularity is too broad.
2) @Nullable and @NonNull can apply to ElementType.TYPE_USE in order
to be used on generic type arguments (SPR-15942).
3) Annotations does not apply to ElementType.TYPE_PARAMETER anymore
since it is not supported yet (applicability for such use case is
controversial and need to be discussed).
4) @NonNullApi does not apply to ElementType.FIELD anymore since in a
lot of use cases (private, protected) it is not part for the public API
+ its usage should remain opt-in. A dedicated @NonNullFields annotation
has been added in order to set fields default to non-nullable.
5) Updated Javadoc and reference documentation.
Issue: SPR-15756
This commits extends nullability declarations to the field level, formalizing the interaction between methods and their underlying fields and therefore avoiding any nullability mismatch.
Issue: SPR-15720
Beyond just formally declaring the current behavior, this revision actually enforces non-null behavior in selected signatures now, not tolerating null values anymore when not explicitly documented. It also changes some utility methods with historic null-in/null-out tolerance towards enforced non-null return values, making them a proper citizen in non-null assignments.
Some issues are left as to-do: in particular a thorough revision of spring-test, and a few tests with unclear failures (ignored as "TODO: NULLABLE") to be sorted out in a follow-up commit.
Issue: SPR-15540
This commit introduces 2 new @Nullable and @NonNullApi
annotations that leverage JSR 305 (dormant but available via
Findbugs jsr305 dependency and already used by libraries
like OkHttp) meta-annotations to specify explicitly
null-safety of Spring Framework parameters and return values.
In order to avoid adding too much annotations, the
default is set at package level with @NonNullApi and
@Nullable annotations are added when needed at parameter or
return value level. These annotations are intended to be used
on Spring Framework itself but also by other Spring projects.
@Nullable annotations have been introduced based on Javadoc
and search of patterns like "return null;". It is expected that
nullability of Spring Framework API will be polished with
complementary commits.
In practice, this will make the whole Spring Framework API
null-safe for Kotlin projects (when KT-10942 will be fixed)
since Kotlin will be able to leverage these annotations to
know if a parameter or a return value is nullable or not. But
this is also useful for Java developers as well since IntelliJ
IDEA, for example, also understands these annotations to
generate warnings when unsafe nullable usages are detected.
Issue: SPR-15540
Until this change a single classloader was used to load
all compiled SpEL expressions. This meant in a context where an
expression was repeatedly flipping between compiled and interpreted
mode (which can happen if in MIXED mode compilation and changing
the context around the evaluation) the classloader would continually
load a new compiled version but not orphan the old compiled version.
This eventually uses up all the memory as the number of classes
is ever increasing.
With this change classloaders are used to load 100 compiled
expressions. The 101st will be loaded by a new one. Orphaning the
old classloader means if an expression is ever recompiled there
is more likely to be no anchored references left to the older
compiled form and it can be GC'd. In the MIXED situation above it
should help alleviate the problem of older classes never being
candidates for GC.
Issue: SPR-15460
Without this fix the compiled version of elvis
actual behaved differently to the interpreted version
if the value being queried was an empty string. This
is now fixed. It also now correctly handles the
query value being a primitive and addresses the
findings of SPR-15192 where some type inferencing
logic was trying to be too clever, that code has
been deleted.
Issue: SPR-15192
For SPR-14863 we need to adjust the code generation for OpNE
to use !x.equals(y) rather than x!=y. There are also further
cases in the equalityCheck() code in Operator that were not
being handled in the compilation case (when comparators are
used for example). This latter issue also affects OpEQ.
Rather than add yet more bytecode generation, both OpNE and
OpEQ generateCode() methods have been simplified. The
generated code now delegates to equalityCheck() in Operator
which is exactly what the interpreted case does.
This ensures that the compiled code continues to behave just
like the interpreted case. It ensures changes to the interpreted
case are automatically picked up for the compiled case. It
makes the bytecode generation simpler.
The benefit of compilation of SpEL expressions is to avoid
slow reflective calls - that doesn't apply for a basic
(in)equality test so there is no need to go crazy in bytecode
gen.
Issue: SPR-14863
