v0.3.0 is another incremental-ish release with a bunch of new features, many on the server end but including a bunch of general-purpose improvements. It includes several things that are breaking changes in the semantic-versioning sense, but you may find that not much breaks in your actual app. (For example, no code in any of the the three starter templates needed to change.)

New Features and Small Fixes

General

No longer necessary to import __Props types for components; you can just use app::MyComponent; instead of app::{MyComponent, MyComponentProps};
#[slot] syntax to define typed component children.
Typed events in window_event_listener
Optional event listeners with HtmlElement::optional_event
Adds style: syntax in the view macro to set individual styles, much like class: sets individual classes
Simplify work with resources by adding a Resource::update method to reactively update current value.
expect_context::<T>(cx) shorthand for use_context::<T>(cx).unwrap()

Server

Support for server functions that use GET requests (with either URL or CBOR encoding), for easier caching.
extract helper to directly use Actix extractors in a server function.
Allow more complex data like structs and Vec<_> as server function arguments (anything that can be de/serialized by serde_qs)
Support for rendering a <Route/> in response to additional HTTP methods/verbs, e.g., the classic PHP/multi-page-app style in which a POST request can be sent to a page and it will render a response. (See methods prop.)
Support for SsrMode::PartiallyBlocked which works like out-of-order streaming but replaces the HTML for any “blocked” fragments on the server. Improves UX when JS is disabled.

Developer Experience and Ergonomics

Top-to-bottom integration with the tracing crate
Adding some "real-time docs" via several runtime warnings and compile-time errors to prevent common bugs (for example, using leptos_meta with no features enabled or accidentally ending the view a component returns with a semicolon, meaning it renders nothing)

Performance

Improve performance of Axum integration by spawning requests into a local threadpool.
Improve performance of router on the server side by caching branch generation.
Performance improvements in the reactive system and renderer, and closing a memory leak in <Suspense/>/<Transition/>.

And as always...

Lots of bug fixes! Full changelog below.

Breaking Changes

&'a str can no longer be directly rendered as a view: add .to_string() to effected variables. (Previously, all &str were converted to String by the renderer; using Cow<'static, str> now allows &'static str to be rendered without the additional allocation, at the cost of requiring the conversion of &str to String to be more explicit.)
window_event_listener now takes a typed event (like ev::keypress). Use window_event_listener_untyped for the old behavior.
When deriving Params to use typed router search/params, the FromStr error for any type needs to be Send + Sync so they are ErrorBoundary compatible
Generics in create_slice have changed to allow different input types for getter/setter; only relevant if (for some reason?) you were specifying them manually.
Exact interfaces for a few public-but-rarely-needed functions in the server integrations have changed.

