Add option and target for generating code cov info

The new `tint-generate-coverage` CMake target can be used with the clang toolchain to generate a `lcov.info` file at the root of the project, along with a `coverage.summary` human readable plain text file.

The `lcov.info` file can then be used by various tools to display code coverage information in your IDE / code editor.

Useful for ensuring decent test coverage.

Change-Id: I3d846f6da3af25d3d600d8e028f27b89e35b545f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/31121
Commit-Queue: Ben Clayton <bclayton@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

.gitignore

@@ -6,6 +6,8 @@
 .vscode
 build
 buildtools
+coverage.summary
+lcov.info
 out
 testing
 third_party/cpplint

CMakeLists.txt

@@ -39,6 +39,8 @@ option(TINT_ENABLE_MSAN "Enable memory sanitizer" OFF)
 option(TINT_ENABLE_ASAN "Enable address sanitizer" OFF)
 option(TINT_ENABLE_UBSAN "Enable undefined behaviour sanitizer" OFF)
 
+option(TINT_EMIT_COVERAGE "Emit code coverage information" OFF)
+
 option(TINT_CHECK_CHROMIUM_STYLE "Check for [chromium-style] issues during build" OFF)
 
 if(WIN32)
@@ -173,6 +175,18 @@ function(tint_default_compile_options TARGET)
     endif()
   endif()
 
+  if (${TINT_EMIT_COVERAGE})
+    if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+        target_compile_options(${TARGET} PRIVATE "--coverage")
+        target_link_options(${TARGET} PRIVATE "gcov")
+    elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+        target_compile_options(${TARGET} PRIVATE "-fprofile-instr-generate" "-fcoverage-mapping")
+        target_link_options(${TARGET} PRIVATE "-fprofile-instr-generate" "-fcoverage-mapping")
+    else()
+        message(FATAL_ERROR "Coverage generation not supported for the ${CMAKE_CXX_COMPILER_ID} toolchain")
+    endif()
+  endif()
+
   if (MSVC)
     # Specify /EHs for exception handling.
     target_compile_options(${TARGET} PRIVATE
@@ -228,3 +242,18 @@ add_custom_target(tint-format
   WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
   COMMENT "Running formatter"
   VERBATIM)
+
+
+if (${TINT_EMIT_COVERAGE} AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+  # Generates a lcov.info file at the project root.
+  # This can be used by tools such as VSCode's Coverage Gutters extension to
+  # visualize code coverage in the editor.
+  get_filename_component(CLANG_BIN_DIR ${CMAKE_C_COMPILER} DIRECTORY)
+  set(PATH_WITH_CLANG "${CLANG_BIN_DIR}:$ENV{PATH}")
+  add_custom_target(tint-generate-coverage
+    COMMAND ${CMAKE_COMMAND} -E env PATH=${PATH_WITH_CLANG} ./tools/tint-generate-coverage $<TARGET_FILE:tint_unittests>
+    DEPENDS tint_unittests
+    WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+    COMMENT "Generating tint coverage data"
+    VERBATIM)
+endif()

tools/tint-generate-coverage

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# Copyright 2020 The Tint Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# See https://clang.llvm.org/docs/SourceBasedCodeCoverage.html
+
+set -e # Fail on any error.
+
+if [ ! -x "$(which llvm-profdata)" ] ; then
+    echo "error: llvm-profdata needs to be on \$PATH to use $0"
+    exit 1
+fi
+
+if [ ! -x "$(which llvm-cov)" ] ; then
+    echo "error: llvm-cov needs to be on \$PATH to use $0"
+    exit 1
+fi
+
+TARGET_EXE=$1
+
+if [ ! -x "$TARGET_EXE" ] ; then
+    echo "Usage: $0 <executable-path> [optional-args]"
+    echo ""
+    echo "Generates a lcov.info file at the project root, which can be used by"
+    echo "tools such as VSCode's Coverage Gutters extension to visualize code"
+    echo "coverage in the editor".
+    exit 1
+fi
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd )"
+ROOT_DIR="$( cd "${SCRIPT_DIR}/.." >/dev/null 2>&1 && pwd )"
+
+PROFRAW_FILE="${ROOT_DIR}/tint.profraw"
+PROFDATA_FILE="${ROOT_DIR}/tint.profdata"
+LCOV_FILE="${ROOT_DIR}/lcov.info"
+SUMMARY_FILE="${ROOT_DIR}/coverage.summary"
+
+# Run the executable to generate the raw coverage data
+# https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#running-the-instrumented-program
+LLVM_PROFILE_FILE="${PROFRAW_FILE}" $@
+
+# Index the coverage data
+# https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#creating-coverage-reports
+llvm-profdata merge -sparse "${PROFRAW_FILE}" -o "${PROFDATA_FILE}"
+
+# Export as lcov
+# https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#exporting-coverage-data
+llvm-cov export --instr-profile="${PROFDATA_FILE}" --format=lcov --object=${TARGET_EXE} > "${LCOV_FILE}"
+
+# Generate summary report
+llvm-cov report --ignore-filename-regex="(.*_test\.cc|third_party/.*)" --instr-profile="${PROFDATA_FILE}" --object=${TARGET_EXE} > "${SUMMARY_FILE}"
+
+# Clean up
+rm ${PROFRAW_FILE} ${PROFDATA_FILE}