Add infra/msvc_filter_showincludes

This is a wrapper around the cl.exe compiler for Windows MSVC toolchains.
It works around bazelbuild/bazel#19733 by filtering EngFlow execroot
directories out of MSVC's /showincludes output so Bazel does not see them.
The package documentation explains this is more detail.

For linear/PE-1127, linear/CUS-81, linear/CUS-64, linear/PE-1434

deps.bzl

@@ -3,11 +3,18 @@ deps.bzl contains macros that declare dependencies for each langauge
 that needs them.
 """
 
+load("@bazel_gazelle//:deps.bzl", "go_repository")
+
 def go_dependencies():
     """Declares Go dependencies needed by this workspace.
 
     Managed with 'bazel run //:gazelle -- update-repos -from-file=go.mod.
 
     Keep in sync with go.mod.
     """
-    pass
+    go_repository(
+        name = "com_github_google_go_cmp",
+        importpath = "github.com/google/go-cmp",
+        sum = "h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=",
+        version = "v0.6.0",
+    )

go.mod

@@ -1,3 +1,5 @@
 module github.com/EngFlow/example
 
 go 1.21.2
+
+require github.com/google/go-cmp v0.6.0

go.sum

@@ -0,0 +1,2 @@
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=

infra/msvc_filter_showincludes/BUILD

@@ -0,0 +1,26 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library", "go_test")
+
+MSVC_PATH = "C:/Program Files (x86)/Microsoft Visual Studio/2019/BuildTools/VC/Tools/MSVC/14.29.30133/bin/HostX64/x64/cl.exe"
+
+go_library(
+    name = "msvc_filter_showincludes_lib",
+    srcs = ["msvc_filter_showincludes.go"],
+    importpath = "github.com/EngFlow/example/infra/msvc_filter_showincludes",
+    visibility = ["//visibility:private"],
+    x_defs = {
+        "github.com/EngFlow/example/infra/msvc_filter_showincludes.MSVCPath": MSVC_PATH,
+    },
+)
+
+go_binary(
+    name = "msvc_filter_showincludes",
+    embed = [":msvc_filter_showincludes_lib"],
+    visibility = ["//visibility:public"],
+)
+
+go_test(
+    name = "msvc_filter_showincludes_test",
+    srcs = ["msvc_filter_showincludes_test.go"],
+    embed = [":msvc_filter_showincludes_lib"],
+    deps = ["@com_github_google_go_cmp//cmp"],
+)

