#265 Warn on redundant semicolon after else by someoneigna · Pull Request #290 · quick-lint/quick-lint-js

someoneigna · 2021-05-13T03:44:03Z

Summary

Warn when a semicolon is found after else.

After this change a warning is reported for the semicolons at 7:7 12:15 and 16:2

let x = 0;
function f() {}
function g() {}

if (x) {
    f();
} else; {
    g();
}


if (x) {} else;
{ }

if (x) {} else
;{ }

Output in VIM plugin format is:

{"qflist": [{"col": 7, "lnum": 7, "end_col": 7, "end_lnum": 7, "type": "W", "nr": "E202", "vcol": 0, "text": "redundant semicolon after else", "filename": "invalid.js"},
{"col": 15, "lnum": 12, "end_col": 15, "end_lnum": 12, "type": "W", "nr": "E202", "vcol": 0, "text": "redundant semicolon after else", "filename": "invalid.js"},
{"col": 1, "lnum": 16, "end_col": 1, "end_lnum": 16, "type": "W", "nr": "E202", "vcol": 0, "text": "redundant semicolon after else", "filename": "invalid.js"}]}

else;;; {} is also valid code but was left out for simplicity. (loop of peek and skip required).

github-actions · 2021-05-13T03:44:47Z

CLA Assistant Lite bot Thank you for your contribution! Like many free software projects, you must sign our Contributor License Agreement before we can accept your contribution.

EDIT: All contributors have signed quick-lint-js' Contributor License Agreement (CLA-v1.md).

someoneigna · 2021-05-13T03:45:44Z

I have read and hereby agree to quick-lint-js' Contributor License Agreement (CLA-v1.md).

src/quick-lint-js/parse.h

src/quick-lint-js/error.h

strager

Minor: It'd also be great if you could add documentation to docs/errors/ for this new error type. Not necessary, though.

src/quick-lint-js/error.h

src/quick-lint-js/parse.h

strager · 2021-05-13T08:26:15Z

src/quick-lint-js/error.h

+  QLJS_ERROR_TYPE(                                                             \
+      error_redundant_semicolon_after_else, "E202",                            \
+      { source_code_span semicolon; },                                         \
+      .warning(QLJS_TRANSLATABLE("redundant semicolon after else"),            \


Blocking: This error message is incorrect. The extra semicolon is not redundant; it changes behavior.

Example:

for (let b of [true, false]) { if (b) { console.log('t'); } else /* Maybe add a semicolon here */ { console.log('f'); } console.log('---'); }

Without semicolon:

t --- f ---

With semicolon:

t f --- f ---

We should communicate that the semicolon is likely unintended, but also imply that removing the semicolon would change behavior.

Perhaps this message is better: "else has empty body; consider removing the semicolon or removing the 'else'" The more I think about it, the more I think we should have two different error messages:

if (b) { } else; { // else has empty body; consider removing the semicolon to make it not empty }

if (b) { } else; // else has empty body; consider removing the redundant 'else' { }

(The first example has no line break between ; and {. The second example does.)

(Perhaps the second case doesn't deserve a diagnostic at all though. Or perhaps it should be of a lesser severity than "warning".)

src/quick-lint-js/parse.h

strager · 2021-05-13T08:29:08Z

test/test-parse-statement.cpp

+    EXPECT_THAT(v.visits, ElementsAre("visit_variable_use",      // cond
+                                      "visit_enter_block_scope",  // (if)
+                                      "visit_variable_use",       // body
+                                      "visit_exit_block_scope")); // (else)


Nit: The comment is misleading. The visit_exit_block_scope is for the if body, not the else body.

Suggested change

"visit_exit_block_scope")); // (else)

"visit_exit_block_scope")); // (if)

src/quick-lint-js/parse.h

docs/errors/E220.md

strager · 2021-05-16T21:50:34Z

docs/errors/E220.md

+    > true
+    > & false
+
+To avoid this behavior, remove the semicolon between the else keyword and the opening brace of the else block.


Include an example of what working code looks like.

docs/errors/E220.md

src/quick-lint-js/parse.h

test/test-parse-statement.cpp

strager · 2021-05-16T21:53:53Z

test/test-parse-statement.cpp

+    EXPECT_THAT(v.errors,
+                ElementsAre(ERROR_TYPE_FIELD(
+                    error_unexpected_semicolon_after_else, semicolon,
+                    offsets_matcher(&code, strlen(u8"if (cond) { body; } else"), u8";"))));


src/quick-lint-js/parse.h

someoneigna · 2021-05-27T00:45:03Z

docs/errors/E202.md

+> else
+```
+
+To avoid this behavior, remove the semicolon between the else keyword and the opening brace of the else block.


Maybe:
In case this is impacting your code, you should remove the semicolon next to the else keyword

someoneigna · 2021-05-27T00:50:30Z

src/quick-lint-js/parse.h

+      if (this->peek().type == token_type::right_curly) {
+        this->error_reporter_->report(error_else_has_empty_body{
+            .where = source_code_span(expect_left_curly.begin, this->peek().end)
+        });
+      } else if (token_after_else.type == token_type::semicolon &&


This is the check for an empty block on the else case. Now that I read it again, I see it should only be triggered if the else has a semicolon 🤦‍♂️
#290 (comment)

Is creating a transaction on the lexer and then rolling it back the correct way to peek forward?

Is creating a transaction on the lexer and then rolling it back the correct way to peek forward?

We only need a transaction if you want to look ahead multiple tokens.

