Fallback to spec shaking v1 if env var is not set

Makefile

@@ -30,9 +30,21 @@ build: build-libs build-test-wasms
 build-libs: fmt
 	cargo hack build --release $(foreach c,$(LIB_CRATES),--package $(c))
 
+# First, build crate used as WASM deps to other test crates.
+# Then, build `test_spec_shaking_v2` without the spec shaking v2 env var to verify
+# that it falls back to spec_shaking_v1 behaviour.
+# Then, build the test wasms with MSRV by default, with some meta disabled for
+# binary stability for tests.
 build-test-wasms: fmt
-	# Build the test wasms with MSRV by default, with some meta disabled for
-	# binary stability for tests.
+	SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2=1 \
+	RUSTUP_TOOLCHAIN=$(TEST_CRATES_RUSTUP_TOOLCHAIN) \
+	RUSTFLAGS='--cfg soroban_sdk_internal_no_rssdkver_meta' \
+		cargo build --release --target wasm32v1-none --package test_spec_import
+	RUSTUP_TOOLCHAIN=$(TEST_CRATES_RUSTUP_TOOLCHAIN) \
+	RUSTFLAGS='--cfg soroban_sdk_internal_no_rssdkver_meta' \
+		cargo build --release --target wasm32v1-none --package test_spec_shaking_v2
+	cp target/wasm32v1-none/release/test_spec_shaking_v2.wasm \
+		target/wasm32v1-none/release/test_spec_shaking_v2_no_env.wasm
 	SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2=1 \
 	RUSTUP_TOOLCHAIN=$(TEST_CRATES_RUSTUP_TOOLCHAIN) \
 	RUSTFLAGS='--cfg soroban_sdk_internal_no_rssdkver_meta' \

soroban-sdk-macros/src/derive_enum.rs

@@ -9,7 +9,10 @@ use stellar_xdr::{
     ScSpecUdtUnionCaseVoidV0, ScSpecUdtUnionV0, StringM, VecM, WriteXdr, SCSYMBOL_LIMIT,
 };
 
-use crate::{doc::docs_from_attrs, map_type::map_type, shaking, DEFAULT_XDR_RW_LIMITS};
+use crate::{
+    doc::docs_from_attrs, map_type::map_type, shaking, spec_shaking_v2_enabled,
+    DEFAULT_XDR_RW_LIMITS,
+};
 
 pub fn derive_type_enum(
     path: &Path,
@@ -175,9 +178,9 @@ pub fn derive_type_enum(
         None
     };
 
-    // SpecShakingMarker impl - only generated when spec is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when spec is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if spec_shaking_v2_enabled() {
         spec_xdr.as_ref().map(|spec_xdr| {
             // Flatten all variant field types for shaking calls, deduplicating
             // to avoid redundant calls for types that appear in multiple variants.

soroban-sdk-macros/src/derive_enum_int.rs

@@ -7,7 +7,7 @@ use syn::{spanned::Spanned, Attribute, DataEnum, Error, ExprLit, Ident, Lit, Pat
 
 use stellar_xdr::{ScSpecEntry, ScSpecUdtEnumCaseV0, WriteXdr};
 
-use crate::{doc::docs_from_attrs, shaking, DEFAULT_XDR_RW_LIMITS};
+use crate::{doc::docs_from_attrs, shaking, spec_shaking_v2_enabled, DEFAULT_XDR_RW_LIMITS};
 
 // TODO: Add conversions to/from ScVal types.
 
