Excessive CPU and memory usage caused by a wrong syntax (unclosed brackets)

[cykuotw]

There is probably an unexpected situation due to unclosed brackets that trigger excessive CPU and memory usage in templ fmt and templ generate.

I have a templ component defined as

templ SplitRule(user types.GroupMember, members []types.GroupMember)

When I call it in another templ file but accidentally forget to close the brackets like:

@SplitRule(types.GroupMember{
    UserID:   uuid.NewString(),
    Username: "user me",
}, []types.GroupMember{
    {
    UserID:   uuid.NewString(),
    Username: "user 1",
    },
// })  <------ should be here but I accidentally forget

There are two cases that can trigger the excessive CPU and memory usage:

1. save the code in VSCode and trigger templ fmt
   • resolve: disable/uninstall templ-vscode vscode plugin and reload vscode
2. use templ generate
   • resolve: kill terminal process

Both of the 2 latest versions can reproduce the problem.

Just in case you want to reproduce it, here is the repo and here is the file

Snapshots

• top -i output,
  
• templ generate -v output
  

templ info output

(✓) os [ goos=linux goarch=amd64 ]
(✓) go [ location=/usr/local/go/bin/go version=go version go1.23.3 linux/amd64 ]
(✓) gopls [ location=/home/cykuotw/go/bin/gopls version=golang.org/x/tools/gopls v0.16.2 ]
(✓) templ [ location=/home/cykuotw/go/bin/templ version=v0.2.793 ]

Desktop:

• OS: WSL Ubuntu 20.04.6 LTS
• templ CLI version: v0.2.793
• Go version: go1.23.3 linux/amd64
• gopls version: golang.org/x/tools/gopls v0.16.2

[a-h]

Thanks for the report. Likely an issue with the parser.

The Go expression parser is here: https://github.com/a-h/templ/tree/main/parser/v2/goexpression
And this is the part that uses the Go parser to parse Go code within templ @SplitRule(...):

templ/parser/v2/templelementparser.go

Line 18 in 9a97564

if r.Expression, err = parseGo("templ element", pi, goexpression.TemplExpression); err != nil {

It should be straightforward to add a test to https://github.com/a-h/templ/blob/main/parser/v2/templelementparser_test.go in order to find it, followed by using the profiler to work out where it's getting stuck.