[lit] Allow passing extra commands to executeShTest

This allows creating custom test formats on top of `executeShTest` that
inject commands at the beginning of the file being parsed, without
requiring these commands to physically appear in the test file itself.

For example, one could define a test format that prints out additional
debug information at the beginning of each test. More realistically,
this has been used to define custom test formats like one that supports
compilation failure tests (e.g. with the extension `compile.fail.cpp`)
by injecting a command that calls the compiler on the file itself and
expects it to fail.

Without this change, the only alternative is to create a temporary file
with the same content as the original test, then prepend the desired
`// RUN:` lines to that file, and call `executeShTest` on that file
instead. This is both slow and cumbersome to do.

Differential Revision: https://reviews.llvm.org/D76290

llvm/utils/lit/lit/TestRunner.py

@@ -1488,13 +1488,17 @@ def _runShTest(test, litConfig, useExternalSh, script, tmpBase):
 
 
 def executeShTest(test, litConfig, useExternalSh,
-                  extra_substitutions=[]):
+                  extra_substitutions=[],
+                  preamble_commands=[]):
     if test.config.unsupported:
         return lit.Test.Result(Test.UNSUPPORTED, 'Test is unsupported')
 
-    script = parseIntegratedTestScript(test)
-    if isinstance(script, lit.Test.Result):
-        return script
+    script = list(preamble_commands)
+    parsed = parseIntegratedTestScript(test, require_script=not script)
+    if isinstance(parsed, lit.Test.Result):
+        return parsed
+    script += parsed
+
     if litConfig.noExecute:
         return lit.Test.Result(Test.PASS)
 

llvm/utils/lit/tests/Inputs/shtest-inject/lit.cfg

@@ -0,0 +1,17 @@
+import lit
+
+class CustomFormat(lit.formats.TestFormat):
+    def execute(self, test, litConfig):
+        commands = [
+            'echo "THIS WAS"',
+            'echo "INJECTED"'
+        ]
+        return lit.TestRunner.executeShTest(test, litConfig,
+                                            useExternalSh=False,
+                                            preamble_commands=commands)
+
+config.name = 'shtest-inject'
+config.suffixes = ['.txt']
+config.test_format = CustomFormat()
+config.test_source_root = None
+config.test_exec_root = None

llvm/utils/lit/tests/Inputs/shtest-inject/test-empty.txt

@@ -0,0 +1,3 @@
+
+# This test voluntarily has no RUN lines or anything else. The RUN lines are
+# injected by the test format.

llvm/utils/lit/tests/Inputs/shtest-inject/test-many.txt

@@ -0,0 +1,7 @@
+
+# This test has several RUN lines, but more run lines are prepended to it by
+# the test format in use.
+
+# RUN: echo "IN THE FILE"
+# RUN: echo "IF IT WORKS"
+# RUN: echo "AS EXPECTED"

llvm/utils/lit/tests/Inputs/shtest-inject/test-one.txt

@@ -0,0 +1,5 @@
+
+# This test has one RUN line, but more run lines are prepended to it by the
+# test format in use.
+
+# RUN: echo "IN THE FILE"

llvm/utils/lit/tests/shtest-inject.py

@@ -0,0 +1,49 @@
+# Check that we can inject commands at the beginning of a ShTest using a custom
+# test format.
+
+# RUN: %{lit} -j 1 %{inputs}/shtest-inject/test-empty.txt --show-all | FileCheck --check-prefix=CHECK-TEST1 %s
+#
+# CHECK-TEST1: Script:
+# CHECK-TEST1: --
+# CHECK-TEST1: echo "THIS WAS"
+# CHECK-TEST1: echo "INJECTED"
+# CHECK-TEST1: --
+#
+# CHECK-TEST1: THIS WAS
+# CHECK-TEST1: INJECTED
+#
+# CHECK-TEST1: Expected Passes    : 1
+
+# RUN: %{lit} -j 1 %{inputs}/shtest-inject/test-one.txt --show-all | FileCheck --check-prefix=CHECK-TEST2 %s
+#
+# CHECK-TEST2: Script:
+# CHECK-TEST2: --
+# CHECK-TEST2: echo "THIS WAS"
+# CHECK-TEST2: echo "INJECTED"
+# CHECK-TEST2: echo "IN THE FILE"
+# CHECK-TEST2: --
+#
+# CHECK-TEST2: THIS WAS
+# CHECK-TEST2: INJECTED
+# CHECK-TEST2: IN THE FILE
+#
+# CHECK-TEST2: Expected Passes    : 1
+
+# RUN: %{lit} -j 1 %{inputs}/shtest-inject/test-many.txt --show-all | FileCheck --check-prefix=CHECK-TEST3 %s
+#
+# CHECK-TEST3: Script:
+# CHECK-TEST3: --
+# CHECK-TEST3: echo "THIS WAS"
+# CHECK-TEST3: echo "INJECTED"
+# CHECK-TEST3: echo "IN THE FILE"
+# CHECK-TEST3: echo "IF IT WORKS"
+# CHECK-TEST3: echo "AS EXPECTED"
+# CHECK-TEST3: --
+#
+# CHECK-TEST3: THIS WAS
+# CHECK-TEST3: INJECTED
+# CHECK-TEST3: IN THE FILE
+# CHECK-TEST3: IF IT WORKS
+# CHECK-TEST3: AS EXPECTED
+#
+# CHECK-TEST3: Expected Passes    : 1