infra/msvc_filter_showincludes/msvc_filter_showincludes.go

@@ -0,0 +1,222 @@
+// Command msvc_filter_showincludes relativizes output of cl.exe /showincludes.
+//
+// Work around for https://github.com/bazelbuild/bazel/issues/19733.
+//
+// Bazel's CppCompile action performs header validation as part of each compile.
+// Bazel causes the compiler to dump a complete list of headers included in each
+// compilation. Bazel post-processes this output to verify that the action
+// did not include files that weren't part of the provided inputs and
+// aren't listed in the toolchain's system include directories.
+//
+// When building with MSVC, Bazel enables the /showincludes flag, which prints
+// the list of includes on stdout or stderr (not sure which; Bazel reads both).
+// The output contains absolute paths, which is non-hermetic for remote
+// execution.
+//
+// Before performing header validation, Bazel pre-processes the output to
+// remove anything that looks like an execroot prefix. Unfortunately,
+// Bazel's idea of an execroot prefix doesn't match EngFlow's. Bazel's
+// prefix also includes a workspace name, which is not transmitted as part of
+// the remote execution protocol, so we can't work around this problem
+// on the server side.
+//
+// Instead, we can configure the C++ toolchain to invoke
+// msvc_filter_showincludes instead of cl.exe. This program wraps MSVC,
+// invoking it with a hard-coded absolute path. This program filters
+// /showincludes output, removing parts of directory paths that look like
+// EngFlow Windows execroot directories.
+//
+// For example, this line:
+//
+//	Note: including file: C:\worker\work\2\exec\cpp/hello.h
+//
+// is replaced with:
+//
+//	Note: including file: cpp/hello.h
+//
+// Bazel's validation code (HeaderDiscover.java) can still use this output.
+// This wrapper makes the action somewhat more hermetic.
+package main
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"regexp"
+	"strings"
+)
+
+// MSVCPath is the absolute path to MSVC's cl.exe. It should be set with a -X
+// linker flag. With rules_go, that can be done with an x_defs attribute.
+var MSVCPath string
+
+func main() {
+	if err := run(context.Background(), os.Args[1:]); err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func run(ctx context.Context, args []string) error {
+	cmd := exec.CommandContext(ctx, MSVCPath, args...)
+	stdoutBuf := &bytes.Buffer{}
+	stderrBuf := &bytes.Buffer{}
+	cmd.Stdout = stdoutBuf
+	cmd.Stderr = stderrBuf
+
+	if err := cmd.Run(); err != nil {
+		return err
+	}
+
+	stdoutFiltered := showIncludesRe.ReplaceAll(stdoutBuf.Bytes(), []byte(showIncludesReplacement))
+	stderrFiltered := showIncludesRe.ReplaceAll(stderrBuf.Bytes(), []byte(showIncludesReplacement))
+	if _, err := os.Stdout.Write(stdoutFiltered); err != nil {
+		return err
+	}
+	if _, err := os.Stderr.Write(stderrFiltered); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// showIncludesReplacement is the string to pass to regexp.Regexp.ReplaceAll
+// when filtering output. Substrings like $1 expand to numbered match groups.
+// This basically drops $2, the EngFlow execroot directory.
+var showIncludesReplacement = `$1$3`
+
+// showIncludesRe is the regular expression to match in the output.
+// It consists of three match groups with no text in between.
+//
+// Group 1 matches a prefix like "Note: including file:" followed by
+// whitespace. The prefix is translated into 14 languages. The bytes are
+// copied from Bazel's ShowIncludesFilter.java.
+//
+// Group 2 matches the EngFlow execroot directory prefix, ending with \.
+// It should be removed.
+//
+// Group 3 matches the include path within the execroot.
