Test stdlib-bootstrapped TASTy-MiMa in CI (#18158)

This addition does have some fragility with the current TASTy numbering
scheme. The test script will change the TASTy version and recompile the
compiler and library with this version to allow TASTy MiMa to read those
files.

When we change to a new major version, there is the potential for this
TASTy to not be readable from the latest release of TASTy MiMa. In that
scenario, we would disable this test until a new version of TASTy MiMa
is published.

.github/workflows/ci.yaml

@@ -255,6 +255,11 @@ jobs:
         run: |
           ./project/scripts/sbt ";scala3-interfaces/mimaReportBinaryIssues ;scala3-library-bootstrapped/mimaReportBinaryIssues ;scala3-library-bootstrappedJS/mimaReportBinaryIssues; tasty-core-bootstrapped/mimaReportBinaryIssues; stdlib-bootstrapped/mimaReportBinaryIssues"
 
+      - name: TASTy MiMa
+        run: |
+          # This script cleans the compiler and recompiles it from scratch (keep as last run)
+          ./project/scripts/stdlib-bootstrapped-tasty-mima.sh
+
   community_build_a:
     runs-on: [self-hosted, Linux]
     container:

project/scripts/stdlib-bootstrapped-tasty-mima.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+set -eux
+
+source $(dirname $0)/cmdTestsCommon.inc.sh
+
+TASTY_FROMAT_FILE="tasty/src/dotty/tools/tasty/TastyFormat.scala"
+MINOR_TASTY_VERSION_SUPPORTED_BY_TASTY_MIMA=3
+MINOR_TASTY_VERSION=$(grep -oE 'val MinorVersion: Int = ([0-9]+)' $TASTY_FROMAT_FILE | grep -oE '[0-9]+')
+EXPERIMENTAL_TASTY_VERSION=$(grep -oE 'val ExperimentalVersion: Int = ([0-9]+)' $TASTY_FROMAT_FILE | grep -oE '[0-9]+')
+
+setTastyVersion() {
+  sed -i -E -e "s/val MinorVersion: Int = [0-9]+/val MinorVersion: Int = $1/" -e "s/val ExperimentalVersion: Int = [0-9]+/val ExperimentalVersion: Int = $2/" $TASTY_FROMAT_FILE
+}
+
+setTastyVersion $MINOR_TASTY_VERSION_SUPPORTED_BY_TASTY_MIMA 0
+
+# Run stdlib-bootstrapped/tastyMiMaReportIssues using a custom TASTy version.
+# We clean before to make sure all sources are recompiled using the new TASTY version.
+# We clean after to make sure no other test will use the TASTy generated with this version.
+"$SBT" "clean; stdlib-bootstrapped/clean; reload; stdlib-bootstrapped/tastyMiMaReportIssues; clean; stdlib-bootstrapped/clean"
+
+setTastyVersion $MINOR_TASTY_VERSION $EXPERIMENTAL_TASTY_VERSION