fix(rust): Use an env var to control rustdoc selectively only when bu…

…ilding docs, not running doc tests

earthly/rust/scripts/std_build.py

@@ -94,8 +94,11 @@ def cargo_bench(flags: str, verbose: bool = False) -> exec_manager.Result:
 
 
 def cargo_doc(verbose: bool = False) -> exec_manager.Result:
+    # Add RUSTDOCFLAGS to the inherited environment so we can build an index page with nightly.
+    env = os.environ
+    env["RUSTDOCFLAGS"] = "-Z unstable-options --enable-index-page"
     return exec_manager.cli_run(
-        "cargo +nightly docs -Z unstable-options --enable-index-page", 
+        "cargo +nightly docs", 
         name="Documentation build", 
         verbose=verbose
     )

utilities/scripts/python/exec_manager.py

@@ -150,6 +150,7 @@ def cli_run(
     log: bool = True,
     timeout=None,
     verbose=False,
+    env=None
 ) -> Result:
     def procedure() -> ProcedureResult:
         result = subprocess.run(
@@ -159,6 +160,7 @@ def procedure() -> ProcedureResult:
             stderr=subprocess.STDOUT,
             text=True,
             timeout=timeout,
+            env=env
         )
         return ProcedureResult(result.returncode, command, result.stdout)