Rust: Model to_string.

Author: geoffw0

rust/ql/lib/codeql/rust/frameworks/stdlib/lang-core.model.yml

@@ -31,3 +31,4 @@ extensions:
       # String
       - ["lang:alloc", "<crate::string::String>::as_str", "Argument[self]", "ReturnValue", "taint", "manual"]
       - ["lang:alloc", "<crate::string::String>::as_bytes", "Argument[self]", "ReturnValue", "taint", "manual"]
+      - ["lang:alloc", "<_ as crate::string::ToString>::to_string", "Argument[self]", "ReturnValue", "taint", "manual"]

rust/ql/test/library-tests/dataflow/local/main.rs

@@ -440,7 +440,7 @@ fn parse() {
     let d : i64 = b.parse().unwrap();
 
     sink(a); // $ hasValueFlow=90
-    sink_string(b); // $ MISSING: hasTaintFlow=90
+    sink_string(b); // $ hasTaintFlow=90
     sink(c); // $ MISSING: hasTaintFlow=90
     sink(d); // $ MISSING: hasTaintFlow=90
 }