Fix last_files_match_only to evaluate per file instead of globally

src/reviewer.js

@@ -48,16 +48,28 @@ function identify_reviewers_by_changed_files({ config, changed_files, excludes =
     return [];
   }
 
-  const matching_reviewers = [];
-
-  Object.entries(config.files).forEach(([ glob_pattern, reviewers ]) => {
-    if (changed_files.some((changed_file) => minimatch(changed_file, glob_pattern))) {
-      if (last_files_match_only) {
-        matching_reviewers.length = 0; // clear previous matches
+  let matching_reviewers;
+
+  if (last_files_match_only) {
+    const file_patterns = Object.entries(config.files);
+    const per_file_reviewers = changed_files.flatMap((changed_file) => {
+      let last_matching_reviewers = null;
+      file_patterns.forEach(([ glob_pattern, reviewers ]) => {
+        if (minimatch(changed_file, glob_pattern)) {
+          last_matching_reviewers = reviewers;
+        }
+      });
+      return last_matching_reviewers || [];
+    });
+    matching_reviewers = per_file_reviewers;
+  } else {
+    matching_reviewers = [];
+    Object.entries(config.files).forEach(([ glob_pattern, reviewers ]) => {
+      if (changed_files.some((changed_file) => minimatch(changed_file, glob_pattern))) {
+        matching_reviewers.push(...reviewers);
       }
-      matching_reviewers.push(...reviewers);
-    }
-  });
+    });
+  }
 
   const individuals = replace_groups_with_individuals({ reviewers: matching_reviewers, config });
 

test/reviewer.test.js

@@ -126,6 +126,43 @@ describe('reviewer', function() {
       };
       expect(identify_reviewers_by_changed_files({ config: config_with_last_files_match_only, changed_files })).to.have.members([ 'mario', 'someone-specific' ]);
     });
+
+    context('with `last_files_match_only` and a specific file override with empty reviewers', function() {
+      const override_config = {
+        reviewers: {
+          groups: {
+            'team-a': [ 'alice', 'bob' ],
+          },
+        },
+        files: {
+          'src/**/*': [ 'team-a' ],
+          'src/generated-file.dat': [],
+        },
+        options: {
+          last_files_match_only: true,
+        },
+      };
+
+      it('returns reviewers when a file only matches the wildcard pattern', function() {
+        const changed_files = [ 'src/main-code.js' ];
+        expect(identify_reviewers_by_changed_files({ config: override_config, changed_files })).to.have.members([ 'alice', 'bob' ]);
+      });
+
+      it('returns no reviewers when a file only matches the overriding empty pattern', function() {
+        const changed_files = [ 'src/generated-file.dat' ];
+        expect(identify_reviewers_by_changed_files({ config: override_config, changed_files })).to.deep.equal([]);
+      });
+
+      it('returns no reviewers when all files are unmatched or overridden with empty reviewers', function() {
+        const changed_files = [ 'unrelated-file.txt', 'src/generated-file.dat' ];
+        expect(identify_reviewers_by_changed_files({ config: override_config, changed_files })).to.deep.equal([]);
+      });
+
+      it('returns reviewers when one file matches the wildcard and another is overridden with empty reviewers', function() {
+        const changed_files = [ 'src/main-code.js', 'src/generated-file.dat' ];
+        expect(identify_reviewers_by_changed_files({ config: override_config, changed_files })).to.have.members([ 'alice', 'bob' ]);
+      });
+    });
   });
 
   describe('identify_reviewers_by_author()', function() {