Bug 1335203 - Synchronize rust debug-assertions with C++ DEBUG, r=froydnj

MozReview-Commit-ID: JPD9eNFg89S

config/rules.mk

@@ -940,7 +940,13 @@ endif
 # optimization level here, if necessary.  (The Cargo.toml files already
 # specify debug-assertions appropriately for --{disable,enable}-debug.)
 ifndef MOZ_OPTIMIZE
-rustflags_override = RUSTFLAGS='-C opt-level=0'
+rustflags = -C opt-level=0
+# Unfortunately, -C opt-level=0 implies -C debug-assertions, so we need
+# to explicitly disable them when MOZ_DEBUG is not set.
+ifndef MOZ_DEBUG
+rustflags += -C debug-assertions=no
+endif
+rustflags_override = RUSTFLAGS='$(rustflags)'
 endif
 
 CARGO_BUILD = env $(rustflags_override) \

xpcom/string/nsSubstring.cpp

@@ -355,12 +355,14 @@ static_assert(sizeof(nsStringContainer_base) == sizeof(nsSubstring),
 // Provide rust bindings to the nsA[C]String types
 extern "C" {
 
-// This is a no-op on release, when bug 1335203 is fixed we should ifdef this
-// to ensure using it in release results in a linker error.
+// This is a no-op on release, so we ifdef it out such that using it in release
+// results in a linker error.
+#ifdef DEBUG
 void Gecko_IncrementStringAdoptCount(void* aData)
 {
   MOZ_LOG_CTOR(aData, "StringAdopt", 1);
 }
+#endif
 
 void Gecko_FinalizeCString(nsACString* aThis)
 {