[Support] Add a new path style for Windows with forward slashes

This behaves just like the regular Windows style, with both separator
forms accepted, but with get_separator() returning forward slashes.

Add a more descriptive name for the existing style, keeping the old
name around as an alias initially.

Add a new function `make_preferred()` (like the C++17
`std::filesystem::path` function with the same name), which converts
windows paths to the preferred separator form (while this one works on
any platform and takes a `path::Style` argument).

Contrary to `native()` (just like `make_preferred()` in `std::filesystem`),
this doesn't do anything at all on Posix, it doesn't try to reinterpret
backslashes into forward slashes there.

Differential Revision: https://reviews.llvm.org/D111879

llvm/include/llvm/Support/Path.h

@@ -25,7 +25,13 @@ namespace llvm {
 namespace sys {
 namespace path {
 
-enum class Style { windows, posix, native };
+enum class Style {
+  native,
+  posix,
+  windows_slash,
+  windows_backslash,
+  windows = windows_backslash, // deprecated
+};
 
 /// Check if \p S uses POSIX path rules.
 constexpr bool is_style_posix(Style S) {
@@ -257,6 +263,17 @@ void native(const Twine &path, SmallVectorImpl<char> &result,
 /// @param path A path that is transformed to native format.
 void native(SmallVectorImpl<char> &path, Style style = Style::native);
 
+/// For Windows path styles, convert path to use the preferred path separators.
+/// For other styles, do nothing.
+///
+/// @param path A path that is transformed to preferred format.
+inline void make_preferred(SmallVectorImpl<char> &path,
+                           Style style = Style::native) {
+  if (!is_style_windows(style))
+    return;
+  native(path, style);
+}
+
 /// Replaces backslashes with slashes if Windows.
 ///
 /// @param path processed path

llvm/lib/Support/Path.cpp

@@ -37,13 +37,15 @@ namespace {
   using llvm::sys::path::Style;
 
   inline Style real_style(Style style) {
+    if (style != Style::native)
+      return style;
     if (is_style_posix(style))
       return Style::posix;
     return Style::windows;
   }
 
   inline const char *separators(Style style) {
-    if (real_style(style) == Style::windows)
+    if (is_style_windows(style))
       return "\\/";
     return "/";
   }
@@ -547,7 +549,9 @@ void native(SmallVectorImpl<char> &Path, Style style) {
   if (Path.empty())
     return;
   if (is_style_windows(style)) {
-    std::replace(Path.begin(), Path.end(), '/', '\\');
+    for (char &Ch : Path)
+      if (is_separator(Ch, style))
+        Ch = preferred_separator(style);
     if (Path[0] == '~' && (Path.size() == 1 || is_separator(Path[1], style))) {
       SmallString<128> PathHome;
       home_directory(PathHome);
@@ -601,7 +605,7 @@ bool is_separator(char value, Style style) {
 }
 
 StringRef get_separator(Style style) {
-  if (is_style_windows(style))
+  if (real_style(style) == Style::windows)
     return "\\";
   return "/";
 }

llvm/unittests/Support/Path.cpp

@@ -75,7 +75,9 @@ TEST(is_style_Style, Works) {
   // Check platform-independent results.
   EXPECT_TRUE(is_style_posix(Style::posix));
   EXPECT_TRUE(is_style_windows(Style::windows));
+  EXPECT_TRUE(is_style_windows(Style::windows_slash));
   EXPECT_FALSE(is_style_posix(Style::windows));
+  EXPECT_FALSE(is_style_posix(Style::windows_slash));
   EXPECT_FALSE(is_style_windows(Style::posix));
 
   // Check platform-dependent results.
@@ -95,12 +97,19 @@ TEST(is_separator, Works) {
   EXPECT_FALSE(path::is_separator(' '));
 
   EXPECT_TRUE(path::is_separator('\\', path::Style::windows));
+  EXPECT_TRUE(path::is_separator('\\', path::Style::windows_slash));
   EXPECT_FALSE(path::is_separator('\\', path::Style::posix));
 