@@ -97,9 +97,9 @@ pub fn derive_type_enum_int(
         None
     };
 
-    // SpecShakingMarker impl - only generated when spec is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when spec is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if spec_shaking_v2_enabled() {
         spec_xdr.as_ref().map(|spec_xdr| {
             shaking::generate_marker_impl(
                 path,

soroban-sdk-macros/src/derive_error_enum_int.rs

@@ -5,7 +5,7 @@ use stellar_xdr::curr as stellar_xdr;
 use stellar_xdr::{ScSpecEntry, ScSpecUdtErrorEnumCaseV0, ScSpecUdtErrorEnumV0, StringM, WriteXdr};
 use syn::{spanned::Spanned, Attribute, DataEnum, Error, ExprLit, Ident, Lit, Path};
 
-use crate::{doc::docs_from_attrs, shaking, DEFAULT_XDR_RW_LIMITS};
+use crate::{doc::docs_from_attrs, shaking, spec_shaking_v2_enabled, DEFAULT_XDR_RW_LIMITS};
 
 pub fn derive_type_error_enum_int(
     path: &Path,
@@ -95,9 +95,9 @@ pub fn derive_type_error_enum_int(
         None
     };
 
-    // SpecShakingMarker impl - only generated when spec is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when spec is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if spec_shaking_v2_enabled() {
         spec_xdr.as_ref().map(|spec_xdr| {
             shaking::generate_marker_impl(
                 path,

soroban-sdk-macros/src/derive_event.rs

@@ -1,6 +1,6 @@
 use crate::{
     attribute::remove_attributes_from_item, default_crate_path, doc::docs_from_attrs,
-    map_type::map_type, shaking, symbol, DEFAULT_XDR_RW_LIMITS,
+    map_type::map_type, shaking, spec_shaking_v2_enabled, symbol, DEFAULT_XDR_RW_LIMITS,
 };
 use darling::{ast::NestedMeta, Error, FromMeta};
 use heck::ToSnakeCase;
@@ -197,7 +197,7 @@ fn derive_impls(args: &ContractEventArgs, input: &DeriveInput) -> Result<TokenSt
         "__SPEC_XDR_EVENT_{}",
         input.ident.to_string().to_uppercase()
     );
-    let spec_shaking_call = if export && cfg!(feature = "experimental_spec_shaking_v2") {
+    let spec_shaking_call = if export && spec_shaking_v2_enabled() {
         Some(quote! { <Self as #path::SpecShakingMarker>::spec_shaking_marker(); })
     } else {
         None
@@ -215,9 +215,9 @@ fn derive_impls(args: &ContractEventArgs, input: &DeriveInput) -> Result<TokenSt
         }
     };
 
-    // SpecShakingMarker impl - only generated when export is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if export && cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when export is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if export && spec_shaking_v2_enabled() {
         Some(shaking::generate_marker_impl(
             path,
             quote!(#ident),

soroban-sdk-macros/src/derive_struct.rs

@@ -8,7 +8,10 @@ use stellar_xdr::{
     ScSpecEntry, ScSpecTypeDef, ScSpecUdtStructFieldV0, ScSpecUdtStructV0, StringM, WriteXdr,
 };
 
-use crate::{doc::docs_from_attrs, map_type::map_type, shaking, DEFAULT_XDR_RW_LIMITS};
+use crate::{
+    doc::docs_from_attrs, map_type::map_type, shaking, spec_shaking_v2_enabled,
+    DEFAULT_XDR_RW_LIMITS,
+};
 
 // TODO: Add field attribute for including/excluding fields in types.
 // TODO: Better handling of partial types and types without all their fields and
@@ -107,9 +110,9 @@ pub fn derive_type_struct(
         None
     };
 
-    // SpecShakingMarker impl - only generated when spec is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when spec is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if spec_shaking_v2_enabled() {
         spec_xdr.as_ref().map(|spec_xdr| {
             shaking::generate_marker_impl(
                 path,

soroban-sdk-macros/src/derive_struct_tuple.rs

@@ -8,7 +8,10 @@ use stellar_xdr::{
     ScSpecEntry, ScSpecTypeDef, ScSpecUdtStructFieldV0, ScSpecUdtStructV0, StringM, WriteXdr,
 };
 
