feat(bazel): read binary version info from accompanying files in OCI images instead of stamping //internal/version (#63977)

https://linear.app/sourcegraph/issue/DINF-111/rework-how-we-inject-version-in-our-artifacts

Pros:
- saves having to rebuild `bazel query 'kind("go_library", rdeps(//...,
//internal/version))' | wc -l` == 523 Go packages when stamp variables
cause a rebuild
- Cutting out GoLink action time when stamp changes but code is cached

Cons:
- Binaries themselves are no longer stamped, only knowing their version
info within the context of the docker image
- A tad extra complexity in internal/version/version.go to handle this
new divergence

---

Before:
```
$ bazel aquery --output=summary --include_commandline=false --include_artifacts=false --include_aspects=false --stamp 'inputs(".*volatile-status\.txt", //...)'

  Action: 1
  Genrule: 2
  Rustc: 3
  ConvertStatusToJson: 88
  GoLink: 383
```

After:
```
$ bazel aquery --output=summary --include_commandline=false --include_artifacts=false --include_aspects=false --stamp 'inputs(".*volatile-status\.txt", //...)'

Mnemonics:
  Genrule: 2
  Action: 3
  Rustc: 3
  ConvertStatusToJson: 86
```

## Test plan

Lots of building & rebuilding with stamp flags, comparing execution logs
& times

## Changelog

<!-- OPTIONAL; info at
https://www.notion.so/sourcegraph/Writing-a-changelog-entry-dd997f411d524caabf0d8d38a24a878c
-->

cmd/frontend/image_test.yaml

@@ -20,6 +20,16 @@ fileExistenceTests:
   shouldExist: true
   uid: 100
   gid: 101
+- name: '/version.txt'
+  path: '/version.txt'
+  shouldExist: true
+  uid: 0
+  gid: 0
+- name: '/timestamp.txt'
+  path: '/timestamp.txt'
+  shouldExist: true
+  uid: 0
+  gid: 0
 
 metadataTest:
   envVars:

cmd/server/image_test.yaml

@@ -102,6 +102,16 @@ fileExistenceTests:
   uid: 0
   gid: 0
   permissions: '-rwxrwxrwx'
+- name: '/version.txt'
+  path: '/version.txt'
+  shouldExist: true
+  uid: 0
+  gid: 0
+- name: '/timestamp.txt'
+  path: '/timestamp.txt'
+  shouldExist: true
+  uid: 0
+  gid: 0
 
 metadataTest:
   envVars:

dev/oci_defs.bzl

@@ -26,6 +26,7 @@ def oci_tarball(name, **kwargs):
 def oci_image(name, **kwargs):
     _oci_image(
         name = name + "_underlying",
+        tars = kwargs.pop("tars", []) + ["//internal/version:stamps"],
         **kwargs
     )
 

internal/version/BUILD.bazel

@@ -1,5 +1,7 @@
-load("//dev:go_defs.bzl", "go_test")
+load("@aspect_bazel_lib//lib:expand_template.bzl", "expand_template")
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@rules_pkg//:pkg.bzl", "pkg_tar")
+load("//dev:go_defs.bzl", "go_test")
 
 go_library(
     name = "version",
@@ -7,10 +9,6 @@ go_library(
     importpath = "github.com/sourcegraph/sourcegraph/internal/version",
     tags = [TAG_INFRA_RELEASE],
     visibility = ["//:__subpackages__"],
-    x_defs = {
-        "github.com/sourcegraph/sourcegraph/internal/version.version": "{STABLE_VERSION}",
-        "github.com/sourcegraph/sourcegraph/internal/version.timestamp": "{VERSION_TIMESTAMP}",
-    },
     deps = ["//lib/errors"],
 )
 
@@ -21,3 +19,36 @@ go_test(
     embed = [":version"],
     tags = [TAG_INFRA_RELEASE],
 )
+
+pkg_tar(
+    name = "stamps",
+    srcs = [
+        ":timestamp_file",
+        ":version_file",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+expand_template(
+    name = "version_file",
+    out = "version.txt",
+    stamp_substitutions = {
+        "STABLE_VERSION": "{{STABLE_VERSION}}",
+    },
+    substitutions = {
+        "STABLE_VERSION": "0.0.0+dev",
+    },
+    template = ["STABLE_VERSION"],
+)
+
+expand_template(
+    name = "timestamp_file",
+    out = "timestamp.txt",
+    stamp_substitutions = {
+        "VERSION_TIMESTAMP": "{{VERSION_TIMESTAMP}}",
+    },
+    substitutions = {
+        "VERSION_TIMESTAMP": "",
+    },
+    template = ["VERSION_TIMESTAMP"],
+)

internal/version/version.go

@@ -25,6 +25,16 @@ var LastMinorVersionInMajorRelease = map[int]int{
 }
 
 func init() {
+	versionFromFile, err := os.ReadFile("/version.txt")
+	if err == nil {
+		version = string(versionFromFile)
+	}
+
+	timestampFromFile, err := os.ReadFile("/timestamp.txt")
+	if err == nil && len(timestampFromFile) > 0 {
+		timestamp = string(timestampFromFile)
+	}
+
 	exportedVersion := expvar.NewString("sourcegraph.version")
 	exportedVersion.Set(version)
 }