[Fortran] Respect NO_STOP_MESSAGE if it is set in the environment

Fortran/README.md

@@ -0,0 +1,58 @@
+# Fortran Tests
+
+This directory contains test suites such as those of
+[gfortran](https://github.com/llvm/llvm-test-suite/tree/main/Fortran/gfortran)
+and [NIST](https://github.com/llvm/llvm-test-suite/tree/main/Fortran/UnitTests/fcvs21_f95),
+end-to-end tests of functions with runtime support as well as some proxy
+applications such as
+[SNAP](https://github.com/llvm/llvm-test-suite/tree/main/Fortran/SNAP).
+When the test suite is configured with `-DTEST_SUITE_SUBDIRS=Fortran`, in most
+cases, all tests in this directory will be run. The exception is where certain
+tests/test-suites are disabled on certain platforms. For instance, the gfortran
+tests are not run on RISC-V.
+
+## Setting NO_STOP_MESSAGE in the environment
+
+By default, flang prints a stop message in certain circumstances, typically
+when the `STOP` statement is executed. This breaks the NIST tests. Setting
+`NO_STOP_MESSAGE=1` in the environment disables this behavior. If
+`NO_STOP_MESSAGE` is not set in the environment when running the tests, it will
+be set automatically. See
+[Fortran/lit.local.cfg](https://github.com/llvm/llvm-test-suite/tree/main/Fortran/lit.local.cfg)
+for details.
+
+If adding a subdirectory with tests that need to check the `STOP` message,
+add a `lit.local.cfg` file in that subdirectory with code to unset the
+variable. For instance, something like this
+
+```python
+config["NO_STOP_MESSAGE"] = ""
+```
+
+## Building and running a specific test suite
+
+It is possible to configure the llvm-test-suite to run only a subset of the
+tests here. This can be done by specifying an appropriate subdirectory of
+`Fortran/`. For instance, to build and run only the gfortran tests, the add
+the following when running cmake:
+
+```
+-DTEST_SUITE_SUBDIRS=Fortran/gfortran
+```
+
+Keep in mind that when doing so the `lit.local.cfg` files from any parent
+directories will not be processed. This may result in test failures if the tests
+expect certain configuration options to have been set, and those are only set
+in the `lit.local.cfg` file in a parent directory.
+
+This case can be seen when one attempts to run only the NIST tests by setting
+`-DTEST_SUITE_SUBDIRS=Fortran/UnitTests/fcvs21_f95`. Since
+[Fortran/lit.local.cfg](https://github.com/llvm/llvm-test-suite/tree/main/Fortran/lit.local.cfg)
+will not be processed in this case, `NO_STOP_MESSAGE=1` will not be added to
+the environment automatically and several tests will fail. In this case,
+`NO_STOP_MESSAGE=1` must be set explicitly when running the tests. One way of
+doing this is shown below.
+
+```shell
+NO_STOP_MESSAGE=1 /path/to/llvm-lit -s .
+```

Fortran/lit.local.cfg

@@ -1,4 +1,7 @@
 # Flang uses NO_STOP_MESSAGE to control the output of the STOP statement.
 # We should set it for running the tests, otherwise they might choke on warnings
-# about signaling INEXACT exceptions.
-config.environment["NO_STOP_MESSAGE"] = "1"
+# about signaling INEXACT exceptions. If NO_STOP_MESSAGE was set in the
+# environment, that value will have been added to the config in
+# llvm-test-suite/lit.cfg and should not be overridden.
+if "NO_STOP_MESSAGE" not in config.environment:
+  config.environment["NO_STOP_MESSAGE"] = "1"

lit.cfg

@@ -25,6 +25,8 @@ config.traditional_output = False
 config.single_source = False
 if "SSH_AUTH_SOCK" in os.environ:
     config.environment["SSH_AUTH_SOCK"] = os.environ["SSH_AUTH_SOCK"]
+if "NO_STOP_MESSAGE" in os.environ:
+   config.environment["NO_STOP_MESSAGE"] = os.environ["NO_STOP_MESSAGE"]
 
 # Load previous test results so we can skip tests that did not change.
 previous_results_file = lit_config.params.get("previous", None)