Suggest valid command-line crate names

compiler/rustc_session/src/diagnostics.rs

@@ -435,11 +435,20 @@ pub(crate) struct CrateNameEmpty {
 
 #[derive(Diagnostic)]
 #[diag("invalid character {$character} in crate name: `{$crate_name}`")]
+#[note("crate names may only contain alphanumeric characters or underscores")]
 pub(crate) struct InvalidCharacterInCrateName {
     #[primary_span]
     pub(crate) span: Option<Span>,
     pub(crate) character: char,
     pub(crate) crate_name: Symbol,
+    #[subdiagnostic]
+    pub(crate) suggestion: Option<InvalidCharacterInCrateNameSuggestion>,
+}
+
+#[derive(Subdiagnostic)]
+#[help("you might have meant to use `--crate-name={$suggested_name}`")]
+pub(crate) struct InvalidCharacterInCrateNameSuggestion {
+    pub(crate) suggested_name: String,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_session/src/output.rs

@@ -6,7 +6,10 @@ use rustc_span::{Span, Symbol};
 
 use crate::Session;
 use crate::config::{CrateType, OutFileName, OutputFilenames, OutputType};
-use crate::diagnostics::{CrateNameEmpty, FileIsNotWriteable, InvalidCharacterInCrateName};
+use crate::diagnostics::{
+    CrateNameEmpty, FileIsNotWriteable, InvalidCharacterInCrateName,
+    InvalidCharacterInCrateNameSuggestion,
+};
 
 pub fn out_filename(
     sess: &Session,
@@ -68,6 +71,10 @@ pub fn validate_crate_name(sess: &Session, crate_name: Symbol, span: Option<Span
             span,
             character: c,
             crate_name,
+            suggestion: span.is_none().then(|| InvalidCharacterInCrateNameSuggestion {
+                suggested_name:
+                    crate_name.as_str().replace(|c: char| c != '_' && !c.is_alphanumeric(), "_"),
+            }),
         }));
     }
 

tests/ui/compile-flags/invalid/invalid-crate-name-suggestion-issue-159485.rs

@@ -0,0 +1,7 @@
+// Invalid command-line crate names should suggest a sanitized replacement.
+
+//@ compile-flags: --crate-name=my-crate
+
+fn main() {}
+
+//~? ERROR invalid character '-' in crate name

tests/ui/compile-flags/invalid/invalid-crate-name-suggestion-issue-159485.stderr

@@ -0,0 +1,7 @@
+error: invalid character '-' in crate name: `my-crate`
+   |
+   = note: crate names may only contain alphanumeric characters or underscores
+   = help: you might have meant to use `--crate-name=my_crate`
+
+error: aborting due to 1 previous error
+

tests/ui/compile-flags/invalid/need-crate-arg-ignore-tidy$x.stderr

@@ -1,4 +1,7 @@
 error: invalid character '$' in crate name: `need_crate_arg_ignore_tidy$x`
+   |
+   = note: crate names may only contain alphanumeric characters or underscores
+   = help: you might have meant to use `--crate-name=need_crate_arg_ignore_tidy_x`
 
 error: aborting due to 1 previous error