cmd/compile: -embedcfg flag is undocumented

[pjebs]

Go version

go 1.24.0

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/x/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/x/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/15/70nsj6sx3ln38_59dth_0p2w0000gn/T/go-build897804675=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/x/Documents/compiler/go.mod'
GOMODCACHE='/Users/x/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/x/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/Cellar/go/1.24.0/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/x/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/Cellar/go/1.24.0/libexec/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.24.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I have a sub-package (hence no go.mod):

=== name.txt ===
X-MEN

=== sub.go ===
package sub

import _ "embed"


//go:embed name.txt
var Name string

I ran go tool compile -importcfg importcfg

=== importcfg ===
packagefile internal/goarch=/Users/x/Library/Caches/go-build/f6/f65dfbc44b7fc3256f82a913154e9b346ba39604d4215d25ea8209ca7a06c414-d
packagefile internal/abi=/Users/x/Library/Caches/go-build/e8/e81f4d153c4ecd6e5a65208601c8d7b94e22bdc6dfc9a9d8748f7f96835a1288-d
packagefile internal/unsafeheader=/Users/x/Library/Caches/go-build/30/30ae79d8bb02cb48dc8dfb22d8c6fe566f053f19ed48807ee4afb4f17d9c79ec-d
packagefile internal/cpu=/Users/x/Library/Caches/go-build/1d/1dc1423b7d1cd33482d1bb462938442063f34f6d6cfc4658c9aac7fba32528a1-d
packagefile internal/bytealg=/Users/x/Library/Caches/go-build/af/af0d8e7da0088e05c6f21b664e4490c0b9eae31056211781a7bb569bc8ce34f3-d
packagefile internal/byteorder=/Users/x/Library/Caches/go-build/e3/e31305e922cc6b0824d91a1e6dc86fe28bbe0faeb5002d4632f36a142fba6608-d
packagefile internal/chacha8rand=/Users/x/Library/Caches/go-build/62/62472955c90055aa6f4aafd26ddfb7b17cabcc56cb3d996ce127438dc6847b92-d
packagefile internal/coverage/rtcov=/Users/x/Library/Caches/go-build/e9/e936ae6477e50e97428eb73a547c464b50438547fd00f3ec9816f6e0089726b2-d
packagefile internal/godebugs=/Users/x/Library/Caches/go-build/ca/ca53f641aa6f01f90c272e67cd032e5b7dad14a3327dad0bee410d9817ed70d4-d
packagefile internal/goexperiment=/Users/x/Library/Caches/go-build/02/02740d9b59da9f160fee17509acc6fbffcd50981a9364d2b250cc718bff68be6-d
packagefile internal/goos=/Users/x/Library/Caches/go-build/f8/f855b7b73cf8645d28b92a304a809410272b7f183c39afaeb3390ac9c1ed0b9c-d
packagefile internal/profilerecord=/Users/x/Library/Caches/go-build/cb/cbb1ebb0e2cb64d1161550a7960df855213d7d5976668bf9b136e83f1d187a3d-d
packagefile internal/runtime/atomic=/Users/x/Library/Caches/go-build/fe/fe1bd249d67e1a9b521c2957d966ec1181f2c696c3cf3f5ca80130b043bab0c3-d
packagefile internal/runtime/exithook=/Users/x/Library/Caches/go-build/1f/1f7313f524c9bdec913b683bb93120ce7e8b11697e4b195821bf40b5775cad78-d
packagefile internal/asan=/Users/x/Library/Caches/go-build/7d/7dad48e87431f736bb3b1acdcaaba7bd954049d91e0848fc4f07337807e800fd-d
packagefile internal/msan=/Users/x/Library/Caches/go-build/19/1902c3631e862edd6e17f63581f5d4939f387a5252bcab5bc5a4ed9cea013184-d
packagefile internal/race=/Users/x/Library/Caches/go-build/9d/9d0b0b84d24764133b8bc3c45505b7904236a2066a3320cb5883df5c946bc405-d
packagefile internal/runtime/math=/Users/x/Library/Caches/go-build/5a/5abaef58cc2f484eae13611c76ba8a3a95447e86c0d99de0fb11d6e4aeb95614-d
packagefile internal/runtime/sys=/Users/x/Library/Caches/go-build/23/23a5ce86acee3b8b62cd4a6d6ecccb05e42e874930ff3595a93041f16180f0d7-d
packagefile internal/runtime/maps=/Users/x/Library/Caches/go-build/15/1596bb4293372ac631b092ee7ba7bac21750a5ab48e8e7d2eab9cbc95b380d19-d
packagefile internal/stringslite=/Users/x/Library/Caches/go-build/c9/c972a2d0d193ba8cf5f3aa1c9d532fd843c94ab61c308a32986256154d8ce138-d
packagefile runtime=/Users/x/Library/Caches/go-build/d4/d4e452e1de6af1745a89ea54aa79be9981095e05f2af7ea40a677aa3c0e4d283-d
packagefile internal/reflectlite=/Users/x/Library/Caches/go-build/a1/a161093bc46e0fb4c4892a246a0b4e01be09906f0569a4ccf588e7731562175e-d
packagefile errors=/Users/x/Library/Caches/go-build/29/298afc218eff7183e2e0f4b3f064aaed72c7d2676fa1f3b255f3eebb62870f95-d
packagefile sync/atomic=/Users/x/Library/Caches/go-build/69/695b76f5d8491e0db427cfeec117cf33e429e6de77dd6d1cdb421414c259ba91-d
packagefile internal/sync=/Users/x/Library/Caches/go-build/81/81490f1daaf2269e415d03d315fc7aea3010aaee2b187acc004da84bd16e6f4c-d
packagefile sync=/Users/x/Library/Caches/go-build/22/226b41001111550658ef9252c3aa17ad49217d534e128f7a9d797325af3f94b7-d
packagefile io=/Users/x/Library/Caches/go-build/27/275c6b54095daf676f8bce5c9c163aa713581bcedff1755c11c230c4ec197b4d-d
packagefile internal/oserror=/Users/x/Library/Caches/go-build/84/843f5514d617999f66d552914cb5e694b0be6a5914cb250ecd30c097b9513cda-d
packagefile unicode/utf8=/Users/x/Library/Caches/go-build/c3/c3d780b02dd4c29ccb0866def62a5ed6ea46cc3c25b71f84c49e8e392997b022-d
packagefile path=/Users/x/Library/Caches/go-build/76/76cf82bbce3b17890d46aaf5a9d6bd472522138b712167c08fd9cc7f7a52a45f-d
packagefile cmp=/Users/x/Library/Caches/go-build/68/68a77cfe6dd685c840ceca81453a4351aabdae8033d4a838df2e27c7fc9544b5-d
packagefile iter=/Users/x/Library/Caches/go-build/77/77840c3b8b6e578efd7fc68dab2467ed0abb847424d93bba2e886b443e56cbda-d
packagefile math/bits=/Users/x/Library/Caches/go-build/28/28fa9b5ca6ef50f443e2da99f46858ac7d9b344a8d7ec47c026f97c0598fdd4d-d
packagefile slices=/Users/x/Library/Caches/go-build/e0/e069f94148905826fa9dfbff5405927252a6498f4e71fba5069c658f3d3a3733-d
packagefile internal/bisect=/Users/x/Library/Caches/go-build/a0/a014bbe344c982107d70bc446e37b9ce8a5494f4370ee841a32da9e80d4d1541-d
packagefile internal/godebug=/Users/x/Library/Caches/go-build/2a/2a88c366f381329f249f9be40c7d05939e5d49278e2ce96d0823f8703de9eac8-d
packagefile internal/itoa=/Users/x/Library/Caches/go-build/5d/5d82ffc935c498db3ff85d57b0f4339755b543f9d619d166a25677bb76d8d40a-d
packagefile syscall=/Users/x/Library/Caches/go-build/cb/cb0339b99962e3289e196e461df7ee2ca197f5a9689b3947adeb1e77c8f4a32b-d
packagefile time=/Users/x/Library/Caches/go-build/f2/f2702e22ca4bd59ab326cf9cb8f339abf3570a65b528185116fc754e253377e2-d
packagefile io/fs=/Users/x/Library/Caches/go-build/0f/0fe00edcf1c24f7463232934fe6109de6fb94d7b58fe0dbf5192078d303ef4ad-d
packagefile embed=/Users/x/Library/Caches/go-build/82/82605b3dd8baaceebca51df7fd6ad8e0a3c4ef3fbf8c8ef2d0351074adda24bb-d
packagefile test/plugin/sub/tmp1671232560/src=/Users/x/Library/Caches/go-build/a4/a4a3c6fcafa07452587656b00f9446c00bab5e6444612b22bd21cdb13eefbb48-d

