fix: silent exec (#892)

Unconditionally apply `silent: true` when calling `common.error()` from
`exec()`. This is because errors are already printed to stderr, or are
intentionally silenced by `shell.config.silent`.

Based on #861 

Fixes #851

src/exec.js

@@ -96,7 +96,10 @@ function execSync(cmd, opts, pipe) {
   try { common.unlinkSync(stdoutFile); } catch (e) {}
 
   if (code !== 0) {
-    common.error(stderr, code, { continue: true });
+    // Note: `silent` should be unconditionally true to avoid double-printing
+    // the command's stderr, and to avoid printing any stderr when the user has
+    // set `shell.config.silent`.
+    common.error(stderr, code, { continue: true, silent: true });
   }
   var obj = common.ShellString(stdout, stderr, code);
   return obj;

test/exec.js

@@ -6,14 +6,20 @@ import test from 'ava';
 
 import shell from '..';
 import utils from './utils/utils';
+import mocks from './utils/mocks';
 
 const CWD = process.cwd();
 const ORIG_EXEC_PATH = shell.config.execPath;
 shell.config.silent = true;
 
+test.beforeEach(() => {
+  mocks.init();
+});
+
 test.afterEach.always(() => {
   process.chdir(CWD);
   shell.config.execPath = ORIG_EXEC_PATH;
+  mocks.restore();
 });
 
 //
@@ -85,6 +91,14 @@ test('check if stdout + stderr go to output', t => {
   t.is(result.stderr, '1234\n');
 });
 
+test('check if stdout + stderr should not be printed to console if silent', t => {
+  shell.exec(`${JSON.stringify(shell.config.execPath)} -e "console.error(1234); console.log(666); process.exit(12);"`, { silent: true });
+  const stdout = mocks.stdout();
+  const stderr = mocks.stderr();
+  t.is(stdout, '');
+  t.is(stderr, '');
+});
+
 test('check exit code', t => {
   const result = shell.exec(`${JSON.stringify(shell.config.execPath)} -e "process.exit(12);"`);
   t.truthy(shell.error());