Check NDK version in Bazel

BUILDING.md

@@ -74,17 +74,20 @@ To fetch the required packages, using a console type:
 
 ```
 cd <sdk-path>
-tools\bin\sdkmanager.bat "platforms;android-26" "build-tools;29.0.2" ndk-bundle
+tools\bin\sdkmanager.bat "platforms;android-26" "build-tools;29.0.2"
 ```
 
-Note: this will install the latest NDK in `<sdk-path>\ndk-bundle`. The recommended version of the NDK is **r21**.
-
 If you do not have adb installed you can do so with:
 ```
 cd <sdk-path>
 tools\bin\sdkmanager.bat platform-tools
 ```
 
+Unzip the
+[Android NDK **r21**](https://dl.google.com/android/repository/android-ndk-r21-windows-x86_64.zip)
+into a directory of your choosing, and set the `ANDROID_NDK_HOME` environment
+variable to point to this directory.
+
 ### Configure the environment
 
 Either do this globally or in your shell every time.
@@ -132,17 +135,24 @@ To fetch the required packages, using a console type:
 
 ```
 cd <sdk-path>
-tools/bin/sdkmanager "platforms;android-26" "build-tools;29.0.2" ndk-bundle
+tools/bin/sdkmanager "platforms;android-26" "build-tools;29.0.2"
 ```
 
-Note: this will install the latest NDK in `<sdk-path>/ndk-bundle`. The recommended version of the NDK is **r21**.
-
 If you do not have adb installed you can do so with:
 ```
 cd <sdk-path>
 tools/bin/sdkmanager platform-tools
 ```
 
+Unzip the
+[Android NDK **r21**](https://dl.google.com/android/repository/android-ndk-r21-darwin-x86_64.zip)
+into a directory of your choosing, and set the `ANDROID_NDK_HOME` environment
+variable to point to this directory:
+
+```
+export ANDROID_NDK_HOME=<ndk-path>
+```
+
 ### Install the XCode command line tools
 
 After installing, ensure the XCode license is signed with:
@@ -199,17 +209,24 @@ To fetch the required packages, using a console type:
 
 ```
 cd <sdk-path>
-tools/bin/sdkmanager "platforms;android-26" "build-tools;29.0.2" ndk-bundle
+tools/bin/sdkmanager "platforms;android-26" "build-tools;29.0.2"
 ```
 
-Note: this will install the latest NDK in `<sdk-path>/ndk-bundle`. The recommended version of the NDK is **r21**.
-
 If you do not have adb installed you can do so with:
 ```
 cd <sdk-path>
 tools/bin/sdkmanager platform-tools
 ```
 
+Unzip the
+[Android NDK **r21**](https://dl.google.com/android/repository/android-ndk-r21-linux-x86_64.zip)
+into a directory of your choosing, and set the `ANDROID_NDK_HOME` environment
+variable to point to this directory:
+
+```
+export ANDROID_NDK_HOME=<ndk-path>
+```
+
 ### Install other libraries
 
 ```

gapidapk/android/apk/rules.bzl

@@ -124,6 +124,7 @@ def gapid_apk(name = "", abi = "", pkg = "", libs = {}, bins = {}):
         assets = assets,
         assets_dir = abi,
         deps = [
+            "@ndk_version_check//:version_check",
             "//gapidapk/android/app/src/main:gapid",
             ":" + name + "_native",
         ],

tools/build/rules/android.bzl

@@ -135,3 +135,51 @@ ndk_vk_validation_layer = repository_rule(
         "ANDROID_NDK_HOME",
     ],
 )
+
+# Enforce NDK version by checking $ANDROID_NDK_HOME/source.properties
+def _ndk_version_check(repository_ctx):
+    # This should be updated in sync with BUILDING.md documentation
+    expectedVersion = "21.0.6113669"
+
+    # Extract NDK version string from $ANDROID_NDK_HOME/source.properties,
+    # which has the following format:
+    #   Pkg.Desc = Android NDK
+    #   Pkg.Revision = 21.0.6113669
+    sourcePropFile = repository_ctx.os.environ["ANDROID_NDK_HOME"] + "/source.properties"
+    sourceProp = repository_ctx.read(sourcePropFile)
+    secondLine = sourceProp.split("\n")[1]
+    ndkVersion = secondLine.split(" ")[2]
+
+    # We want to fail only when Bazel tries to actually build a native target
+    # on Android, such that e.g. the presubmit check can pass without having
+    # to install the expected NDK version. To this aim, we create a rule to be
+    # used as a dependency in android_binary() rules. This rule fails when our
+    # check fails, and otherwise returns a CcInfo provider needed to be a
+    # valid dependency of android_binary().
+    ruleBody = "def _version_check(ctx):\n"
+    if ndkVersion != expectedVersion:
+        ruleBody += "    fail(\"Wrong NDK version: expected " + expectedVersion + ", got " + ndkVersion + "\")\n"
+    else:
+        ruleBody += "    return [CcInfo()]\n"
+    ruleBody += "\n"
+    ruleBody += "version_check = rule(implementation = _version_check)\n"
+    repository_ctx.file("version.bzl", ruleBody)
+
+    # Create a BUILD file to instanciate the rule.
+    build = """
+load("//:version.bzl", "version_check")
+
+version_check(
+    name = "version_check",
+    visibility = ["//visibility:public"],
+)
+"""
+    repository_ctx.file("BUILD", build)
+
+ndk_version_check = repository_rule(
+    implementation = _ndk_version_check,
+    local = True,
+    environ = [
+        "ANDROID_NDK_HOME",
+    ]
+)

tools/build/workspace.bzl

@@ -16,7 +16,7 @@
 # dependencies and toolchains.
 
 load("@gapid//tools/build:cc_toolchain.bzl", "cc_configure")
-load("@gapid//tools/build/rules:android.bzl", "android_native_app_glue", "ndk_vk_validation_layer")
+load("@gapid//tools/build/rules:android.bzl", "android_native_app_glue", "ndk_vk_validation_layer", "ndk_version_check")
 load("@gapid//tools/build/rules:repository.bzl", "github_repository", "maybe_repository")
 load("@gapid//tools/build/third_party:breakpad.bzl", "breakpad")
 load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository", "new_git_repository")
@@ -324,6 +324,12 @@ def gapid_dependencies(android = True, mingw = True, locals = {}):
             locals = locals,
         )
 
+        maybe_repository(
+            ndk_version_check,
+            name = "ndk_version_check",
+            locals = locals,
+        )
+
         # Use the LLVM libc++ Android toolchain.
         native.bind(
             name = "android/crosstool",