Patchwork D11635: dirstate-v2: Replace the 32-bit `mode` field with two bits

diff --git a/rust/hg-cpython/Cargo.toml b/rust/hg-cpython/Cargo.toml
--- a/rust/hg-cpython/Cargo.toml
+++ b/rust/hg-cpython/Cargo.toml
@@ -23,7 +23,7 @@ 
 [dependencies]
 crossbeam-channel = "0.4"
 hg-core = { path = "../hg-core"}
-libc = '*'
+libc = "0.2"
 log = "0.4.8"
 env_logger = "0.7.1"
 stable_deref_trait = "1.2.0"
diff --git a/rust/hg-core/src/dirstate_tree/on_disk.rs b/rust/hg-core/src/dirstate_tree/on_disk.rs
--- a/rust/hg-core/src/dirstate_tree/on_disk.rs
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs
@@ -107,13 +107,15 @@ 
         const P2_INFO = 1 << 2;
         const HAS_MODE_AND_SIZE = 1 << 3;
         const HAS_MTIME = 1 << 4;
+        const MODE_EXEC_PERM = 1 << 5;
+        const MODE_IS_SYMLINK = 1 << 7;
     }
 }
 
 #[derive(BytesCast, Copy, Clone, Debug)]
 #[repr(C)]
 struct Entry {
-    mode: U32Be,
+    _padding: U32Be,
     size: U32Be,
     mtime: U32Be,
 }
@@ -332,13 +334,27 @@ 
         )
     }
 
+    fn synthesize_unix_mode(&self) -> u32 {
+        let file_type = if self.flags.contains(Flags::MODE_IS_SYMLINK) {
+            libc::S_IFLNK
+        } else {
+            libc::S_IFREG
+        };
+        let permisions = if self.flags.contains(Flags::MODE_EXEC_PERM) {
+            0o755
+        } else {
+            0o644
+        };
+        file_type | permisions
+    }
+
     fn assume_entry(&self) -> DirstateEntry {
         // TODO: convert through raw bits instead?
         let wdir_tracked = self.flags.contains(Flags::WDIR_TRACKED);
         let p1_tracked = self.flags.contains(Flags::P1_TRACKED);
         let p2_info = self.flags.contains(Flags::P2_INFO);
         let mode_size = if self.flags.contains(Flags::HAS_MODE_AND_SIZE) {
-            Some((self.data.mode.into(), self.data.size.into()))
+            Some((self.synthesize_unix_mode(), self.data.size.into()))
         } else {
             None
         };
@@ -400,13 +416,15 @@ 
         flags.set(Flags::WDIR_TRACKED, wdir_tracked);
         flags.set(Flags::P1_TRACKED, p1_tracked);
         flags.set(Flags::P2_INFO, p2_info);
-        let (mode, size, mtime);
+        let (size, mtime);
         if let Some((m, s)) = mode_size_opt {
-            mode = m;
+            let exec_perm = m & libc::S_IXUSR != 0;
+            let is_symlink = m & libc::S_IFMT == libc::S_IFLNK;
+            flags.set(Flags::MODE_EXEC_PERM, exec_perm);
+            flags.set(Flags::MODE_IS_SYMLINK, is_symlink);
             size = s;
             flags.insert(Flags::HAS_MODE_AND_SIZE)
         } else {
-            mode = 0;
             size = 0;
         }
         if let Some(m) = mtime_opt {
@@ -416,7 +434,7 @@ 
             mtime = 0;
         }
         let raw_entry = Entry {
-            mode: mode.into(),
+            _padding: 0.into(),
             size: size.into(),
             mtime: mtime.into(),
         };
@@ -600,7 +618,7 @@ 
                         dirstate_map::NodeData::None => (
                             Flags::empty(),
                             Entry {
-                                mode: 0.into(),
+                                _padding: 0.into(),
                                 size: 0.into(),
                                 mtime: 0.into(),
                             },
diff --git a/rust/hg-core/Cargo.toml b/rust/hg-core/Cargo.toml
--- a/rust/hg-core/Cargo.toml
+++ b/rust/hg-core/Cargo.toml
@@ -17,6 +17,7 @@ 
 im-rc = "15.0.*"
 itertools = "0.9"
 lazy_static = "1.4.0"
+libc = "0.2"
 rand = "0.7.3"
 rand_pcg = "0.2.1"
 rand_distr = "0.2.2"
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,5 +1,7 @@ 
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "adler"
 version = "0.2.3"
@@ -386,6 +388,7 @@ 
  "im-rc",
  "itertools",
  "lazy_static",
+ "libc",
  "log",
  "memmap2",
  "micro-timer",
diff --git a/mercurial/helptext/internals/dirstate-v2.txt b/mercurial/helptext/internals/dirstate-v2.txt
--- a/mercurial/helptext/internals/dirstate-v2.txt
+++ b/mercurial/helptext/internals/dirstate-v2.txt
@@ -380,6 +380,9 @@ 
     P2_INFO = 1 << 2
     HAS_MODE_AND_SIZE = 1 << 3
     HAS_MTIME = 1 << 4
+    MODE_EXEC_PERM = 1 << 5
+    MODE_IS_SYMLINK = 1 << 7
+
 
   Other bits are unset. The meaning of these bits are:
 
@@ -414,14 +417,17 @@ 
   in order to optimize `hg status`
   by enabling it to skip `readdir` in more cases.
 
-  When a node is for a file tracked anywhere,
-  the rest of the node data is three fields:
+  When a node is for a file tracked anywhere:
+  - If `HAS_MODE_AND_SIZE` is set, the file is expected
+    to be a symbolic link or a normal file based on `MODE_IS_SYMLINK`.
+  - If `HAS_MODE_AND_SIZE` is set, the file’s owner is expected
+    to have execute permission or not based on `MODE_EXEC_PERM`.
+  - If `HAS_MODE_AND_SIZE` is unset,
+    the expected type of file and permission are unknown.
+  The rest of the node data is three fields:
 
   * Offset 31:
-    If `HAS_MODE_AND_SIZE` is unset, four zero bytes.
-    Otherwise, a 32-bit integer for the Unix mode (as in `stat_result.st_mode`)
-    expected for this file to be considered clean.
-    Only the `S_IXUSR` bit (owner has execute permission) is considered.
+    4 unused bytes, set to zero
 
   * Offset 35:
     If `HAS_MODE_AND_SIZE` is unset, four zero bytes.