restore dependency of pyo3-macros-backend on pyo3-build-config

Cargo.toml

@@ -81,7 +81,7 @@ multiple-pymethods = ["inventory", "pyo3-macros/multiple-pymethods"]
 extension-module = ["pyo3-ffi/extension-module"]
 
 # Use the Python limited API. See https://www.python.org/dev/peps/pep-0384/ for more.
-abi3 = ["pyo3-build-config/abi3", "pyo3-ffi/abi3", "pyo3-macros/abi3"]
+abi3 = ["pyo3-build-config/abi3", "pyo3-ffi/abi3"]
 
 # With abi3, we can manually set the minimum Python version.
 abi3-py37 = ["abi3-py38", "pyo3-build-config/abi3-py37", "pyo3-ffi/abi3-py37"]

pyo3-macros-backend/Cargo.toml

@@ -14,17 +14,15 @@ edition = "2021"
 # not to depend on proc-macro itself.
 # See https://github.com/PyO3/pyo3/pull/810 for more.
 [dependencies]
-quote = { version = "1", default-features = false }
-proc-macro2 = { version = "1", default-features = false }
 heck = "0.4"
+proc-macro2 = { version = "1", default-features = false }
+pyo3-build-config = { path = "../pyo3-build-config", version = "0.21.0-dev", features = ["resolve-config"] }
+quote = { version = "1", default-features = false }
 
 [dependencies.syn]
 version = "2"
 default-features = false
 features = ["derive", "parsing", "printing", "clone-impls", "full", "extra-traits"]
 
-[features]
-abi3 = []
-
 [lints]
 workspace = true

pyo3-macros-backend/src/utils.rs

@@ -168,7 +168,5 @@ pub fn apply_renaming_rule(rule: RenamingRule, name: &str) -> String {
 }
 
 pub(crate) fn is_abi3() -> bool {
-    cfg!(feature = "abi3")
-        || std::env::var_os("PYO3_USE_ABI3_FORWARD_COMPATIBILITY")
-            .map_or(false, |os_str| os_str == "1")
+    pyo3_build_config::get().abi3
 }

pyo3-macros/Cargo.toml

@@ -16,8 +16,6 @@ proc-macro = true
 [features]
 multiple-pymethods = []
 
-abi3 = ["pyo3-macros-backend/abi3"]
-
 [dependencies]
 proc-macro2 = { version = "1", default-features = false }
 quote = "1"