Can you give an example JS program where using this->peek() won't work?

I had gone through a rabbit hole of actually checking the body of the next scope to the else. That's why I was advancing the cursor and parsing the next scope after the else using a transaction 🤦‍♂️ . I've rolled the code back to only check for the newline and the opening brace.
Commits are now squashed, let me know what you think.

strager · 2021-05-27T08:00:29Z

Did you want me to review your latest changes, or are you still hacking?

src/quick-lint-js/error.h

strager

Thanks for the update. The logic looks much cleaner now!

strager · 2021-06-10T08:07:40Z

docs/errors/E204.md

+    if (true) {
+        console.log("true");
+    }
+    console.log("always");


Lovely docs!

strager · 2021-06-10T08:12:30Z

test/test-parse-statement.cpp

+            offsets_matcher(&code, strlen(u8"if (cond) { body; } else {"),
+                            u8"}"))));


Blocking: This strlen string doesn't match the code. The u8"}" looks wrong too. Did you mean the following instead?

Suggested change

offsets_matcher(&code, strlen(u8"if (cond) { body; } else {"),

u8"}"))));

offsets_matcher(&code, strlen(u8"if (cond) { body; } else;\n"),

u8"{"))));

If so, the error looks misplaced. It should point at the else token or the ;, not at the following unrelated {.

Right now it detects else;{} (semicolon after else) and else;\n{} (empty body), the following in parse.h:2534 should change to only trigger else has empty body when it is not preceded by a newline:

- if (token_after_else.type == token_type::semicolon && - this->peek().type == token_type::left_curly) { + if (token_after_else.type == token_type::semicolon && + this->peek().type == token_type::left_curly && + !this->peek().has_leading_newline) { - if (this->peek().has_leading_newline) { + if (body is empty) { this->error_reporter_->report( error_else_has_empty_body{.where = this->peek().span()}); } else { this->error_reporter_->report(error_unexpected_semicolon_after_else{ .semicolon = token_after_else.span()}); } }

Should I omit the else has empty body warning altogether, or should I detect the empty body?
I do not know how to do it without making use of a transaction, advancing the peek and then doing a rollback afterwards.

Should I omit the else has empty body warning altogether

Yeah, let's only emit error_unexpected_semicolon_after_else in this PR.

I do not know how to do it without making use of a transaction, advancing the peek and then doing a rollback afterwards.

Would something like this work? Or am I missing an edge case?

if (token_after_else.type == token_type::semicolon && this->peek().type == token_type::left_curly && !this->peek().has_leading_newline) { this->error_reporter_->report(error_unexpected_semicolon_after_else{ .semicolon = token_after_else.span(), }); }

strager · 2021-06-10T08:13:51Z

test/test-parse-statement.cpp

+TEST(test_parse, else_has_empty_body) {
+  {
+    spy_visitor v;
+    padded_string code(u8"if (cond) { body; } else;\n{ }"_sv);


Nit: I don't think it's worth having a diagnostic for this code. If there's a newline after the else;, I think the empty body is intentional.

strager · 2021-06-25T04:39:07Z

docs/errors/E204.md

@@ -0,0 +1,30 @@
+# E204: semicolon after else may be causing unexpected behavior.


Someone else took error code E204. Choose a different error code.

someoneigna commented May 13, 2021

View reviewed changes

src/quick-lint-js/parse.h Outdated Show resolved Hide resolved

someoneigna commented May 13, 2021

View reviewed changes

src/quick-lint-js/error.h Outdated Show resolved Hide resolved

strager mentioned this pull request May 13, 2021

9$: Warn on semicolon in if-else chain #265

Open

strager linked an issue May 13, 2021 that may be closed by this pull request

9$: Warn on semicolon in if-else chain #265

Open

strager requested changes May 13, 2021

View reviewed changes

someoneigna force-pushed the warn-else-semicolon branch from a4ce1c3 to 82917f4 Compare May 16, 2021 21:37

someoneigna commented May 16, 2021

View reviewed changes

src/quick-lint-js/parse.h Outdated Show resolved Hide resolved

strager requested changes May 16, 2021

View reviewed changes

someoneigna commented May 27, 2021

View reviewed changes

strager requested changes May 27, 2021

View reviewed changes

src/quick-lint-js/error.h Outdated Show resolved Hide resolved

someoneigna force-pushed the warn-else-semicolon branch 4 times, most recently from 0b6c261 to 81acb09 Compare June 8, 2021 05:16

Warn for possible unexpected behavior when else followed by a semicolon.

79d5928

someoneigna force-pushed the warn-else-semicolon branch from 81acb09 to 79d5928 Compare June 9, 2021 03:02

strager requested changes Jun 10, 2021

View reviewed changes

strager reviewed Jun 25, 2021

View reviewed changes

	"visit_exit_block_scope")); // (else)
	"visit_exit_block_scope")); // (if)

		offsets_matcher(&code, strlen(u8"if (cond) { body; } else {"),
		u8"}"))));

		@@ -0,0 +1,30 @@
		# E204: semicolon after else may be causing unexpected behavior.

Uh oh!

Conversation

someoneigna commented May 13, 2021

Summary

Uh oh!

github-actions bot commented May 13, 2021 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

someoneigna commented May 13, 2021

Uh oh!

Uh oh!

Uh oh!

strager left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

strager commented May 27, 2021

Uh oh!

Uh oh!

strager left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

github-actions bot commented May 13, 2021 •

edited

Loading