Error out on fetch operations on CVS/Git mismatch

Now that we support two SCMs, make sure we don't use the wrong one on
an existing copy of the src and xsrc checkouts.  This will avoid some
user errors.

sysbuild.sh

@@ -309,28 +309,53 @@ sysbuild_fetch() {
         cvs)
             local cvsroot="$(shtk_config_get CVSROOT)"
 
+            local srcdir="$(shtk_config_get SRCDIR)"
+            if [ -d "${srcdir}" -a -e "${srcdir}/.git" ]; then
+                shtk_cli_error "SCM=${scm} but ${srcdir} looks" \
+                    "like a Git repo"
+            fi
+
             shtk_cli_info "Updating base source tree"
             shtk_cvs_fetch "${cvsroot}" src "$(shtk_config_get_default CVSTAG '')" \
-                "$(shtk_config_get SRCDIR)"
+                "${srcdir}"
 
             if shtk_config_has XSRCDIR; then
+                local xsrcdir="$(shtk_config_get XSRCDIR)"
+                if [ -d "${xsrcdir}" -a -e "${xsrcdir}/.git" ]; then
+                    shtk_cli_error "SCM=${scm} but ${xsrcdir} looks" \
+                        "like a Git repo"
+                fi
+
                 shtk_cli_info "Updating X11 source tree"
                 shtk_cvs_fetch "${cvsroot}" xsrc \
-                    "$(shtk_config_get_default CVSTAG '')" "$(shtk_config_get XSRCDIR)"
+                    "$(shtk_config_get_default CVSTAG '')" "${xsrcdir}"
             fi
             ;;
 
         git)
             local srcrepo="$(shtk_config_get GIT_SRC_REPO)"
             local srcbranch="$(shtk_config_get GIT_SRC_BRANCH)"
+
+            local srcdir="$(shtk_config_get SRCDIR)"
+            if [ -d "${srcdir}" -a -e "${srcdir}/CVS" ]; then
+                shtk_cli_error "SCM=${scm} but ${srcdir} looks" \
+                    "like a CVS checkout"
+            fi
+
             shtk_cli_info "Updating base source tree"
-            shtk_git_fetch "${srcrepo}" "${srcbranch}" "$(shtk_config_get SRCDIR)"
+            shtk_git_fetch "${srcrepo}" "${srcbranch}" "${srcdir}"
 
             if shtk_config_has XSRCDIR; then
+                local xsrcdir="$(shtk_config_get XSRCDIR)"
+                if [ -d "${xsrcdir}" -a -e "${xsrcdir}/CVS" ]; then
+                    shtk_cli_error "SCM=${scm} but ${xsrcdir} looks" \
+                        "like a CVS checkout"
+                fi
+
                 local xsrcrepo="$(shtk_config_get GIT_XSRC_REPO)"
                 local xsrcbranch="$(shtk_config_get GIT_XSRC_BRANCH)"
                 shtk_cli_info "Updating X11 source tree"
-                shtk_git_fetch "${xsrcrepo}" "${xsrcbranch}" "$(shtk_config_get XSRCDIR)"
+                shtk_git_fetch "${xsrcrepo}" "${xsrcbranch}" "${xsrcdir}"
             fi
             ;;
 

sysbuild_test.sh

@@ -1147,6 +1147,78 @@ EOF
 }
 
 
+shtk_unittest_add_test fetch__cvs__update__src_is_git
+fetch__cvs__update__src_is_git_test() {
+    mkdir -p checkout/src/.git
+    cat >test.conf <<EOF
+SCM=cvs
+CVSROOT=irrelevant
+SRCDIR="$(pwd)/checkout/src"
+XSRCDIR=
+EOF
+
+    cat >experr <<EOF
+sysbuild: E: SCM=cvs but $(pwd)/checkout/src looks like a Git repo
+EOF
+    assert_command -s exit:1 -o empty -e file:experr sysbuild -c test.conf fetch
+}
+
+
+shtk_unittest_add_test fetch__cvs__update__xsrc_is_git
+fetch__cvs__update__xsrc_is_git_test() {
+    mock_cvsroot=":local:$(pwd)/cvsroot"
+    create_mock_cvsroot "${mock_cvsroot}"
+    mkdir -p checkout/xsrc/.git
+    cat >test.conf <<EOF
+SCM=cvs
+CVSROOT="${mock_cvsroot}"
+SRCDIR="$(pwd)/checkout/src"
+XSRCDIR="$(pwd)/checkout/xsrc"
+EOF
+
+    assert_command -s exit:1 \
+        -o ignore \
+        -e match:"E: SCM=cvs but $(pwd)/checkout/xsrc looks like a Git repo" \
+        sysbuild -c test.conf fetch
+}
+
+
+shtk_unittest_add_test fetch__git__update__src_is_cvs
+fetch__git__update__src_is_cvs_test() {
+    mkdir -p checkout/src/CVS
+    cat >test.conf <<EOF
+SCM=git
+GIT_SRC_REPO="$(pwd)/src.git"
+SRCDIR="$(pwd)/checkout/src"
+XSRCDIR=
+EOF
+
+    cat >experr <<EOF
+sysbuild: E: SCM=git but $(pwd)/checkout/src looks like a CVS checkout
+EOF
+    assert_command -s exit:1 -o empty -e file:experr sysbuild -c test.conf fetch
+}
+
+
+shtk_unittest_add_test fetch__git__update__xsrc_is_cvs
+fetch__git__update__xsrc_is_cvs_test() {
+    create_mock_git_src "$(pwd)/src.git" trunk
+    mkdir -p checkout/xsrc/CVS
+    cat >test.conf <<EOF
+SCM=git
+GIT_SRC_REPO="$(pwd)/src.git"
+GIT_XSRC_REPO=irrelevant
+SRCDIR="$(pwd)/checkout/src"
+XSRCDIR="$(pwd)/checkout/xsrc"
+EOF
+
+    assert_command -s exit:1 \
+        -o ignore \
+        -e match:"E: SCM=git but $(pwd)/checkout/xsrc looks like a CVS checkout" \
+        sysbuild -c test.conf fetch
+}
+
+
 shtk_unittest_add_test fetch__git__checkout__src_only
 fetch__git__checkout__src_only_test() {
     create_mock_git_src "$(pwd)/src.git" trunk