What's Changed

Fix server functions default macro on stable by @Demonthos in #784
docs: add runtime "strict mode" checks that warn if you’re non-reactively accessing a value by @gbj in #786
fix: warnings about untracked signal access in <Router/> by @gbj in #790
Remove unused fs dependency from leptos_config by @valeth in #787
fix: untrack should disable warnings about untracked reads by @gbj in #791
fix: nested <Suspense/> by @gbj in #781
docs: <Form/> component by @gbj in #792
Fix server functions with non-copy server contexts by @Demonthos in #785
fix: unused warning on cx in server functions by @markcatley in #794
docs: warn if you are using leptos_meta without features by @gbj in #797
fix: warning in Cargo.toml by @markcatley in #800
feat: Add ability to include options to event listeners by @Ofenhed in #799
fix: fixes #802 as a temporary measure without resorting to #803 yet by @gbj in #804
fix: prevent router panic on root-level <Redirect/> during route list generation by @gbj in #801
Reduce size of RuntimeId when slotmap is not used by @novacrazy in #805
fix: unused warning in reactive signal diagnostics by @markcatley in #807
Add the ability for server fns to be submitted via GET requests by @benwis in #789
chore: fix unused variable warning in property now that it's not memoized by @gbj in #810
Optimize Runtime::mark_dirty by @novacrazy in #808
Optimize memory usage of update methods by @novacrazy in #809
fix: correctly escape HTML special characters in text nodes during SSR by @gbj in #812
Publish book ci by @bram209 in #817
remove Leptos guide link by @bram209 in #818
docs: add sandbox links and max height by @gbj in #824
fix: correctly pass server fn errors to client by @gbj in #822
fix: server functions with url as argument name (closes issue #823) by @gbj in #825
chore: deny warnings on github actions by @markcatley in #814
Use local pools for axum handlers by @akarras in #815
tests: update benchmarks by @gbj in #827
feat: make __Props imports unnecessary (closes #746) by @gbj in #828
Various optimizations, size reductions and stability improvements by @novacrazy in #831
Fix leaked memo nodes by @novacrazy in #841
[Fix] Correct broken MaybeSignal link by @hoangph271 in #840
feat: rustls feature for reqwest and any other relevant dependencies by @gbj in #842
fix: don't entity-encode HTML special characters inside <script> or <style> (closes #837) by @gbj in #846
feat: allow multiple HTTP request methods/verbs by @gbj in #695
[WIP] Trigger prototype by @novacrazy in #838
fix static text nodes with curly braces in SSR by @gbj in #849
docs: emit error when trying to combine global class and dynamic class in a bugged way by @gbj in #850
fix: custom events in SSR mode by @gbj in #852
fix: Strip & from the end of params queries by @mondeja in #854
fix: match statement in leptos book by @chroth7 in #860
Fix the counter without macros test by @agilarity in #863
feat: add ability to set node_ref and pass additional attributes to <Form/> and friends by @gbj in #853
Fixed typo in life cycle docs by @Stackingttv in #869
examples: fix error handling in fetch example by @gbj in #870
feat: add the ability to specify animations on route transitions by @gbj in #736
[fix] updated nix flakes lock files on session auth axum examples by @mustafasegf in #872
docs: Add per-project toolchain override readme by @kamilogorek in #876
feat: add non-animation base classes to <AnimatedOutlet/> and <AnimatedRoutes/> by @gbj in #877
Use override key, if available, for server function calling by @snapbug in #878
feat: add expect_context function by @markcatley in #864
fix: rendering error in SSR InOrder/Async Mode by @hjin-me in #879
Split counter without macros web test by @agilarity in #884
fix: dispose of scope when server fns return error by @gbj in #888
perf: tiny optimization on primitive child values by @gbj in #887
chore(readme): add link to Matrix bridge by @filipdutescu in #894
Fixes #890 that was using OnceLock, which is nightly only, by adding the once_cell crate as a dependency. by @OvermindDL1 in #891
This should solve ParamsMap / LinearMap serde serialization and deserialization #892 by @dgsantana in #895
feat: add ability to mutate resources by @gbj in #886
fix: erroneous non-reactive access warning in undelegated events by @gbj in #900
perf: improve router performance on server by calculating route branches once by @gbj in #898
Added get_untracked for node_ref. by @dgsantana in #902
Use cargo make to run tests for examples by @agilarity in #904
Add a window event listener with a callback that receives an event that has been cast to its non-generic type. by @loganbnielsen in #910
docs: compile error on mutually-exclusive features by @gbj in #911
fix: issue with ordering of class attribute and class=("fancy-name-200", true) (closes #907) by @gbj in #914
change: add window_event_listener_untyped and deprecate window_event_listener pending 0.3.0 by @gbj in #913
feat: add slots by @yuuma03 in #909
examples: fix broken counters tests by @gbj in #915
fix some issues with animated routing by @gbj in #889
fix: panic when creating nested StoredValue by @gbj in #920
Tracing Updates by @benwis in #908
docs: fixed a minor typo in async readme by @escwxyz in #921
docs: removed extra unused code blocks in form.md by @escwxyz in #923
docs: fixed typo in interlude_styling.md by @escwxyz in #924
fix: features related compile error by @agilarity in #919
fix: allow nested slots by @yuuma03 in #928
docs: add some content on server-side rendering by @gbj in #930
chore: specify dependency version for cached by @rodrigc in #929
Remove need for LEPTOS_OUTPUT_NAME env var after compilation by @benwis in #899
Added (potentially broken) timer example by @bluenote10 in #925
