fix: saveCache shouldn't error on existing cache, warn instead

.github/workflows/example-basic.yml

@@ -1,5 +1,5 @@
 name: example-basic
-on: [push]
+on: [push, pull_request]
 jobs:
   test:
     runs-on: ubuntu-latest

.github/workflows/example-subfolders.yml

@@ -1,5 +1,5 @@
 name: example-subfolders
-on: [push]
+on: [push, pull_request]
 jobs:
   separate-actions:
     runs-on: ${{ matrix.os }}

.github/workflows/example-without-lock-file.yml

@@ -1,5 +1,5 @@
 name: example-without-lock-file
-on: [push]
+on: [push, pull_request]
 jobs:
   test:
     runs-on: ubuntu-latest

.github/workflows/example-yarn.yml

@@ -1,5 +1,5 @@
 name: example-yarn
-on: [push]
+on: [push, pull_request]
 jobs:
   test:
     runs-on: ubuntu-latest

.github/workflows/main.yml

@@ -1,5 +1,5 @@
 name: main
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build-and-test:

dist/index.js

@@ -2756,7 +2756,19 @@ const restoreCachedNpm = npmCache => {
 
 const saveCachedNpm = npmCache => {
   console.log('saving NPM modules')
-  return cache.saveCache(npmCache.inputPaths, npmCache.primaryKey)
+
+  return cache
+    .saveCache(npmCache.inputPaths, npmCache.primaryKey)
+    .catch(err => {
+      // don't throw an error if cache already exists, which may happen due to
+      // race conditions
+      if (err.message.includes('Cache already exists')) {
+        console.warn(err.message)
+        return -1
+      }
+      // otherwise re-throw
+      throw err
+    })
 }
 
 const hasOption = (name, o) => name in o

index.js

@@ -38,7 +38,19 @@ const restoreCachedNpm = npmCache => {
 
 const saveCachedNpm = npmCache => {
   console.log('saving NPM modules')
-  return cache.saveCache(npmCache.inputPaths, npmCache.primaryKey)
+
+  return cache
+    .saveCache(npmCache.inputPaths, npmCache.primaryKey)
+    .catch(err => {
+      // don't throw an error if cache already exists, which may happen due to
+      // race conditions
+      if (err.message.includes('Cache already exists')) {
+        console.warn(err.message)
+        return -1
+      }
+      // otherwise re-throw
+      throw err
+    })
 }
 
 const hasOption = (name, o) => name in o