Add proc-macro2-fallback crate containing just the fallback implementation

Author: dtolnay

Cargo.toml

@@ -42,7 +42,7 @@ nightly = []
 doc-scrape-examples = false
 
 [workspace]
-members = ["benches/bench-libproc-macro", "tests/ui"]
+members = ["benches/bench-libproc-macro", "fallback", "tests/ui"]
 
 [patch.crates-io]
 # Our doc tests depend on quote which depends on proc-macro2. Without this line,

fallback/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "proc-macro2-fallback"
+version = "1.0.66"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+edition = "2021"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/dtolnay/proc-macro2"
+
+[lib]
+path = "../src/lib.rs"
+doc-scrape-examples = false
+
+[package.metadata.docs.rs]
+rustdoc-args = ["--cfg", "doc_cfg", "--generate-link-to-definition"]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+unicode-ident = "1"
+
+[dev-dependencies]
+proc-macro2 = { version = "1", path = "..", default_features = false }
+quote = { version = "1", default_features = false }