reading from file redirection in while loops waits indefinitely

[andrewimeson]

In v3.9.0 of the gosh interpreter there is an issue with reading from file or file substitutions in while loops. The script just hangs when attempting to read from a file or file substitution.

This did work recently. I haven't narrowed down the exact version it broke in yet. I discovered this through it breaking in my Taskfile usage.

Examples

Works: Reading from pipe

#!/usr/bin/env gosh
set -x

echo "hi pipe" | while read -r line; do
    echo "$line"
done

echo "done"

Hangs: Reading from file

#!/usr/bin/env gosh
set -x

echo "hi file" > hi.txt

while read -r line; do
    echo "$line"
done < hi.txt

echo "done"

results in this hanging forever

$ ./while_issue.sh
+ echo 'hi file'
+ read '-r line'
+ echo 'hi file'
hi file
+ read '-r line'

Hangs: Reading from file substitution

#!/usr/bin/env gosh
set -x

while read -r line; do
    echo "$line"
done < <(echo "hi file substitution")

echo done

results in this hanging forever

$ ./while_issue.sh
+ read '-r line'
+ echo 'hi file substitution'
+ echo 'hi file substitution'
hi file substitution
+ read '-r line'

[andrewimeson]

Confirmed that it broke in 3.9.0. It works in 3.8.0.

[andrewimeson]

With git bisect I've determined that #1066 / a89b0be is the commit that broke it.

[andrewimeson]

I tried to write a test that would fail, but I can't seem to get a go test (or a CI run in my fork) to fail with my changes (still fails/hangs with the gosh interpreter). It does fail the CI run for Windows with "TODO: support process substitution on Windows," but I don't care about Windows 😀

diff --git a/interp/interp_test.go b/interp/interp_test.go
index 8b535ce3..4a4e1f2a 100644
--- a/interp/interp_test.go
+++ b/interp/interp_test.go
@@ -2905,6 +2905,10 @@ done <<< 2`,
 		"while read a; do echo $a; GOSH_CMD=exec_ok $GOSH_PROG; done <<EOF\na\nb\nc\nEOF",
 		"a\nexec ok\nb\nexec ok\nc\nexec ok\n",
 	},
+	{
+		"while read a; do echo $a; done < <(echo x)",
+		"x\n",
+	},
 	// TODO: our final exit status here isn't right.
 	// {
 	// 	"while read a; do echo $a; GOSH_CMD=exec_fail $GOSH_PROG; done <<< 'a\nb\nc'",

$ cd interp/
$ go test
PASS
ok  	mvdan.cc/sh/v3/interp	2.808s

[andrewimeson]

Here's a better test that won't run into Windows compatibility issues. I've based off of 3.8.0 and confirmed it passes in CI and it fails in CI for master.

diff --git a/interp/interp_test.go b/interp/interp_test.go
index 8b535ce3..877d8c7a 100644
--- a/interp/interp_test.go
+++ b/interp/interp_test.go
@@ -2905,6 +2905,10 @@ done <<< 2`,
 		"while read a; do echo $a; GOSH_CMD=exec_ok $GOSH_PROG; done <<EOF\na\nb\nc\nEOF",
 		"a\nexec ok\nb\nexec ok\nc\nexec ok\n",
 	},
+	{
+		"echo x > f; while read a; do echo $a; done < f",
+		"x\n",
+	},
 	// TODO: our final exit status here isn't right.
 	// {
 	// 	"while read a; do echo $a; GOSH_CMD=exec_fail $GOSH_PROG; done <<< 'a\nb\nc'",

No idea how to solve the actual bug.