don't resolve main in lib crates

compiler/rustc_resolve/src/lib.rs

@@ -73,6 +73,7 @@
     ResolverGlobalCtxt, TyCtxt, TyCtxtFeed, Visibility,
 };
 use rustc_query_system::ich::StableHashingContext;
+use rustc_session::config::CrateType;
 use rustc_session::lint::builtin::PRIVATE_MACRO_USE;
 use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind, SyntaxContext, Transparency};
 use rustc_span::{DUMMY_SP, Ident, Macros20NormalizedIdent, Span, Symbol, kw, sym};
@@ -2430,6 +2431,12 @@ fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>> {
     }
 
     fn resolve_main(&mut self) {
+        let any_exe = self.tcx.crate_types().contains(&CrateType::Executable);
+        // Don't try to resolve main unless it's an executable
+        if !any_exe {
+            return;
+        }
+
         let module = self.graph_root;
         let ident = Ident::with_dummy_span(sym::main);
         let parent_scope = &ParentScope::module(module, self.arenas);

tests/ui/entry-point/imported_main_conflict_lib.rs

@@ -0,0 +1,10 @@
+// Tests that ambiguously glob importing main doesn't fail to compile in non-executable crates
+// Regression test for #149412
+//@ check-pass
+#![crate_type = "lib"]
+
+mod m1 { pub(crate) fn main() {} }
+mod m2 { pub(crate) fn main() {} }
+
+use m1::*;
+use m2::*;