Add conformance testing to string.format implementation (#293)

Apologies for the large PR. The logical way to split this up is for
`Format.java` to be its own PR with everything else separate but it may
just be easier to review this all at once. So, an easy way to review is:
* `Format.java` for all the formatting fixes
*  Everything else that runs the conformance tests

This adds conformance testing to our implementation of `string.format`.
cel-java does not currently provide a `string.format` function so we
implement our own and add it to the protovalidate-java CEL runtime.

While formatting is not (yet) a part of the cel-spec, they do provide
conformance test data for validating behavior. So, to ensure we are
conformant, we use this test data and run it against our implementation.

See the test data
[here](https://github.com/google/cel-spec/blob/master/tests/simple/testdata/string_ext.textproto).
Note that this file contains various sections for testing. However, we
are only concerned with the `format` and `format_errors` sections. In
addition, since we are only testing for formatting, we do not handle
every `oneof` case or variation in the `SimpleTest` definition -- only
expected results or evaluation errors. If others are added down the road
in future versions of the spec, we can adjust these tests.

There are few tests marked as skipped in `FormatTest` as these seem to
be related to issues in cel-java's runtime (or in how we set up our
environment) because the same issues happen when trying to use those
expressions in protovalidate-java. Probably worth investigating or
filing an issue for cel-java, but didn't want to hold up this PR.

Author: smaye81

build.gradle.kts

@@ -90,8 +90,66 @@ tasks.register<Exec>("generateTestSourcesNoImports") {
     commandLine(buf.asPath, "generate", "--template", "src/test/resources/proto/buf.gen.noimports.yaml")
 }
 
+tasks.register<Exec>("generateCelConformance") {
+    dependsOn("generateCelConformanceTestTypes")
+    description = "Generates CEL conformance code with buf generate for unit tests."
+    commandLine(
+        buf.asPath,
+        "generate",
+        "--template",
+        "src/test/resources/proto/buf.gen.cel.yaml",
+        "buf.build/google/cel-spec:${project.findProperty("cel.spec.version")}",
+        "--exclude-path",
+        "cel/expr/conformance/proto2",
+        "--exclude-path",
+        "cel/expr/conformance/proto3",
+    )
+}
+
+// The conformance tests use the Protobuf package path for tests that use these types.
+// i.e. cel.expr.conformance.proto3.TestAllTypes. But, if we use managed mode it adds 'com'
+// to the prefix. Additionally, we can't disable managed mode because the java_package option
+// specified in these proto files is "dev.cel.expr.conformance.proto3". So, to get around this,
+// we're generating these separately and specifying a java_package override of the package we need.
+tasks.register<Exec>("generateCelConformanceTestTypes") {
+    dependsOn("exportProtovalidateModule")
+    description = "Generates CEL conformance test types with buf generate for unit tests using a Java package override."
+    commandLine(
+        buf.asPath,
+        "generate",
+        "--template",
+        "src/test/resources/proto/buf.gen.cel.testtypes.yaml",
+        "buf.build/google/cel-spec:${project.findProperty("cel.spec.version")}",
+        "--path",
+        "cel/expr/conformance/proto3",
+    )
+}
+
+var getCelTestData =
+    tasks.register<Exec>("getCelTestData") {
+        val celVersion = project.findProperty("cel.spec.version")
+        val fileUrl = "https://raw.githubusercontent.com/google/cel-spec/refs/tags/$celVersion/tests/simple/testdata/string_ext.textproto"
+        val targetDir = File("${project.projectDir}/src/test/resources/testdata")
+        val file = File(targetDir, "string_ext_$celVersion.textproto")
+
+        onlyIf {
+            // Only run curl if file doesn't exist
+            !file.exists()
+        }
+        doFirst {
+            file.parentFile.mkdirs()
+            commandLine(
+                "curl",
+                "-fsSL",
+                "-o",
+                file.absolutePath,
+                fileUrl,
+            )
+        }
+    }
+
 tasks.register("generateTestSources") {
-    dependsOn("generateTestSourcesImports", "generateTestSourcesNoImports")
+    dependsOn("generateTestSourcesImports", "generateTestSourcesNoImports", "generateCelConformance")
     description = "Generates code with buf generate for unit tests"
 }
 
@@ -206,6 +264,7 @@ allprojects {
         }
     }
     tasks.withType<Test>().configureEach {
+        dependsOn(getCelTestData)
         useJUnitPlatform()
         this.testLogging {
             events("failed")

gradle.properties

@@ -6,3 +6,6 @@ protovalidate.conformance.args = --strict_message --strict_error --expected_fail
 
 # Argument to the license-header CLI
 license-header.years = 2023-2024
+
+# Version of the cel-spec that this implementation is conformant with
+cel.spec.version = v0.24.0