Support marking variables as readonly

When the magic variable .KATI_READONLY is set to a variable name, any
further attempts to modify the named variable will result in an error.

  FOO := bar
  .KATI_READONLY := FOO
  FOO := baz  # Error!

This is useful to make some global configuration readonly so that
another makefile cannot change it. In Android, we emulated this by
backing up some global configuration before including the Android.mk
files, then comparing the current values to the backed up values after
they've been included. But this means we don't know the location that
modified the variable, just that something did. And it's not perfect,
since the backup can also be changed.

Something similar to this could be implemented with `override`, but then
setting the variable silently fails, and it still could be overriden
with another override.

4 files changed, 159 insertions, 0 deletions

diff --git a/testcase/readonly_global.sh b/testcase/readonly_global.sh
new file mode 100644
index 0000000..33695f2
--- /dev/null
+++ b/testcase/readonly_global.sh
@@ -0,0 +1,47 @@
+#!/bin/bash
+#
+# Copyright 2016 Google Inc. All rights reserved
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http:#www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -u
+
+mk="$@"
+
+function build() {
+  cat <<EOF > Makefile
+FOO $1 bar
+.KATI_READONLY $2 FOO
+FOO $3 baz
+all:
+EOF
+
+  echo "Testcase: $1 $2 $3"
+  if echo "${mk}" | grep -q "^make"; then
+    # Make doesn't support .KATI_READONLY
+    echo "Makefile:3: *** cannot assign to readonly variable: FOO"
+  else
+    ${mk} 2>&1 && echo "Clean exit"
+  fi
+}
+
+build "=" "=" "="
+build "=" "+=" "="
+build "=" ":=" "="
+
+build "=" ":=" ":="
+build "=" ":=" "+="
+
+build ":=" ":=" ":="
+build ":=" ":=" "+="
+build ":=" ":=" "="
diff --git a/testcase/readonly_global_missing.sh b/testcase/readonly_global_missing.sh
new file mode 100644
index 0000000..cab86f2
--- /dev/null
+++ b/testcase/readonly_global_missing.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+#
+# Copyright 2016 Google Inc. All rights reserved
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http:#www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -u
+
+mk="$@"
+
+cat <<EOF > Makefile
+all: FOO = bar
+.KATI_READONLY = FOO
+all:
+EOF
+
+if echo "${mk}" | grep -q "^make"; then
+  # Make doesn't support .KATI_READONLY
+  echo "Makefile:2: *** unknown variable: FOO"
+else
+  ${mk} 2>&1 && echo "Clean exit"
+fi
diff --git a/testcase/readonly_rule.sh b/testcase/readonly_rule.sh
new file mode 100644
index 0000000..676d639
--- /dev/null
+++ b/testcase/readonly_rule.sh
@@ -0,0 +1,48 @@
+#!/bin/bash
+#
+# Copyright 2016 Google Inc. All rights reserved
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http:#www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -u
+
+mk="$@"
+
+function build() {
+  cat <<EOF > Makefile
+all: FOO $1 bar
+all: .KATI_READONLY $2 FOO
+FOO $3 foo
+all: FOO $3 baz
+all:
+EOF
+
+  echo "Testcase: $1 $2 $3"
+  if echo "${mk}" | grep -q "^make"; then
+    # Make doesn't support .KATI_READONLY
+    echo "Makefile:4: *** cannot assign to readonly variable: FOO"
+  else
+    ${mk} 2>&1 && echo "Clean exit"
+  fi
+}
+
+#build "=" "=" "="
+#build "=" "+=" "="
+#build "=" ":=" "="
+#
+#build "=" ":=" ":="
+#build "=" ":=" "+="
+#
+#build ":=" ":=" ":="
+build ":=" ":=" "+="
+#build ":=" ":=" "="
diff --git a/testcase/readonly_rule_missing.sh b/testcase/readonly_rule_missing.sh
new file mode 100644
index 0000000..6940438
--- /dev/null
+++ b/testcase/readonly_rule_missing.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+#
+# Copyright 2016 Google Inc. All rights reserved
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http:#www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -u
+
+mk="$@"
+
+cat <<EOF > Makefile
+FOO = bar
+all: .KATI_READONLY = FOO
+all:
+EOF
+
+if echo "${mk}" | grep -q "^make"; then
+  # Make doesn't support .KATI_READONLY
+  echo "Makefile:2: *** unknown variable: FOO"
+else
+  ${mk} 2>&1 && echo "Clean exit"
+fi