repl: make last error available as _error

This is pretty useful when trying to inspect the last
error caught by a REPL, and is made to be analogous to `_`,
which contains the last successful completion value.

PR-URL: https://github.com/nodejs/node/pull/18919
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
This commit is contained in:
Anna Henningsen 2018-02-21 21:50:20 +01:00
parent 648d668fcc
commit a8b5192fef
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3 changed files with 103 additions and 0 deletions

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@ -142,6 +142,12 @@ global or scoped variable, the input `fs` will be evaluated on-demand as
``` ```
#### Assignment of the `_` (underscore) variable #### Assignment of the `_` (underscore) variable
<!-- YAML
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/18919
description: Added `_error` support.
-->
The default evaluator will, by default, assign the result of the most recently The default evaluator will, by default, assign the result of the most recently
evaluated expression to the special variable `_` (underscore). evaluated expression to the special variable `_` (underscore).
@ -162,6 +168,17 @@ Expression assignment to _ now disabled.
4 4
``` ```
Similarly, `_error` will refer to the last seen error, if there was any.
Explicitly setting `_error` to a value will disable this behavior.
<!-- eslint-skip -->
```js
> throw new Error('foo');
Error: foo
> _error.message
'foo'
```
### Custom Evaluation Functions ### Custom Evaluation Functions
When a new `repl.REPLServer` is created, a custom evaluation function may be When a new `repl.REPLServer` is created, a custom evaluation function may be

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@ -156,6 +156,8 @@ function REPLServer(prompt,
self.replMode = replMode || exports.REPL_MODE_SLOPPY; self.replMode = replMode || exports.REPL_MODE_SLOPPY;
self.underscoreAssigned = false; self.underscoreAssigned = false;
self.last = undefined; self.last = undefined;
self.underscoreErrAssigned = false;
self.lastError = undefined;
self.breakEvalOnSigint = !!breakEvalOnSigint; self.breakEvalOnSigint = !!breakEvalOnSigint;
self.editorMode = false; self.editorMode = false;
// Context id for use with the inspector protocol. // Context id for use with the inspector protocol.
@ -388,6 +390,8 @@ function REPLServer(prompt,
internalUtil.decorateErrorStack(e); internalUtil.decorateErrorStack(e);
Error.prepareStackTrace = pstrace; Error.prepareStackTrace = pstrace;
const isError = internalUtil.isError(e); const isError = internalUtil.isError(e);
if (!self.underscoreErrAssigned)
self.lastError = e;
if (e instanceof SyntaxError && e.stack) { if (e instanceof SyntaxError && e.stack) {
// remove repl:line-number and stack trace // remove repl:line-number and stack trace
e.stack = e.stack e.stack = e.stack
@ -796,6 +800,7 @@ REPLServer.prototype.createContext = function() {
REPLServer.prototype.resetContext = function() { REPLServer.prototype.resetContext = function() {
this.context = this.createContext(); this.context = this.createContext();
this.underscoreAssigned = false; this.underscoreAssigned = false;
this.underscoreErrAssigned = false;
this.lines = []; this.lines = [];
this.lines.level = []; this.lines.level = [];
@ -811,6 +816,19 @@ REPLServer.prototype.resetContext = function() {
} }
}); });
Object.defineProperty(this.context, '_error', {
configurable: true,
get: () => this.lastError,
set: (value) => {
this.lastError = value;
if (!this.underscoreErrAssigned) {
this.underscoreErrAssigned = true;
this.outputStream.write(
'Expression assignment to _error now disabled.\n');
}
}
});
// Allow REPL extensions to extend the new context // Allow REPL extensions to extend the new context
this.emit('reset', this.context); this.emit('reset', this.context);
}; };

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@ -10,6 +10,7 @@ testStrictMode();
testResetContext(); testResetContext();
testResetContextGlobal(); testResetContextGlobal();
testMagicMode(); testMagicMode();
testError();
function testSloppyMode() { function testSloppyMode() {
const r = initRepl(repl.REPL_MODE_SLOPPY); const r = initRepl(repl.REPL_MODE_SLOPPY);
@ -153,6 +154,73 @@ function testResetContextGlobal() {
delete global.require; delete global.require;
} }
function testError() {
const r = initRepl(repl.REPL_MODE_STRICT);
r.write(`_error; // initial value undefined
throw new Error('foo'); // throws error
_error; // shows error
fs.readdirSync('/nonexistent?'); // throws error, sync
_error.code; // shows error code
_error.syscall; // shows error syscall
setImmediate(() => { throw new Error('baz'); }); undefined;
// throws error, async
`);
setImmediate(() => {
const lines = r.output.accum.trim().split('\n');
const expectedLines = [
'undefined',
// The error, both from the original throw and the `_error` echo.
'Error: foo',
'Error: foo',
// The sync error, with individual property echoes
/Error: ENOENT: no such file or directory, scandir '.*nonexistent.*'/,
/fs\.readdirSync/,
"'ENOENT'",
"'scandir'",
// Dummy 'undefined' from the explicit silencer + one from the comment
'undefined',
'undefined',
// The message from the original throw
'Error: baz',
/setImmediate/,
/^ at/,
/^ at/,
/^ at/,
/^ at/,
];
for (const line of lines) {
const expected = expectedLines.shift();
if (typeof expected === 'string')
assert.strictEqual(line, expected);
else
assert(expected.test(line), `${line} should match ${expected}`);
}
assert.strictEqual(expectedLines.length, 0);
// Reset output, check that '_error' is the asynchronously caught error.
r.output.accum = '';
r.write(`_error.message // show the message
_error = 0; // disable auto-assignment
throw new Error('quux'); // new error
_error; // should not see the new error
`);
assertOutput(r.output, [
"'baz'",
'Expression assignment to _error now disabled.',
'0',
'Error: quux',
'0'
]);
});
}
function initRepl(mode, useGlobal) { function initRepl(mode, useGlobal) {
const inputStream = new stream.PassThrough(); const inputStream = new stream.PassThrough();
const outputStream = new stream.PassThrough(); const outputStream = new stream.PassThrough();