Don't apply semicolon in expressions from macros yet

std_detect is still using this and as it's in a submodule updating it will be a
pain. We can catch this either after a stdarch submodule bump or just on the
next cycle.

src/bootstrap/bootstrap.py

@@ -877,7 +877,8 @@ def build_bootstrap(self):
         target_linker = self.get_toml("linker", build_section)
         if target_linker is not None:
             env["RUSTFLAGS"] += " -C linker=" + target_linker
-        env["RUSTFLAGS"] += " -Wrust_2018_idioms -Wunused_lifetimes -Wsemicolon_in_expressions_from_macros"
+        # cfg(bootstrap): Add `-Wsemicolon_in_expressions_from_macros` after the next beta bump
+        env["RUSTFLAGS"] += " -Wrust_2018_idioms -Wunused_lifetimes"
         if self.get_toml("deny-warnings", "rust") != "false":
             env["RUSTFLAGS"] += " -Dwarnings"
 

src/bootstrap/builder.rs

@@ -1279,7 +1279,12 @@ impl<'a> Builder<'a> {
             // some code doesn't go through this `rustc` wrapper.
             lint_flags.push("-Wrust_2018_idioms");
             lint_flags.push("-Wunused_lifetimes");
-            lint_flags.push("-Wsemicolon_in_expressions_from_macros");
+            // cfg(bootstrap): unconditionally enable this warning after the next beta bump
+            // This is currently disabled for the stage1 libstd, since build scripts
+            // will end up using the bootstrap compiler (which doesn't yet support this lint)
+            if compiler.stage != 0 && mode != Mode::Std {
+                lint_flags.push("-Wsemicolon_in_expressions_from_macros");
+            }
 
             if self.config.deny_warnings {
                 lint_flags.push("-Dwarnings");