-use crate::{doc::docs_from_attrs, map_type::map_type, shaking, DEFAULT_XDR_RW_LIMITS};
+use crate::{
+    doc::docs_from_attrs, map_type::map_type, shaking, spec_shaking_v2_enabled,
+    DEFAULT_XDR_RW_LIMITS,
+};
 
 pub fn derive_type_struct_tuple(
     path: &Path,
@@ -96,9 +99,9 @@ pub fn derive_type_struct_tuple(
         None
     };
 
-    // SpecShakingMarker impl - only generated when spec is true and the
-    // experimental_spec_shaking_v2 feature is enabled.
-    let spec_shaking_impl = if cfg!(feature = "experimental_spec_shaking_v2") {
+    // SpecShakingMarker impl - only generated when spec is true and
+    // spec shaking v2 is enabled.
+    let spec_shaking_impl = if spec_shaking_v2_enabled() {
         spec_xdr.as_ref().map(|spec_xdr| {
             shaking::generate_marker_impl(
                 path,

soroban-sdk-macros/src/lib.rs

@@ -80,6 +80,15 @@ pub(crate) fn default_crate_path() -> Path {
     parse_str("soroban_sdk").unwrap()
 }
 
+/// Returns true if spec shaking v2 should be used. Requires both the
+/// `experimental_spec_shaking_v2` feature to be enabled on the macro crate AND
+/// the `SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2` env var to be set
+/// at the time the macro expands (i.e. when the consumer crate is compiled).
+fn spec_shaking_v2_enabled() -> bool {
+    cfg!(feature = "experimental_spec_shaking_v2")
+        && std::env::var("SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2").is_ok()
+}
+
 #[derive(Debug, FromMeta)]
 struct ContractSpecArgs {
     name: Type,
@@ -428,10 +437,10 @@ pub fn contracttype(metadata: TokenStream, input: TokenStream) -> TokenStream {
     }
     // If the export argument has a value, do as it instructs regarding
     // exporting. If it does not have a value, export if the type is pub,
-    // or always export when spec shaking is enabled.
+    // or always export when spec shaking v2 is enabled.
     let gen_spec = if let Some(export) = args.export {
         export
-    } else if cfg!(feature = "experimental_spec_shaking_v2") {
+    } else if spec_shaking_v2_enabled() {
         true
     } else {
         matches!(input.vis, Visibility::Public(_))
@@ -502,10 +511,10 @@ pub fn contracterror(metadata: TokenStream, input: TokenStream) -> TokenStream {
     let attrs = &input.attrs;
     // If the export argument has a value, do as it instructs regarding
     // exporting. If it does not have a value, export if the type is pub,
-    // or always export when spec shaking is enabled.
+    // or always export when spec shaking v2 is enabled.
     let gen_spec = if let Some(export) = args.export {
         export
-    } else if cfg!(feature = "experimental_spec_shaking_v2") {
+    } else if spec_shaking_v2_enabled() {
         true
     } else {
         matches!(input.vis, Visibility::Public(_))
@@ -691,10 +700,9 @@ pub fn contractimport(metadata: TokenStream) -> TokenStream {
         }
     };
 
-    // Generate with options based on whether the experimental_spec_shaking_v2
-    // feature is enabled.
+    // Generate with options based on whether spec shaking v2 is enabled
     let opts = GenerateOptions {
-        export: cfg!(feature = "experimental_spec_shaking_v2"),
+        export: spec_shaking_v2_enabled(),
     };
     match generate_from_wasm_with_options(&wasm, &args.file, args.sha256.as_deref(), &opts) {
         Ok(code) => quote! { #code },

