ci: add pure `-os android` checks (#14837)

.github/workflows/android_cross_compile.vsh

@@ -0,0 +1,67 @@
+#!/usr/bin/env -S v
+
+module main
+
+import os
+import vab.vxt
+import vab.android.ndk
+
+fn main() {
+	assert ndk.found()
+	assert vxt.found()
+
+	work_dir := os.join_path(os.temp_dir(), 'android_cross_compile_test')
+	os.rm(work_dir) or {}
+	os.mkdir_all(work_dir) or { panic(err) }
+	vexe := vxt.vexe()
+
+	examples_dir := os.join_path(vxt.home(), 'examples')
+	v_example := os.join_path(examples_dir, 'toml.v')
+
+	ndk_version := ndk.default_version()
+
+	sysroot_path := ndk.sysroot_path(ndk_version) or { panic(err) }
+	include_path := os.join_path(sysroot_path, 'usr', 'include')
+	android_include_path := os.join_path(include_path, 'android')
+
+	//'-I"$include_path"'
+	cflags := ['-I"$android_include_path"', '-Wno-unused-value', '-Wno-implicit-function-declaration',
+		'-Wno-int-conversion']
+	for arch in ndk.supported_archs {
+		for level in ['min', 'max'] {
+			compiler_api := match level {
+				'min' {
+					ndk.compiler_min_api(.c, ndk_version, arch) or { panic(err) }
+				}
+				'max' {
+					ndk.compiler_max_api(.c, ndk_version, arch) or { panic(err) }
+				}
+				else {
+					panic('invalid min/max level')
+				}
+			}
+
+			os.setenv('VCROSS_COMPILER_NAME', compiler_api, true)
+			c_file := os.join_path(work_dir, arch + '-' + level + '.c')
+			o_file := os.join_path(work_dir, arch + '-' + level + '.o')
+
+			// x.v -> x.c
+			v_compile_cmd := '$vexe -o $c_file -os android -gc none $v_example'
+			vres := os.execute(v_compile_cmd)
+			if vres.exit_code != 0 {
+				panic('"$v_compile_cmd" failed: $vres.output')
+			}
+			assert os.exists(c_file)
+
+			// x.c -> x.o
+			compile_cmd := '$compiler_api ${cflags.join(' ')} -c $c_file -o $o_file'
+			cres := os.execute(compile_cmd)
+			if cres.exit_code != 0 {
+				panic('"$compile_cmd" failed: $cres.output')
+			}
+			assert os.exists(o_file)
+			compiler_exe_name := os.file_name(compiler_api)
+			println('Compiled examples/toml.v successfully for ($level) $arch $compiler_exe_name')
+		}
+	}
+}

.github/workflows/vab_ci.yml

@@ -48,3 +48,27 @@ jobs:
           safe_name=$(echo "$example" | sed 's%/%-%' | sed 's%\.%-%' )
           vab examples/$example -o apks/$safe_name.apk
         done
+
+  v-compiles-os-android:
+    runs-on: ubuntu-20.04
+    if: github.event_name != 'push' || github.event.ref == 'refs/heads/master' || github.event.repository.full_name != 'vlang/v'
+    timeout-minutes: 10
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build V
+      run: make && sudo ./v symlink
+
+    - name: Install vab
+      run: |
+        v install vab
+        v -g ~/.vmodules/vab
+        sudo ln -s ~/.vmodules/vab/vab /usr/local/bin/vab
+
+    - name: Run vab --help
+      run: vab --help
+
+    - name: Run vab doctor
+      run: vab doctor
+
+    - name: Check `v -os android` *without* -apk flag
+      run: .github/workflows/android_cross_compile.vsh

vlib/os/os_android.c.v

@@ -1,5 +1,8 @@
 module os
 
+#include <asset_manager.h>
+#include <asset_manager_jni.h>
+
 pub enum AssetMode {
 	buffer = C.AASSET_MODE_BUFFER // Caller plans to ask for a read-only buffer with all data.
 	random = C.AASSET_MODE_RANDOM // Read chunks, and seek forward and backward.