Add a formatter binary skeleton as P4C back end (#4710)

* init: p4 formatter

Signed-off-by: Nitish <[email protected]>

* eliminate implicit char* -> cstring conversion in `P4fmtOptions`

---------

Signed-off-by: Nitish <[email protected]>

CMakeLists.txt

@@ -40,6 +40,7 @@ OPTION (ENABLE_EBPF "Build the EBPF backend (required for the full test suite)"
 OPTION (ENABLE_UBPF "Build the uBPF backend (required for the full test suite)" ON)
 OPTION (ENABLE_DPDK "Build the DPDK backend (required for the full test suite)" ON)
 OPTION (ENABLE_P4TC "Build the P4TC backend" ON)
+OPTION (ENABLE_P4FMT "Build the P4FMT backend" ON)
 OPTION (ENABLE_P4TEST "Build the P4Test backend (required for the full test suite)" ON)
 OPTION (ENABLE_TEST_TOOLS "Build the P4Tools development platform" OFF)
 OPTION (ENABLE_P4C_GRAPHS "Build the p4c-graphs backend" ON)
@@ -479,6 +480,9 @@ endif ()
 if (ENABLE_TEST_TOOLS)
     add_subdirectory (backends/p4tools)
 endif ()
+if (ENABLE_P4FMT)
+    add_subdirectory (backends/p4fmt)
+endif ()
 if (ENABLE_UBPF)
     add_subdirectory (backends/ubpf)
 endif ()

backends/p4fmt/CMakeLists.txt

@@ -0,0 +1,14 @@
+set(FMT_SRCS
+    p4fmt.cpp
+    options.cpp
+)
+
+add_executable(p4fmt ${FMT_SRCS})
+target_link_libraries(p4fmt ${P4C_LIBRARIES} ${P4C_LIB_DEPS})
+add_dependencies(p4fmt frontend)
+
+add_custom_target(p4formatter
+        COMMAND ${CMAKE_COMMAND} -E create_symlink ${CMAKE_CURRENT_BINARY_DIR}/p4fmt ${P4C_BINARY_DIR}/p4fmt
+)
+
+add_dependencies(p4c_driver p4formatter)

backends/p4fmt/README.md

@@ -0,0 +1,27 @@
+# p4fmt (P4 Formatter)
+
+p4fmt is a WIP formatter for P4. It's in a highly experimental phase
+and, not yet stable/reliable for general use.
+Contributions and feedbacks from the community
+would be highly appreciated.
+
+## Build
+- Setup P4C correctly, from [here](https://github.com/p4lang/p4c#dependencies).
+
+- Follow the instructions here to [build](https://github.com/p4lang/p4c#installing-p4c-from-source).
+
+Later `p4fmt` executable can be found inside the `p4c/build/` dir, and can be invoked as `./build/p4fmt` from p4c's root dir.
+
+## Usage
+- Takes an output file with a `-o` flag and writes to it.
+
+    `./build/p4fmt <p4 source file> -o <output_file>`
+
+ - If an output file is not provided with `-o` flag, it just prints the output on the stdout.
+
+    `./build/p4fmt <p4 source file>`
+
+Sample Usage:
+
+    ./build/p4fmt/p4fmt sample.p4
+    ./build/p4fmt/p4fmt sample.p4 -o out.p4

backends/p4fmt/options.cpp

@@ -0,0 +1,17 @@
+#include "options.h"
+
+namespace P4Fmt {
+
+P4fmtOptions::P4fmtOptions() {
+    registerOption(
+        "-o", "outfile",
+        [this](const char *arg) {
+            outFile = cstring(arg);
+            return true;
+        },
+        "Write formatted output to outfile");
+}
+
+const cstring &P4fmtOptions::outputFile() const { return outFile; }
+
+}  // namespace P4Fmt

backends/p4fmt/options.h

@@ -0,0 +1,29 @@
+#ifndef BACKENDS_P4FMT_OPTIONS_H_
+#define BACKENDS_P4FMT_OPTIONS_H_
+
+#include "frontends/common/options.h"
+#include "frontends/common/parser_options.h"
+
+namespace P4Fmt {
+
+class P4fmtOptions : public CompilerOptions {
+ public:
+    P4fmtOptions();
+    virtual ~P4fmtOptions() = default;
+    P4fmtOptions(const P4fmtOptions &) = default;
+    P4fmtOptions(P4fmtOptions &&) = delete;
+    P4fmtOptions &operator=(const P4fmtOptions &) = default;
+    P4fmtOptions &operator=(P4fmtOptions &&) = delete;
+
+    const cstring &outputFile() const;
+
+ private:
+    /// File to output to.
+    cstring outFile = nullptr;
+};
+
+using P4FmtContext = P4CContextWithOptions<P4fmtOptions>;
+
+}  // namespace P4Fmt
+
+#endif /* BACKENDS_P4FMT_OPTIONS_H_ */

backends/p4fmt/p4fmt.cpp

@@ -0,0 +1,52 @@
+#include <cstdlib>
+
+#include "frontends/common/parseInput.h"
+#include "frontends/common/parser_options.h"
+#include "frontends/p4/toP4/toP4.h"
+#include "ir/ir.h"
+#include "lib/compile_context.h"
+#include "lib/cstring.h"
+#include "lib/error.h"
+#include "lib/nullstream.h"
+#include "options.h"
+#include "test/gtest/helpers.h"
+
+int main(int argc, char *const argv[]) {
+    AutoCompileContext autoP4FmtContext(new P4Fmt::P4FmtContext);
+    auto &options = P4Fmt::P4FmtContext::get().options();
+
+    if (options.process(argc, argv) == nullptr) {
+        return EXIT_FAILURE;
+    }
+
+    options.setInputFile();
+
+    std::ostream *out = nullptr;
+
+    // Write to stdout in absence of an output file.
+    if (options.outputFile().isNullOrEmpty()) {
+        out = &std::cout;
+    } else {
+        out = openFile(options.outputFile(), false);
+        if (!(*out)) {
+            ::error(ErrorType::ERR_NOT_FOUND, "%2%: No such file or directory.",
+                    options.outputFile());
+            options.usage();
+            return EXIT_FAILURE;
+        }
+    }
+
+    const IR::P4Program *program = P4::parseP4File(options);
+
+    if (program == nullptr && ::errorCount() != 0) {
+        return EXIT_FAILURE;
+    }
+
+    auto top4 = P4::ToP4(out, false);
+
+    *out << "\n############################## INITIAL ##############################\n";
+    // Print the program before running front end passes.
+    program->apply(top4);
+
+    return ::errorCount() > 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+}