What did you see happen?

Error:

invalid go:embed: build system did not supply embed configuration

What did you expect to see?

I expected it to successfully compile and produce an *.o or *.a file.

Running it with go build ... works. It successfully sees the file and embeds it.

If it's not allowed, the https://pkg.go.dev/cmd/compile documentation should make note of that.

NOTE: When I remove the embed directive, it works.

[gabyhelp]

Related Issues

• cmd/go: Setting up a go workspace breaks building #57738 (closed)
• x/tools/internal/imports: import embed in files containing go:embed directives #50414
• GOARCH=arm64 go build can't find imports #68007 (closed)
• x/tools/gopls: make go.mod diagnostics on mismatched requirements available when go.work is used #48920
• Embed is not working #48352 (closed)
• Test #67906 (closed)
• embed: failed to build source file contains string "/*" #43373 (closed)
• x/tools/cmd/gopls: fails on filepaths with spaces #34270 (closed)
• cmd/go: `mod vendor` tries to evaluate go:embed pattern inside _test.go files #63473 (closed)
• x/tools/gopls: negated build flag causes error #59346

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/652475 mentions this issue: cmd/compile: document -embedcfg flag

[pjebs]

@ianlancetaylor Your change:

-embedcfg file
		Read go:embed configuration from file.
		This is required if any //go:embed directives are used.
		The file is a JSON file mapping patterns to lists of filenames
		and filenames to full path names.

I can't see a section called go:embed configuration from file. in https://pkg.go.dev/cmd/compile

or "import configuration from file" for that matter

[ianlancetaylor]

Those sections don't exist. This is user documentation, not developer documentation. We aren't going to provide user documentation for these files, because we reserve the right to change their format over time.