soroban-sdk/build.rs

@@ -21,25 +21,23 @@ pub fn main() {
     }
 
     // When the experimental_spec_shaking_v2 feature is enabled, check for an env var from the
-    // build system (Stellar CLI) that indicates it supports spec optimization using markers.
+    // build system (like Stellar CLI) that indicates it supports spec optimization using markers.
+    // If the env var is set, enable spec_shaking_v2 cfg for the crate. If not, fall back to
+    // spec shaking v1 behavior and emit a warning on wasm targets.
+    println!("cargo::rustc-check-cfg=cfg(spec_shaking_v2)");
     if std::env::var("CARGO_FEATURE_EXPERIMENTAL_SPEC_SHAKING_V2").is_ok() {
         let env_name = "SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2";
         println!("cargo::rerun-if-env-changed={env_name}");
-        if std::env::var(env_name).is_err()
-            && std::env::var("CARGO_CFG_TARGET_FAMILY").unwrap_or_default() == "wasm"
-        {
-            panic!(
-                "\
-\n\nerror: soroban-sdk feature 'experimental_spec_shaking_v2' requires stellar-cli v25.2.0+\
-\n\
-\nThe soroban-sdk 'experimental_spec_shaking_v2' feature requires building\
-\nwith `stellar contract build` from stellar-cli v25.2.0 or newer.\
-\n\
-\nTo fix, either:\
-\n  - Build with `stellar contract build` using stellar-cli v25.2.0+\
-\n  - Disable the feature by removing 'experimental_spec_shaking_v2' from\
-\n    the soroban-sdk import features list in Cargo.toml.\
-\n"
+        if std::env::var(env_name).is_ok() {
+            println!("cargo::rustc-cfg=spec_shaking_v2");
+        } else if std::env::var("CARGO_CFG_TARGET_FAMILY").unwrap_or_default() == "wasm" {
+            println!(
+                "cargo::warning=soroban-sdk: feature 'experimental_spec_shaking_v2' was enabled but not used, \
+                 because this build was not started by a tool that supports spec shaking v2. \
+                 Falling back to spec shaking v1. To use v2, use a build tool that supports \
+                 spec shaking v2 such as stellar-cli v25.2.0+ with `stellar contract build`. \
+                 To manually use v2 without a supporting build tool, set the env var \
+                 SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2 before building."
             );
         }
     }

soroban-sdk/src/_features.rs

@@ -135,11 +135,16 @@
 //!
 //! ### Build Requirements
 //!
-//! This feature requires building with `stellar contract build` from
-//! `stellar-cli` v25.2.0 or newer. Building directly with `cargo build` will
-//! produce a build error unless the
-//! `SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2` environment variable is
-//! set.
+//! Spec shaking v2 requires the
+//! `SOROBAN_SDK_BUILD_SYSTEM_SUPPORTS_SPEC_SHAKING_V2` environment variable to
+//! be set at build time. This is automatically set by `stellar contract build`
+//! from `stellar-cli` v25.2.0 or newer.
+//!
+//! When the `experimental_spec_shaking_v2` feature is enabled but the env var
+//! is not set, the SDK falls back to spec shaking v1 behavior and emits a
+//! compiler warning on wasm targets. This allows contracts to build with plain
+//! `cargo build` without errors, while still benefiting from v2 when built
+//! with compatible tooling.
 //!
 //! [`contracttype`]: crate::contracttype
 //! [`contracterror`]: crate::contracterror

soroban-sdk/src/into_val_for_contract_fn.rs

@@ -20,7 +20,7 @@ pub trait IntoValForContractFn {
     fn into_val_for_contract_fn(self, env: &Env) -> Val;
 }
 
-#[cfg(feature = "experimental_spec_shaking_v2")]
+#[cfg(spec_shaking_v2)]
 #[doc(hidden)]
 #[allow(deprecated)]
 impl<T> IntoValForContractFn for T
@@ -33,7 +33,7 @@ where
     }
 }
 
-#[cfg(not(feature = "experimental_spec_shaking_v2"))]
+#[cfg(not(spec_shaking_v2))]
 #[doc(hidden)]
 #[allow(deprecated)]
 impl<T> IntoValForContractFn for T

soroban-sdk/src/lib.rs

@@ -118,11 +118,11 @@ const _: () = {
         val = concat!(env!("CARGO_PKG_VERSION"), "#", env!("GIT_REVISION")),
     );
 
