rust: Fix daylight saving inaccuracy

src/shacl2code/lang/templates/rust/Cargo.toml.j2

@@ -8,7 +8,7 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-chrono = { version = "0.4", features = ["serde"] }
+chrono = { version = "0.4.31", features = ["serde"] }
 lazy_static = "1.4"
 regex = "1"
 serde = { version = "1", features = ["derive"] }

src/shacl2code/lang/templates/rust/lib.rs.j2

@@ -226,9 +226,9 @@ fn decode_datetime_string(
         "" => {
             let naive = NaiveDateTime::parse_from_str(base, "%Y-%m-%dT%H:%M:%S")
                 .map_err(|e| Error::Decode(path.to_string(), format!("Invalid date time '{}': {}", s, e)))?;
-            let local_offset = *Local::now().offset();
-            Ok(local_offset.from_local_datetime(&naive).single()
-                .ok_or_else(|| Error::Decode(path.to_string(), format!("Ambiguous local time '{}'", s)))?)
+            Ok(Local.from_local_datetime(&naive).single()
+                .ok_or_else(|| Error::Decode(path.to_string(), format!("Ambiguous local time '{}'", s)))?
+                .fixed_offset())
         }
         _ => {
             let full = format!("{}{}", base, tz);

tests/test_rust.py

@@ -10,6 +10,7 @@
 import textwrap
 from enum import Enum
 from pathlib import Path
+from typing import Callable, Optional
 
 import pytest
 
@@ -117,7 +118,7 @@ def f(code_fragment, *, passes=True, progress=None):
                 [dependencies]
                 shacl_model = {{ path = "{test_lib}" }}
                 serde_json = "1"
-                chrono = {{ version = "0.4", features = ["serde"] }}
+                chrono = {{ version = "0.4.31", features = ["serde"] }}
                 """))
 
         src = tmp_path / "src" / "main.rs"
@@ -643,6 +644,32 @@ def test_datetime_decode(compile_test, value, expect):
         ), f"Test failed. Expected {s!r}, got {output.rstrip()!r}"
 
 
+def test_datetime_decode_dst_transition(
+    compile_test: Callable[..., Optional[str]], monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """Offset must reflect the daylight saving time (DST) rule of the
+    parsed date, not of "now"."""
+    monkeypatch.setenv("TZ", "America/New_York")
+
+    # Winter and summer require different offsets, so both must be resolved per-date, not from "now".
+    output = compile_test(
+        """\
+        let path = Path::new();
+
+        let winter = decode_date_time("2024-01-15T12:00:00", &path)?;
+        println!("{}", encode_date_time(&winter));
+
+        let summer = decode_date_time("2024-07-15T12:00:00", &path)?;
+        println!("{}", encode_date_time(&summer));
+        """,
+    )
+    assert output is not None
+
+    lines = output.splitlines()
+    assert lines[0] == "2024-01-15T12:00:00-05:00", "EST (no DST) offset expected"
+    assert lines[1] == "2024-07-15T12:00:00-04:00", "EDT (DST) offset expected"
+
+
 @timetests.datetimestamp_decode_tests()
 def test_datetimestamp_decode(compile_test, value, expect):
     output = compile_test(
@@ -724,7 +751,7 @@ def test_extensible_context(compile_test, roundtrip):
 
 
 class _Prop:
-    def __init__(self, path, varname=None):
+    def __init__(self, path: str, varname: Optional[str] = None) -> None:
         self.path = path
         self.varname = varname if varname is not None else path