x/pkgsite: panic for some packages with syntax errors with locally running pkgsite #73377
Description
What is the URL of the page with the issue?
http://localhost:8080/github.com/mjl-/mox
What is your user agent?
firefox (not relevant)
Screenshot
The connection was reset
The connection to the server was reset while the page was loading.
What did you do?
To reproduce, create a local directory somewhere, with two files (the form of the module path seems relevant):
$ cat go.mod
module github.com/mjl-/mox
go 1.24.2
Malformed go file:
$ cat test.go
package test
bad
Run latest pkgsite:
go run -trimpath golang.org/x/pkgsite/cmd/pkgsite@v0.0.0-20250414131012-01dc430a4e83
Open http://localhost:8080/github.com/mjl-/mox
What did you see happen?
An error message about the invalid package.
What did you expect to see?
An aborted HTTP request due to an unhandled panic of a nil pointer dereference:
2025/04/14 20:58:29 Warning: fetching url from deps.dev: Get "https://deps.dev/_/s/go/p/github.com%2Fmjl-%2Fmox/v/v0.0.0/exists": context canceled
2025/04/14 20:58:29 http: panic serving 127.0.0.1:55874: runtime error: invalid memory address or nil pointer dereference
goroutine 697 [running]:
net/http.(*conn).serve.func1()
net/http/server.go:1947 +0xbe
panic({0xb84260?, 0x1708220?})
runtime/panic.go:792 +0x132
golang.org/x/pkgsite/internal/fetchdatasource.(*FetchDataSource).populateUnitSubdirectories(...)
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/fetchdatasource/fetchdatasource.go:161
golang.org/x/pkgsite/internal/fetchdatasource.(*FetchDataSource).findUnit(0xc0002f8fc0, {0x124a100?, 0xc000333ce0?}, 0xc000486000, {0xc000416000?, 0xc4cf01?})
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/fetchdatasource/fetchdatasource.go:233 +0x65
golang.org/x/pkgsite/internal/fetchdatasource.(*FetchDataSource).GetUnit(0xc0002f8fc0, {0x124a100, 0xc000333ce0}, 0xc0003485a0, 0x49dd59?, {{0x0?, 0xc00087abb0?}, {0x0?, 0x49dd9e?}})
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/fetchdatasource/fetchdatasource.go:214 +0x17f
golang.org/x/pkgsite/internal/frontend.fetchMainDetails({0x124a100, 0xc000333ce0}, {0x124d620, 0xc0002f8fc0}, 0xc0003485a0, {0xc4ced7, 0x6}, 0x0, {{0x0, 0x0}, ...})
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/frontend/main.go:117 +0x16d
golang.org/x/pkgsite/internal/frontend.fetchDetailsForUnit({0x124a100, 0xc000333ce0}, 0xc00040d040, {0x0, 0x0}, {0x124d620, 0xc0002f8fc0}, 0xc0003485a0, {0xc4ced7, 0x6}, ...)
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/frontend/tabs.go:87 +0x305
golang.org/x/pkgsite/internal/frontend.(*Server).serveUnitPage(0xc00079ca20, {0x124a100, 0xc000333ce0}, {0x1248878, 0xc000712380}, 0xc00040d040, {0x124d620, 0xc0002f8fc0}, 0xc002746510)
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/frontend/unit.go:147 +0x3a8
golang.org/x/pkgsite/internal/frontend.(*Server).serveDetails(0xc00079ca20, {0x1248878, 0xc000712380}, 0xc00040d040, {0x124d620, 0xc0002f8fc0})
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/frontend/details.go:72 +0x691
golang.org/x/pkgsite/internal/frontend.(*Server).Install.(*Server).errorHandler.func6({0x1248878, 0xc000712380}, 0xc00040d040)
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/frontend/server.go:504 +0x6c
net/http.HandlerFunc.ServeHTTP(0xc0000d83c0?, {0x1248878?, 0xc000712380?}, 0x6e9b4f?)
net/http/server.go:2294 +0x29
net/http.(*ServeMux).ServeHTTP(0xc00040cf00?, {0x1248878, 0xc000712380}, 0xc00040d040)
net/http/server.go:2822 +0x1c4
main.main.main.Timeout.func3.func4({0x1248878, 0xc000712380}, 0xc00040cf00)
golang.org/x/pkgsite@v0.0.0-20250414131012-01dc430a4e83/internal/middleware/timeout/timeout.go:20 +0x94
net/http.HandlerFunc.ServeHTTP(0x476739?, {0x1248878?, 0xc000712380?}, 0xc001807b70?)
net/http/server.go:2294 +0x29
net/http.serverHandler.ServeHTTP({0xc002746420?}, {0x1248878?, 0xc000712380?}, 0x6?)
net/http/server.go:3301 +0x8e
net/http.(*conn).serve(0xc0000e73b0, {0x124a058, 0xc0008aae70})
net/http/server.go:2102 +0x625
created by net/http.(*Server).Serve in goroutine 1
net/http/server.go:3454 +0x485
The nil pointer dereference is at https://github.com/golang/pkgsite/blob/01dc430a4e8339c44b283f075264c5c5dd47621c/internal/fetchdatasource/fetchdatasource.go#L161
The nil u is coming from https://github.com/golang/pkgsite/blob/01dc430a4e8339c44b283f075264c5c5dd47621c/internal/fetchdatasource/fetchdatasource.go#L233 (nil unit)