[llvm-cov][test] Add test coverage for "gcov" implying "llvm-cov gcov" compatibility.

[rupprecht]

Summary

Much like other LLVM binary utilities, llvm-cov has a symlink compatibility feature where it runs in gcov compatibility mode if the binary name ends in gcov. This is identical to invoking llvm-cov gcov ....

[MaskRay]

Thanks!

[jhenderson]

Is it strictly ends with, or do things like file extensions, version numbers etc have an impact? See the additional test cases in https://github.com/llvm/llvm-project/blob/main/llvm/test/tools/llvm-objcopy/tool-name.test.

[rupprecht]

In D102299#2753300, @jhenderson wrote:

Is it strictly ends with, or do things like file extensions, version numbers etc have an impact? See the additional test cases in https://github.com/llvm/llvm-project/blob/main/llvm/test/tools/llvm-objcopy/tool-name.test.

Strictly ends with. See https://github.com/llvm/llvm-project/blob/98575708da9544ccab8939fece9c3d638a32f09f/llvm/tools/llvm-cov/llvm-cov.cpp#L63.

I could land this as-is and copy that from llvm-objcopy so "llvm-gcov-10" would be recognized. Although I don't know how many people are relying on this -- the existence of this doesn't even seem to be in cmake configs (i.e. we don't produce *gcov symlinks like we do for llvm-strip).

llvm/test/tools/llvm-cov/tool-name.test

+## Don't make symlinks on Windows.
+# UNSUPPORTED: system-windows
+
+# RUN: rm -rf %t
+# RUN: mkdir %t
+
+## By default, assume llvm-cov.
+# RUN: ln -s llvm-cov %t/llvm-foo
+
+# RUN: llvm-cov --help 2>&1 | FileCheck --check-prefix=COV %s
+# RUN: %t/llvm-foo --help 2>&1 | FileCheck --check-prefix=COV %s
+
+# COV: Shows code coverage information.
+# COV: Subcommands:
+
+## If the filename ends in "gcov", assume gcov compatibility.
+# RUN: ln -s llvm-cov %t/llvm-gcov
+# RUN: ln -s llvm-cov %t/gcov
+
+# RUN: %t/llvm-gcov --help 2>&1 | FileCheck --check-prefix=GCOV %s
+# RUN: %t/gcov --help 2>&1 | FileCheck --check-prefix=GCOV %s
+# RUN: llvm-cov gcov --help 2>&1 | FileCheck --check-prefix=GCOV %s
+
+# GCOV: OVERVIEW: LLVM code coverage tool
+# GCOV: --gcda{{.*}}Override inferred gcda file
+# GCOV: --gcno{{.*}}Override inferred gcno file