dotnetCorePackages.dotnet_{8..10}.vmr: fallback to bootstrap pre-release with same sdk version

This is necessary because there aren't official releases of all the SDKs
listed in global.json.

pkgs/development/compilers/dotnet/update.nix

@@ -157,8 +157,17 @@ writeScript "update-dotnet-vmr.sh" ''
               "artifactsHash": $_2,
           }' > "${toOutputPath releaseInfoFile}"
 
-      ${lib.escapeShellArg (toOutputPath ./update.sh)} \
-          -o ${lib.escapeShellArg (toOutputPath bootstrapSdkFile)} --sdk "$sdkVersion" >&2
+      updateSDK() {
+          ${lib.escapeShellArg (toOutputPath ./update.sh)} \
+              -o ${lib.escapeShellArg (toOutputPath bootstrapSdkFile)} --sdk "$1" >&2
+      }
+
+      updateSDK "$sdkVersion" || if [[ $? == 2 ]]; then
+          >&2 echo "WARNING: bootstrap sdk missing, attempting to bootstrap with self"
+          updateSDK "$(jq -er .sdkVersion "$tmp"/release.json)"
+      else
+          exit 1
+      fi
 
       $(nix-build -A $UPDATE_NIX_ATTR_PATH.fetch-deps --no-out-link) >&2
   )

pkgs/development/compilers/dotnet/update.sh

@@ -5,6 +5,8 @@
 set -Eeuo pipefail
 shopt -s inherit_errexit
 
+trap 'exit 1' ERR
+
 rids=({linux-{,musl-}{arm,arm64,x64},osx-{arm64,x64},win-{arm64,x64,x86}})
 
 release () {
@@ -225,6 +227,11 @@ usage () {
     echo "Usage: $pname [[--sdk] [-o output] sem-version] ...
 Get updated dotnet src (platform - url & sha512) expressions for specified versions
 
+Exit codes:
+  0 Success
+  1 Failure
+  2 Release not found
+
 Examples:
   $pname 6.0.14 7.0.201    - specific x.y.z versions
   $pname 6.0 7.0           - latest x.y versions
@@ -256,11 +263,13 @@ update() {
     major_minor=$(sed 's/^\([0-9]*\.[0-9]*\).*$/\1/' <<< "$sem_version")
     content=$(curl -fsSL https://dotnetcli.blob.core.windows.net/dotnet/release-metadata/"$major_minor"/releases.json)
     if [[ -n $sdk ]]; then
+        trap '' ERR
         major_minor_patch=$(
             jq -er --arg version "$sem_version" '
                 .releases[] |
                 select(.sdks[].version == $version) |
-                ."release-version"' <<< "$content")
+                ."release-version"' <<< "$content" || if [[ $? == 4 ]]; then exit 2; else exit 1; fi)
+        trap 'exit 1' ERR
     else
         major_minor_patch=$([ "$patch_specified" == true ] && echo "$sem_version" || jq -er '."latest-release"' <<< "$content")
     fi