fix: Ensure exact token match in NameResolver (#14)

Previously we would use *any* preceding token from the SourceMap, and
may end up outputting `Foo.Foo.bar` for `Foo.prototype.bar` when the `prototype` token itself does not appear precisely in the SourceMap.

Author: Swatinem

src/name_resolver.rs

@@ -32,6 +32,12 @@ impl<'a, T: AsRef<str>> NameResolver<'a, T> {
         let token = self
             .sourcemap
             .lookup_token(source_position.line, source_position.column)?;
-        token.get_name()
+        let is_exact_match = token.get_dst() == (source_position.line, source_position.column);
+
+        if is_exact_match {
+            token.get_name()
+        } else {
+            None
+        }
     }
 }

tests/fixtures/README.md

@@ -1,3 +1,11 @@
+# Minifying code and creating SourceMaps:
+
+For example:
+
+```
+./node_modules/.bin/terser -c -m --module tests/fixtures/simple/original.js --source-map includeSources -o tests/fixtures/simple/minified.js
+```
+
 # trace
 
 A sync and async stack trace through various constructs, with named and anonymous

tests/fixtures/prototype-chain/README.md

@@ -0,0 +1,5 @@
+The SourceMap was hand-edited to remove the `prototype` token:
+
+The `EAAIC,UAAUC` portion in the middle of the mappings was replaced by `YAAcC`,
+as well as the `IAAKF,GAAKE` portion at the end was replaced by `IAAKD,GAAKC`,
+and the `"prototype"` was removed from `names`.

tests/fixtures/prototype-chain/minified.js

@@ -0,0 +1 @@
+function t(){}t.prototype.bar=()=>{};export default(new t).bar();

tests/fixtures/prototype-chain/minified.js.map

@@ -0,0 +1,3 @@
+function Foo() {}
+Foo.prototype.bar = () => {};
+export default (new Foo).bar();

tests/fixtures/prototype-chain/original.js

@@ -5,6 +5,10 @@ use js_source_scopes::{
     SourcePosition,
 };
 
+fn fixture(name: &str) -> String {
+    std::fs::read_to_string(format!("tests/fixtures/{name}")).unwrap()
+}
+
 fn resolve_original_scopes(
     minified: &str,
     map: &str,
@@ -199,3 +203,18 @@ fn parses_large_vendors() {
         println!("  original: {original:?}");
     }
 }
+
+#[test]
+fn should_only_resolve_exact() {
+    let minified = fixture("prototype-chain/minified.js");
+    let map = fixture("prototype-chain/minified.js.map");
+
+    let scopes = extract_scope_names(&minified).unwrap();
+
+    // The sourcemap was manually edited to remove the `prototype` token/name.
+    // When resolving names, we should make sure we have exact matches, otherwise
+    // we would use the preceding token and end up with `Foo.Foo.bar`.
+    let resolved_scopes = resolve_original_scopes(&minified, &map, scopes);
+
+    assert_eq!(resolved_scopes[1].2, Some("Foo.prototype.bar".into()));
+}