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cmd/compile: improve error message when if statement brace is on next line #18747

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go101 opened this issue Jan 22, 2017 · 11 comments
Closed

cmd/compile: improve error message when if statement brace is on next line #18747

go101 opened this issue Jan 22, 2017 · 11 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Go1.9

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@go101
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go101 commented Jan 22, 2017 •
edited

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.7.4 linux/amd64

What did you do?

package main

func main() {
	a := 1
	
	for a = 1; a < 2; a++ // syntax error: missing { after for clause
	{
	}
	
	if a == 1 // missing condition in if statement
	{
	}
}

What did you expect to see?

the two error messages should be alike.

What did you see instead?

the the second error message is not very accurate.
@mvdan
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mvdan commented Jan 22, 2017 •
edited

Happens all the same on go version devel +4cce27a3fa Sat Jan 21 03:20:55 2017 +0000 linux/amd64 .

@golang101 perhaps retitle to something like cmd/compile: wrong error when the opening brace of an if is on a new line

@josharian josharian changed the title error message needs improving cmd/compile: improve error message when if statement brace is on next line Jan 22, 2017
@josharian
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@golang101 thanks for filing issues. Would you mind helping the folks doing triage by identifying the relevant component in the issue title, when you know it? Thanks!

cc @odeke-em

@mvdan
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mvdan commented Jan 22, 2017

@josharian did you mean that triage sentence towards me? I haven't requested github access, maybe I should.

@josharian
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It was meant for @golang101. But you should definitely request GitHub access.

@bradfitz bradfitz added this to the Go1.9 milestone Jan 22, 2017
@bradfitz bradfitz added the NeedsFix The path to resolution is known, but the work has not been done. label Jan 22, 2017
@go101
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go101 commented Jan 23, 2017

@josharian I would like to.

@odeke-em odeke-em mentioned this issue Feb 3, 2017
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@gopherbot
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CL https://golang.org/cl/36317 mentions this issue.

@mdempsky
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mdempsky commented Feb 4, 2017

Syntactically,

if foo
{
}

is the same as

if foo; {}

And the latter produces a "missing condition in if statement" error, which is why the former does too.

It's not obvious that the former deserves a different error message; or that if it does, what exactly should be the criteria for producing something different. I'd like to establish that before we worry about CLs.

@bradfitz
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bradfitz commented Feb 4, 2017

@mdempsky, I bet only about 2% of Go users know that semicolons are even in the language at all, much less know the insertion rules.

I personally think it deserves a better error message. A fair number of newcomers to the language are going to write code in that style before they discover gofmt.

@odeke-em
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odeke-em commented Feb 4, 2017

@mdempsky, yeah, I agree with @bradfitz's explanation,
I too think it deserves a better error message.

As we can see in the issue report, the user who reported it found the same problem.

if condition
{
}

wasn't intuitive since visually they already provided the condition a == 1

Getting the same message for

if expression; {
}

that tells me to think about the missing condition in the style

if expression; condition {

even though expression might be a condition.

espadrine added a commit to espadrine/go that referenced this issue Feb 8, 2017
@espadrine
cmd/compile/internal/syntax: improve error message when if statement …
c9a96bc 
…bracec is on next line

For golang#18747.
espadrine added a commit to espadrine/go that referenced this issue Feb 9, 2017
@espadrine
cmd/compile: improve error message when if statement brace is on next…
edbaf79 
… line

A typical beginner mistake is to place the left brace on a new line:

	if condition
	{
		...
	}

Prior to this commit, the error message was misleading:

	missing condition in if statement

Switch to a better error message:

	missing { after if clause

Fixes golang#18747.
@gopherbot
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CL https://golang.org/cl/36930 mentions this issue.

gopherbot pushed a commit that referenced this issue Feb 13, 2017
@griesemer
cmd/compile/internal/syntax: better error for malformed 'if' statements
f823d30 
Use distinction between explicit and automatically inserted semicolons
to provide a better error message if the condition in an 'if' statement
is missing.

For #18747.

Change-Id: Iac167ae4e5ad53d2dc73f746b4dee9912434bb59
Reviewed-on: https://go-review.googlesource.com/36930
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
@griesemer
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This was fixed by https://go-review.googlesource.com/#/c/36930/.

@golang golang locked and limited conversation to collaborators Feb 15, 2018
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@bradfitz @mdempsky @josharian @mvdan @odeke-em @griesemer @gopherbot @go101