Make build output deterministic by remapping paths

[ldk-c-bindings] / deterministic-build-wrappers / rustc

diff --git a/deterministic-build-wrappers/rustc b/deterministic-build-wrappers/rustc
new file mode 100755 (executable)
index 0000000..2f35677
--- /dev/null
+++ b/deterministic-build-wrappers/rustc
@@ -0,0 +1,30 @@
+#!/bin/bash
+# rustc calculates a unique metadata tag to mangle symbols which includes the
+# actual path to the crate. This breaks our deterministic builds as we depend
+# on a copy of rust-lightning via a path. We insert this shim between cargo and
+# rustc and edit the metadata tag for rust-lightning.
+# While we could just set RUSTFLAGS="-C metadata=42", this would break if we
+# ever (indirectly) depend on multiple versions of the same crate.
+args=("$@")
+IS_LIGHTNING=false
+for ((i=0; i<"${#args[@]}"; ++i)); do
+    case ${args[i]} in
+        --crate-name)
+                       if [ "${args[i+1]}" = "lightning" ]; then
+                               IS_LIGHTNING=true
+                       fi
+                       ;;
+    esac
+done
+for ((i=0; i<"${#args[@]}"; ++i)); do
+    case ${args[i]} in
+        metadata*)
+                       if [ "$IS_LIGHTNING" = "true" ]; then
+                               # Pick any random value for metadata, it doesn't matter
+                               args[i]="metadata=42"
+                       fi
+                       ;;
+    esac
+done
+
+/usr/bin/rustc "${args[@]}"