fix: Update readme with correct path to example policy (#312)

Also add test to lock down example policy path.
Also Fix clippy warning by using unwrap_or_default

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

.github/workflows/pr.yml

@@ -30,6 +30,8 @@ jobs:
       run: cargo test -r --doc
     - name: Run tests
       run: cargo test -r
+    - name: Run example
+      run: cargo run --example regorus -- eval -d examples/server/allowed_server.rego -i examples/server/input.json data.example
     - name: Run tests (ACI)
       run: cargo test -r --test aci
     - name: Run tests (KATA)

README.md

@@ -184,11 +184,11 @@ This produces the following output
 }
 ```
 
-Next, evaluate a sample [policy](https://github.com/microsoft/regorus/blob/main/examples/example.rego) and [input](https://github.com/microsoft/regorus/blob/main/examples/input.json)
+Next, evaluate a sample [policy](https://github.com/microsoft/regorus/blob/main/examples/server/allowed_server.rego) and [input](https://github.com/microsoft/regorus/blob/main/examples/server/input.json)
 (borrowed from [Rego tutorial](https://www.openpolicyagent.org/docs/latest/#2-try-opa-eval)):
 
 ```bash
-$ regorus eval -d examples/example.rego -i examples/input.json data.example
+$ regorus eval -d examples/server/allowed_server.rego -i examples/server/input.json data.example
 ```
 
 Finally, evaluate real-world [policies](tests/aci/) used in Azure Container Instances (ACI)
@@ -204,7 +204,7 @@ Regorus allows determining which lines of a policy have been executed using the
 We can try it out using the `regorus` example program by passing in the `--coverage` flag.
 
 ```shell
-$ regorus eval -d examples/example.rego -i examples/input.json data.example --coverage
+$ regorus eval -d examples/server/allowed_server.rego -i examples/server/input.json data.example --coverage
 ```
 
 It produces the following coverage report which shows that all lines are executed except the line that sets `allow` to true.

src/utils.rs

@@ -78,10 +78,7 @@ pub fn get_extra_arg(
     module: Option<&str>,
     functions: &FunctionTable,
 ) -> Option<Ref<Expr>> {
-    match get_extra_arg_impl(expr, module, functions) {
-        Ok(a) => a,
-        _ => None,
-    }
+    get_extra_arg_impl(expr, module, functions).unwrap_or_default()
 }
 
 pub fn gather_functions(modules: &[Ref<Module>]) -> Result<FunctionTable> {