Current sp-core crate (version 7.0.0) with feature full_crypto depends on libsecp256k1 crate with version = "0.7", default-features = false, features = ["static-context"].
full_crypto is a feature intended for no_std support and libsecp256k1 with default-features = false is supposed to work with no_std. However, libsecp256k1 with default-features = false currently does not compile at least on targets thumbv7m-none-eabi and thumbv7em-none-eabi causing sp-core in full_crypto to not compile as well.
Possible fix
[build-dependencies] contain libsecp256k1-gen-ecmult and libsecp256k1-gen-genmult, both depending on libsecp256k1-core with default features (i.e. in std mode).
If the Cargo.toml files for both libsecp256k1-gen-ecmult and libsecp256k1-gen-genmult are changed to have libsecp256k1-core with default-features = false, things keep building as before in std and begin to build in no-std as well.
Also, a few dependencies (serde and base64) get used only in std, but were not marked as optional = true, although this does not affect buildability.
We will maintain a thus fixed version of the crate for Kampela development and switch to this upstream if the issue gets resolved.
Problem
Current
sp-corecrate (version7.0.0) with featurefull_cryptodepends onlibsecp256k1crate withversion = "0.7", default-features = false, features = ["static-context"].full_cryptois a feature intended forno_stdsupport andlibsecp256k1withdefault-features = falseis supposed to work withno_std. However,libsecp256k1withdefault-features = falsecurrently does not compile at least on targetsthumbv7m-none-eabiandthumbv7em-none-eabicausingsp-coreinfull_cryptoto not compile as well.Possible fix
[build-dependencies]containlibsecp256k1-gen-ecmultandlibsecp256k1-gen-genmult, both depending onlibsecp256k1-corewith default features (i.e. instdmode). If theCargo.tomlfiles for bothlibsecp256k1-gen-ecmultandlibsecp256k1-gen-genmultare changed to havelibsecp256k1-corewithdefault-features = false, things keep building as before instdand begin to build inno-stdas well. Also, a few dependencies (serdeandbase64) get used only instd, but were not marked asoptional = true, although this does not affect buildability.We will maintain a thus fixed version of the crate for Kampela development and switch to this upstream if the issue gets resolved.