Rollup merge of #22664 - lfairy:just-say-no, r=alexcrichton

 Leading hyphens already don't work (#22661), so no code should break from this change.

Closes #22661.

src/librustc/metadata/creader.rs

@@ -81,6 +81,8 @@ pub fn validate_crate_name(sess: Option<&Session>, s: &str, sp: Option<Span>) {
     };
     if s.len() == 0 {
         err("crate name must not be empty");
+    } else if s.char_at(0) == '-' {
+        err(&format!("crate name cannot start with a hyphen: {}", s));
     }
     for c in s.chars() {
         if c.is_alphanumeric() { continue }

src/test/run-make/weird-output-filenames/Makefile

@@ -10,3 +10,6 @@ all:
 	cp foo.rs $(TMPDIR)/+foo+bar
 	$(RUSTC) $(TMPDIR)/+foo+bar 2>&1 \
 		| grep "invalid character.*in crate name:"
+	cp foo.rs $(TMPDIR)/-foo.rs
+	$(RUSTC) $(TMPDIR)/-foo.rs 2>&1 \
+		| grep "crate name cannot start with a hyphen:"