Add a build check for PRs (AssemblyScript#51)

This now checks that distribution files are unmodified and fails otherwise. Also checks if the author is present in the NOTICE file and prints the result, but as email addresses may vary, does not hard-fail.

.gitattributes

@@ -1,3 +1,4 @@
 bin/asc text eol=lf
 dist/asc.js -diff
 dist/assemblyscript.js -diff
+scripts/check-pr.sh eol=lf

.travis.yml

@@ -1,7 +1,17 @@
 language: node_js
+notifications:
+  email: false
+stages:
+  - name: check-pr
+    if: type = pull_request
 jobs:
   include:
 
+  - stage: check-pr
+    node_js: lts/*
+    script: ./scripts/check-pr.sh
+    env: Checks contributing guidelines before testing pull requests
+
   - stage: lint
     node_js: node
     script: npm run lint

scripts/check-pr.sh

@@ -0,0 +1,29 @@
+# Distribution files should not be modified
+STATUS=0
+if git --no-pager diff --name-only FETCH_HEAD $(git merge-base FETCH_HEAD $TRAVIS_BRANCH) | grep -q "^dist/"; then
+  STATUS=1 &&
+  printf "\n" &&
+  printf "The pull request includes changes to distribution files, but it shouldn't.\n" &&
+  printf "Please see https://github.com/AssemblyScript/assemblyscript/blob/master/CONTRIBUTING.md\n";
+else
+  printf "\n" &&
+  printf "GOOD: The pull request does not include changes to distribution files.\n";
+fi
+
+# Authors should have added themself to the NOTICE file
+AUTHOR=$(git log -1 --format="%aE")
+if [ -z "$AUTHOR" ]; then
+  printf "\n" &&
+  printf "Skipping NOTICE check: Commit does not include an email address.\n";
+else
+  if grep -q "$AUTHOR" NOTICE; then
+    printf "\n" &&
+    printf "GOOD: Author is present in the NOTICE file.\n";
+  else
+    printf "\n" &&
+    printf "Author does not appear to be listed in the NOTICE file, yet.\n" &&
+    printf "Please see https://github.com/AssemblyScript/assemblyscript/blob/master/CONTRIBUTING.md\n";
+  fi
+fi
+
+exit $STATUS

src/types.ts

@@ -541,7 +541,7 @@ export class Signature {
     // check return type
     var thisReturnType = this.returnType;
     var targetReturnType = target.returnType;
-    return thisReturnType == targetReturnType || this.returnType.isAssignableTo(target.returnType);
+    return thisReturnType == targetReturnType || thisReturnType.isAssignableTo(targetReturnType);
   }
 
   /** Converts this signature to a function type string. */