+//
+// For example, the line:
+//
+//	Note: including file: C:\worker\work\2\exec\cpp/hello.h
+//
+// is split into groups:
+//
+// 1. "Note: including file: "
+// 2. "C:\worker\work\2\exec\"
+// 3. "cpp/hello.h\n"
+var showIncludesRe = (func() *regexp.Regexp {
+	if MSVCPath == "" {
+		panic("MSVCPath was not set; expected it to be set with -X linker flag (x_defs in Bazel)")
+	}
+
+	// Flags:
+	// i: case sensitive
+	// m: ^ and $ match begin/end of line in addition to begin/end of text.
+	buf := &strings.Builder{}
+	buf.WriteString("(?im)")
+
+	// Group 1: "Note: including file:"
+	buf.WriteString("^((?:")
+	sep := ""
+	for _, prefixInt8 := range showIncludesPrefixes {
+		buf.WriteString(sep)
+		sep = "|"
+		prefixBytes := make([]byte, len(prefixInt8))
+		for i, b := range prefixInt8 {
+			prefixBytes[i] = byte(b)
+		}
+		prefixStr := regexp.QuoteMeta(string(prefixBytes))
+		buf.WriteString(prefixStr)
+	}
+	buf.WriteString(`)[ \t]*)`)
+
+	// Group 2: EngFlow execroot directory.
+	buf.WriteString(`([A-Z]:\\.*?\\exec\\)`)
+
+	// Group 3: Path within execroot.
+	buf.WriteString(`(.*\n?)`)
+	return regexp.MustCompile(buf.String())
+})()
+
+// showIncludesPrefixes is "Note: including file:" translated into 14 languages
+// and encoded in signed UTF-8. The bytes are copied from Bazel's
+// ShowIncludesFilter.java.
+var showIncludesPrefixes = [][]int8{
+	// English
+	{
+		78, 111, 116, 101, 58, 32, 105, 110, 99, 108, 117, 100, 105, 110, 103, 32, 102,
+		105, 108, 101, 58,
+	},
+	// Traditional Chinese
+	{
+		-26, -77, -88, -26, -124, -113, 58, 32, -27, -116, -123, -27, -112, -85, -26, -86,
+		-108, -26, -95, -120, 58,
+	},
+	// Czech
+	{
+		80, 111, 122, 110, -61, -95, 109, 107, 97, 58, 32, 86, -60, -115, 101, 116, 110,
+		-60, -101, 32, 115, 111, 117, 98, 111, 114, 117, 58,
+	},
+	// German
+	{
+		72, 105, 110, 119, 101, 105, 115, 58, 32, 69, 105, 110, 108, 101, 115, 101, 110,
+		32, 100, 101, 114, 32, 68, 97, 116, 101, 105, 58,
+	},
+	// French
+	{
+		82, 101, 109, 97, 114, 113, 117, 101, -62, -96, 58, 32, 105, 110, 99, 108, 117,
+		115, 105, 111, 110, 32, 100, 117, 32, 102, 105, 99, 104, 105, 101, 114, -62, -96,
+		58,
+	},
+	// Italian
+	{
+		78, 111, 116, 97, 58, 32, 102, 105, 108, 101, 32, 105, 110, 99, 108, 117, 115, 111,
+	},
+	// Japanese
+	{
+		-29, -125, -95, -29, -125, -94, 58, 32, -29, -126, -92, -29, -125, -77, -29, -126,
+		-81, -29, -125, -85, -29, -125, -68, -29, -125, -119, 32, -29, -125, -107, -29,
+		-126, -95, -29, -126, -92, -29, -125, -85, 58,
+	},
+	// Korean
+	{
+		-20, -80, -72, -22, -77, -96, 58, 32, -19, -113, -84, -19, -107, -88, 32, -19,
+		-116, -116, -20, -99, -68, 58,
+	},
+	// Polish
+	{
+		85, 119, 97, 103, 97, 58, 32, 119, 32, 116, 121, 109, 32, 112, 108, 105, 107, 117,
+		58,
+	},
+	// Portugeuse
+	{
+		79, 98, 115, 101, 114, 118, 97, -61, -89, -61, -93, 111, 58, 32, 105, 110, 99,
+		108, 117, 105, 110, 100, 111, 32, 97, 114, 113, 117, 105, 118, 111, 58,
+	},
+	// Russian
+	{
+		-48, -97, -47, -128, -48, -72, -48, -68, -48, -75, -47, -121, -48, -80, -48, -67,
+		-48, -72, -48, -75, 58, 32, -48, -78, -48, -70, -48, -69, -47, -114, -47, -121,
+		-48, -75, -48, -67, -48, -72, -48, -75, 32, -47, -124, -48, -80, -48, -71, -48,
+		-69, -48, -80, 58,
+	},
+	// Turkish
+	{
+		78, 111, 116, 58, 32, 101, 107, 108, 101, 110, 101, 110, 32, 100, 111, 115, 121,
+		97, 58,
+	},
+	// Simplified Chinese
+	{
+		-26, -77, -88, -26, -124, -113, 58, 32, -27, -116, -123, -27, -112, -85, -26,
+		-106, -121, -28, -69, -74, 58,
+	},
+	// Spanish
+	{
+		78, 111, 116, 97, 58, 32, 105, 110, 99, 108, 117, 115, 105, -61, -77, 110, 32,
+		100, 101, 108, 32, 97, 114, 99, 104, 105, 118, 111, 58,
+	},
+}