feat: Show non-fatal stanc warnings

Show non-fatal stanc warning messages to user.
Exposes information available since httpstan 2.2.0.

Closes #144

pyproject.toml

@@ -23,7 +23,7 @@ classifiers = [
 [tool.poetry.dependencies]
 python = "^3.7"
 aiohttp = "^3.6"
-httpstan = "^2.1.0"
+httpstan = "^2.2.0"
 numpy = "^1.7"
 clikit = "^0.6.2"
 

stan/model.py

@@ -271,10 +271,13 @@ async def go():
             # Note: during compilation `httpstan` redirects stderr to /dev/null, making `print` impossible.
             path, payload = "/v1/models", {"program_code": program_code}
             async with aiohttp.request("POST", f"http://{host}:{port}{path}", json=payload) as resp:
+                response_payload = await resp.json()
                 if resp.status != 201:
-                    raise RuntimeError((await resp.json())["message"])
-                assert model_name == (await resp.json())["name"]
-
+                    raise RuntimeError(response_payload["message"])
+                assert model_name == response_payload["name"]
+                if response_payload.get("stanc_warnings"):
+                    io.error_line("<comment>Warnings from stanc:</comment>")
+                    io.error_line(response_payload["stanc_warnings"])
             path, payload = f"/v1/{model_name}/params", {"data": data}
             async with aiohttp.request("POST", f"http://{host}:{port}{path}", json=payload) as resp:
                 if resp.status != 200:

tests/test_stanc_warnings.py

@@ -0,0 +1,33 @@
+"""Test that stanc warnings are visible."""
+import contextlib
+import io
+
+import stan
+
+
+def test_stanc_no_warning() -> None:
+    """No warnings."""
+    program_code = "parameters {real y;} model {y ~ normal(0,1);}"
+    buffer = io.StringIO()
+    with contextlib.redirect_stderr(buffer):
+        stan.build(program_code=program_code)
+    assert "warning" not in buffer.getvalue().lower()
+
+
+def test_stanc_warning() -> None:
+    """Test that stanc warning is shown to user."""
+    # stanc prints warning:
+    # assignment operator <- is deprecated in the Stan language; use = instead.
+    program_code = """
+    parameters {
+    real y;
+    }
+    model {
+    real x;
+    x <- 5;
+    }
+    """
+    buffer = io.StringIO()
+    with contextlib.redirect_stderr(buffer):
+        stan.build(program_code=program_code)
+    assert "assignment operator <- is deprecated in the Stan language" in buffer.getvalue()