Check for escape sequences in Fluent resources

tests/ui-fulldeps/fluent-messages/invalid-escape.ftl

@@ -0,0 +1 @@
+no_crate_bad_escape = don't use \n, \', or \"

tests/ui-fulldeps/fluent-messages/test.rs

@@ -92,3 +92,12 @@ mod missing_message_ref {
     fluent_messages! { "./missing-message-ref.ftl" }
     //~^ ERROR referenced message `message` does not exist
 }
+
+mod bad_escape {
+    use super::fluent_messages;
+
+    fluent_messages! { "./invalid-escape.ftl" }
+    //~^ ERROR invalid escape `\n`
+    //~| ERROR invalid escape `\"`
+    //~| ERROR invalid escape `\'`
+}

tests/ui-fulldeps/fluent-messages/test.stderr

@@ -83,5 +83,29 @@ LL |     fluent_messages! { "./missing-message-ref.ftl" }
    |
    = help: you may have meant to use a variable reference (`{$message}`)
 
-error: aborting due to 10 previous errors
+error: invalid escape `\n` in Fluent resource
+  --> $DIR/test.rs:99:24
+   |
+LL |     fluent_messages! { "./invalid-escape.ftl" }
+   |                        ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: os-specific message
+
+error: invalid escape `\"` in Fluent resource
+  --> $DIR/test.rs:99:24
+   |
+LL |     fluent_messages! { "./invalid-escape.ftl" }
+   |                        ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: os-specific message
+
+error: invalid escape `\'` in Fluent resource
+  --> $DIR/test.rs:99:24
+   |
+LL |     fluent_messages! { "./invalid-escape.ftl" }
+   |                        ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: os-specific message
+
+error: aborting due to 13 previous errors
 

tests/ui-fulldeps/internal-lints/existing_doc_keyword.stderr

@@ -1,4 +1,4 @@
-error: found non-existing keyword `tadam` used in `#[doc(keyword = \"...\")]`
+error: found non-existing keyword `tadam` used in `#[doc(keyword = "...")]`
   --> $DIR/existing_doc_keyword.rs:10:1
    |
 LL | #[doc(keyword = "tadam")]