Link to actual type instead of Into trait for component properties by @ModProg in #932
feat: add allow missing_docs to children field by @ModProg in #934
Adds the GetCbor and GetJson to server macro documentation. by @dgsantana in #938
Fix ServerFnError::Serialization error string by @mtsr in #939
examples: better practice for view types in todos by @gbj in #940
CI: fix unused variables breaking tests by @gbj in #950
fix: generics on impl From slot to Vec<slot> by @yuuma03 in #946
feat: add Actix extract helper by @gbj in #936
Test business logic for counter_without_macros by @agilarity in #927
impl IntoView for component props by @jquesada2016 in #948
impl FromIterator for View by @ModProg in #945
Add From for RequestParts into Parts for Axum and add an option to ge… by @benwis in #931
fix: <ErrorBoundary/> toggling between states (closes issue #820) by @gbj in #957
docs: add note on projecting children by @gbj in #959
fix: escapes in doc comments on component properties by @ModProg in #958
Add wasm web test and common tasks by @agilarity in #954
docs: note need for serde dependency for server functions (closes #947) by @gbj in #962
fix: use a HashMap on Branches::initialize by @yuuma03 in #966
chore: fix typos by @fattenap in #964
feat: add collect_view(cx) by @ModProg in #956
v0.3.0-alpha by @gbj in #968
Replace serde_urlencoded with serde_html_form to support cross-input vec serverfn by @snapbug in #973
change/fix: require FromStr errors on Params to be Send + Sync so they are ErrorBoundary compatible by @gbj in #974
Fix the lint issues in the counter example by @agilarity in #971
feat: add builder syntax for optional event listener by @gbj in #969
Fix lint issues in counter_isomorphic example by @agilarity in #980
fix: suppress warning loading local resource without <Suspense/> in hydrate mode (closes #979) by @gbj in #984
feat: allow structs in server function arguments by @gbj in #987
docs: switch from compile errors to runtime warnings for incompatible feature flags by @gbj in #990
docs: error when component ends with view! { ... }; (closes #985) by @gbj in #993
fix: lint issues in counters example by @agilarity in #986
fix: lint issues in erros_axum example by @agilarity in #988
fix: lint issues in fetch example by @agilarity in #989
fix: lint issues in hackernews example by @agilarity in #991
fix: lint issues in hackernews_axum example by @agilarity in #992
fix: lint issues in login_with_token_csr_only example by @agilarity in #995
fix: lint issues in router example by @agilarity in #996
fix: lint issues in session_auth_axum example by @agilarity in #997
fix: lint issues in todo_app_sqlite example by @agilarity in #998
fix: lint issues in todo_app_sqlite_axum example by @agilarity in #999
fix: lint issues in todo_app_sqlite_viz example by @agilarity in #1000
fix: lint issues in todomvc example by @agilarity in #1001
[docs] Reduce firmness of overlapping signal warning by @dglsparsons in #1004
docs: document that <ActionForm/> only works with form-encoded server functions by @gbj in #1005
fix: properly dispose of <Suspense/> scopes (closes #834) by @gbj in #1006
test: lint examples with --all-features by @agilarity in #1008
feat: add style: to view by @gbj in #1009
Relax Debug trait bounds by @Wadu436 in #1010
docs: add a server fn section by @gbj in #1014
book: close iframe tag on global state management page by @Wadu436 in #1013
docs: adjust Dynamic Attributes page by @FrankReh in #1011
book: fix link to cargo-leptos README by @Wadu436 in #1012
docs: add examples for manual server integration by @ChristopherPerry6060 in #1015
Clean up examples after verification by @agilarity in #1019
build tailwind CSS with trunk by @agilarity in #1016
[fix] indentation erros in examples by @hoangph271 in #1017
fix: maintain insertion order of meta tags by @gbj in #1021
fix: corrects error-deserialization behavior of ActionForm (closes #1024) by @gbj in #1025
feat: SsrMode::PartiallyBlocked by @gbj in #1026
fix: flicking <Transition/> in release mode (closes #960) by @gbj in #1030
fix: avoid extra { escaping (closes #1035) by @gbj in #1038
change: remove APIs that had been marked deprecated by @gbj in #1037
Update slice.rs by @sjud in #1036
examples: fix trunk config to run tailwind at the right time by @flosse in #1040
Migrate axum integration to use with_state over layer(Extension by @snapbug in #1032

New Contributors

@valeth made their first contribution in #787
@markcatley made their first contribution in #794
@Ofenhed made their first contribution in #799
@novacrazy made their first contribution in #805
@bram209 made their first contribution in #817
@akarras made their first contribution in #815
@hoangph271 made their first contribution in #840
@chroth7 made their first contribution in #860
@agilarity made their first contribution in #863
@Stackingttv made their first contribution in #869
@mustafasegf made their first contribution in #872
@kamilogorek made their first contribution in #876
@hjin-me made their first contribution in #879
@filipdutescu made their first contribution in #894
@OvermindDL1 made their first contribution in #891
@dgsantana made their first contribution in #895
@loganbnielsen made their first contribution in #910
@yuuma03 made their first contribution in #909
@escwxyz made their first contribution in #921
@rodrigc made their first contribution in #929
@bluenote10 made their first contribution in #925
@mtsr made their first contribution in #939
@fattenap made their first contribution in #964
@Wadu436 made their first contribution in #1010
@FrankReh made their first contribution in #1011
@ChristopherPerry6060 made their first contribution in #1015
@sjud made their first contribution in #1036

Full Changelog: v0.2.5...v0.3.0

leptos 0.3.0 `v0.3.0` on Rust Cargo