   EXPECT_EQ(path::is_style_windows(path::Style::native),
             path::is_separator('\\'));
 }
 
+TEST(get_separator, Works) {
+  EXPECT_EQ(path::get_separator(path::Style::posix), "/");
+  EXPECT_EQ(path::get_separator(path::Style::windows_backslash), "\\");
+  EXPECT_EQ(path::get_separator(path::Style::windows_slash), "/");
+}
+
 TEST(is_absolute_gnu, Works) {
   // Test tuple <Path, ExpectedPosixValue, ExpectedWindowsValue>.
   const std::tuple<StringRef, bool, bool> Paths[] = {
@@ -383,6 +392,8 @@ TEST(Support, PathIterator) {
               testing::ElementsAre("/", ".c", ".d", "..", "."));
   EXPECT_THAT(GetComponents("c:\\c\\e\\foo.txt", path::Style::windows),
               testing::ElementsAre("c:", "\\", "c", "e", "foo.txt"));
+  EXPECT_THAT(GetComponents("c:\\c\\e\\foo.txt", path::Style::windows_slash),
+              testing::ElementsAre("c:", "\\", "c", "e", "foo.txt"));
   EXPECT_THAT(GetComponents("//net/"), testing::ElementsAre("//net", "/"));
   EXPECT_THAT(GetComponents("//net/c/foo.txt"),
               testing::ElementsAre("//net", "/", "c", "foo.txt"));
@@ -1425,10 +1436,25 @@ TEST(Support, NormalizePath) {
   for (auto &T : Tests) {
     SmallString<64> Win(std::get<0>(T));
     SmallString<64> Posix(Win);
+    SmallString<64> WinSlash(Win);
     path::native(Win, path::Style::windows);
     path::native(Posix, path::Style::posix);
+    path::native(WinSlash, path::Style::windows_slash);
     EXPECT_EQ(std::get<1>(T), Win);
     EXPECT_EQ(std::get<2>(T), Posix);
+    EXPECT_EQ(std::get<2>(T), WinSlash);
+  }
+
+  for (auto &T : Tests) {
+    SmallString<64> WinBackslash(std::get<0>(T));
+    SmallString<64> Posix(WinBackslash);
+    SmallString<64> WinSlash(WinBackslash);
+    path::make_preferred(WinBackslash, path::Style::windows_backslash);
+    path::make_preferred(Posix, path::Style::posix);
+    path::make_preferred(WinSlash, path::Style::windows_slash);
+    EXPECT_EQ(std::get<1>(T), WinBackslash);
+    EXPECT_EQ(std::get<0>(T), Posix); // Posix remains unchanged here
+    EXPECT_EQ(std::get<2>(T), WinSlash);
   }
 
 #if defined(_WIN32)
@@ -1437,10 +1463,15 @@ TEST(Support, NormalizePath) {
 
   const char *Path7a = "~/aaa";
   SmallString<64> Path7(Path7a);
-  path::native(Path7);
+  path::native(Path7, path::Style::windows_backslash);
   EXPECT_TRUE(Path7.endswith("\\aaa"));
   EXPECT_TRUE(Path7.startswith(PathHome));
   EXPECT_EQ(Path7.size(), PathHome.size() + strlen(Path7a + 1));
+  Path7 = Path7a;
+  path::native(Path7, path::Style::windows_slash);
+  EXPECT_TRUE(Path7.endswith("/aaa"));
+  EXPECT_TRUE(Path7.startswith(PathHome));
+  EXPECT_EQ(Path7.size(), PathHome.size() + strlen(Path7a + 1));
 
   const char *Path8a = "~";
   SmallString<64> Path8(Path8a);
@@ -1454,7 +1485,7 @@ TEST(Support, NormalizePath) {
 
   const char *Path10a = "aaa/~/b";
   SmallString<64> Path10(Path10a);
-  path::native(Path10);
+  path::native(Path10, path::Style::windows_backslash);
   EXPECT_EQ(Path10, "aaa\\~\\b");
 #endif
 }