-    // An indicator of the spec shaking version in use. Signals to the stellar-cli that the .wasm
+    // An indicator of the spec shaking version in use. Signals to the post-build system that the .wasm
     // needs to have its spec shaken. See soroban_spec::shaking for constants and version detection.
     // The contractmeta! macro requires string literals, so we assert the literals match the
     // constants defined in soroban_spec::shaking.
-    #[cfg(feature = "experimental_spec_shaking_v2")]
+    #[cfg(spec_shaking_v2)]
     contractmeta!(key = "rssdk_spec_shaking", val = "2");
 };
 
@@ -1195,9 +1195,9 @@ mod into_val_for_contract_fn;
 #[allow(deprecated)]
 pub use into_val_for_contract_fn::IntoValForContractFn;
 
-#[cfg(feature = "experimental_spec_shaking_v2")]
+#[cfg(spec_shaking_v2)]
 mod spec_shaking;
-#[cfg(feature = "experimental_spec_shaking_v2")]
+#[cfg(spec_shaking_v2)]
 #[doc(hidden)]
 pub use spec_shaking::SpecShakingMarker;
 

soroban-sdk/src/try_from_val_for_contract_fn.rs

@@ -30,7 +30,7 @@ pub trait TryFromValForContractFn<E: Env, V: ?Sized>: Sized {
     fn try_from_val_for_contract_fn(env: &E, v: &V) -> Result<Self, Self::Error>;
 }
 
-#[cfg(feature = "experimental_spec_shaking_v2")]
+#[cfg(spec_shaking_v2)]
 #[doc(hidden)]
 #[allow(deprecated)]
 impl<E: Env, T, U> TryFromValForContractFn<E, T> for U
@@ -44,7 +44,7 @@ where
     }
 }
 
-#[cfg(not(feature = "experimental_spec_shaking_v2"))]
+#[cfg(not(spec_shaking_v2))]
 #[doc(hidden)]
 #[allow(deprecated)]
 impl<E: Env, T, U> TryFromValForContractFn<E, T> for U

tests-expanded/test_account_tests.rs

@@ -56,11 +56,6 @@ impl Error {
         *b"\0\0\0\x04\0\0\0\0\0\0\0\0\0\0\0\x05Error\0\0\0\0\0\0\x01\0\0\0\0\0\0\0\x04Fail\0\0\0\x01"
     }
 }
-impl soroban_sdk::SpecShakingMarker for Error {
-    #[doc(hidden)]
-    #[inline(always)]
-    fn spec_shaking_marker() {}
-}
 impl TryFrom<soroban_sdk::Error> for Error {
     type Error = soroban_sdk::Error;
     #[inline(always)]

tests-expanded/test_auth_tests.rs

@@ -1124,11 +1124,6 @@ mod test_a {
                 *b"\0\0\0\x04\0\0\0\0\0\0\0\0\0\0\0\x05Error\0\0\0\0\0\0\x01\0\0\0\0\0\0\0\x07Decline\0\0\0\0\x01"
             }
         }
-        impl soroban_sdk::SpecShakingMarker for Error {
-            #[doc(hidden)]
-            #[inline(always)]
-            fn spec_shaking_marker() {}
-        }
         impl TryFrom<soroban_sdk::Error> for Error {
             type Error = soroban_sdk::Error;
             #[inline(always)]
@@ -2606,11 +2601,6 @@ mod test_b {
                 *b"\0\0\0\x04\0\0\0\0\0\0\0\0\0\0\0\x05Error\0\0\0\0\0\0\x01\0\0\0\0\0\0\0\x07Decline\0\0\0\0\x01"
             }
         }
-        impl soroban_sdk::SpecShakingMarker for Error {
-            #[doc(hidden)]
-            #[inline(always)]
-            fn spec_shaking_marker() {}
-        }
         impl TryFrom<soroban_sdk::Error> for Error {
             type Error = soroban_sdk::Error;
             #[inline(always)]