build: support compiling for non-Unix targets such as wasm

The platform-specific code was split into cfg(unix)/cfg(windows) arms, so
wasm32 targets (which are neither) failed to compile. Widen the generic
Windows stubs to cfg(not(unix)) and make the -ls printer and xargs size
limiters fall back to portable APIs when no platform-specific one exists.

src/find/matchers/group.rs

@@ -11,6 +11,8 @@ use nix::unistd::Group;
 use std::os::unix::fs::MetadataExt;
 
 pub struct GroupMatcher {
+    // Only read on Unix; the non-Unix `matches` implementation is a stub.
+    #[cfg_attr(not(unix), allow(dead_code))]
     gid: ComparableValue,
 }
 
@@ -31,7 +33,7 @@ impl GroupMatcher {
         Self { gid }
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     pub fn from_group_name(_group: &str) -> Option<Self> {
         None
     }
@@ -46,10 +48,10 @@ impl Matcher for GroupMatcher {
         }
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     fn matches(&self, _file_info: &WalkEntry, _: &mut MatcherIO) -> bool {
-        // The user group acquisition function for Windows systems is not implemented in MetadataExt,
-        // so it is somewhat difficult to implement it. :(
+        // The user group acquisition function for non-Unix systems is not implemented in
+        // MetadataExt, so it is somewhat difficult to implement it. :(
         false
     }
 }
@@ -80,7 +82,7 @@ impl Matcher for NoGroupMatcher {
         false
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     fn matches(&self, _file_info: &WalkEntry, _: &mut MatcherIO) -> bool {
         false
     }

src/find/matchers/ls.rs

@@ -195,7 +195,7 @@ impl Ls {
         }
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     fn print(
         &self,
         file_info: &WalkEntry,
@@ -203,16 +203,15 @@ impl Ls {
         mut out: impl Write,
         print_error_message: bool,
     ) {
-        use std::os::windows::fs::MetadataExt;
-
+        // Non-Unix targets (Windows, wasm, ...) don't expose inode, owner,
+        // group or Unix permission bits, so those columns are left blank.
         let metadata = file_info.metadata().unwrap();
 
         let inode_number = 0;
+        let size = metadata.len();
         let number_of_blocks = {
-            let size = metadata.file_size();
             let number_of_blocks = size / 1024;
             let remainder = number_of_blocks % 4;
-
             if remainder == 0 {
                 if number_of_blocks == 0 {
                     4
@@ -220,14 +219,19 @@ impl Ls {
                     number_of_blocks
                 }
             } else {
-                number_of_blocks + (4 - (remainder))
+                number_of_blocks + (4 - remainder)
             }
         };
-        let permission = { format_permissions(metadata.file_attributes()) };
+        #[cfg(windows)]
+        let permission = {
+            use std::os::windows::fs::MetadataExt;
+            format_permissions(metadata.file_attributes())
+        };
+        #[cfg(not(windows))]
+        let permission = "?---------";
         let hard_links = 0;
         let user = 0;
         let group = 0;
-        let size = metadata.file_size();
         let last_modified = {
             let system_time = metadata.modified().unwrap();
             let now_utc: DateTime<chrono::Utc> = system_time.into();
@@ -235,9 +239,9 @@ impl Ls {
         };
         let path = file_info.path().to_string_lossy();
 
-        match write!(
+        match writeln!(
             out,
-            " {:<4} {:>6} {:<10} {:>3} {:<8} {:<8} {:>8} {} {}\n",
+            " {:<4} {:>6} {:<10} {:>3} {:<8} {:<8} {:>8} {} {}",
             inode_number,
             number_of_blocks,
             permission,

src/find/matchers/name.rs

@@ -31,7 +31,7 @@ impl Matcher for NameMatcher {
             self.pattern.matches(&name)
         }
 
-        #[cfg(windows)]
+        #[cfg(not(unix))]
         self.pattern.matches(&name)
     }
 }

src/find/matchers/perm.rs

@@ -91,7 +91,7 @@ impl PermMatcher {
     }
 
     #[cfg(not(unix))]
-    pub fn new(_dummy_pattern: &str) -> Result<PermMatcher, Box<dyn Error>> {
+    pub fn new(_dummy_pattern: &str) -> Result<Self, Box<dyn Error>> {
         Err(From::from(
             "Permission matching is not available on this platform",
         ))
@@ -132,7 +132,7 @@ impl Matcher for PermMatcher {
             "Permission matching not available on this platform!"
         )
         .unwrap();
-        return false;
+        false
     }
 }
 

src/find/matchers/printf.rs

@@ -17,6 +17,7 @@ use super::{FileType, Matcher, MatcherIO, WalkEntry, WalkError};
 #[cfg(unix)]
 use std::os::unix::prelude::MetadataExt;
 
+#[cfg(unix)]
 const STANDARD_BLOCK_SIZE: u64 = 512;
 
 #[derive(Debug, PartialEq, Eq)]

src/find/matchers/user.rs

@@ -11,6 +11,8 @@ use nix::unistd::User;
 use std::os::unix::fs::MetadataExt;
 
 pub struct UserMatcher {
+    // Only read on Unix; the non-Unix `matches` implementation is a stub.
+    #[cfg_attr(not(unix), allow(dead_code))]
     uid: ComparableValue,
 }
 
@@ -31,7 +33,7 @@ impl UserMatcher {
         Self { uid }
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     pub fn from_user_name(_user: &str) -> Option<Self> {
         None
     }
@@ -46,7 +48,7 @@ impl Matcher for UserMatcher {
         }
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     fn matches(&self, _file_info: &WalkEntry, _: &mut MatcherIO) -> bool {
         false
     }
@@ -78,7 +80,7 @@ impl Matcher for NoUserMatcher {
         false
     }
 
-    #[cfg(windows)]
+    #[cfg(not(unix))]
     fn matches(&self, _file_info: &WalkEntry, _: &mut MatcherIO) -> bool {
         false
     }

src/find/mod.rs

@@ -9,7 +9,9 @@ pub mod matchers;
 use matchers::{Follow, WalkEntry};
 use std::cell::RefCell;
 use std::error::Error;
-use std::io::{self, stderr, stdout, BufRead, BufReader, IsTerminal, Write};
+#[cfg(unix)]
+use std::io::IsTerminal;
+use std::io::{self, stderr, stdout, BufRead, BufReader, Write};
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::time::SystemTime;

src/xargs/mod.rs

@@ -152,6 +152,12 @@ fn count_osstr_chars_for_exec(s: &OsStr) -> usize {
     s.as_bytes().len() + 1
 }
 
+#[cfg(not(any(unix, windows)))]
+fn count_osstr_chars_for_exec(s: &OsStr) -> usize {
+    // Include +1 for the null terminator.
+    s.as_encoded_bytes().len() + 1
+}
+
 #[derive(Clone)]
 struct MaxCharsCommandSizeLimiter {
     current_size: usize,
@@ -187,6 +193,14 @@ impl MaxCharsCommandSizeLimiter {
 
         Self::new(arg_max - ARG_HEADROOM - env_size)
     }
+
+    #[cfg(not(any(unix, windows)))]
+    fn new_system(_env: &HashMap<OsString, OsString>) -> Self {
+        // No portable way to query the system limit; fall back to the POSIX
+        // minimum guaranteed value for _POSIX_ARG_MAX.
+        const POSIX_ARG_MAX: usize = 4096;
+        Self::new(POSIX_ARG_MAX)
+    }
 }
 
 impl CommandSizeLimiter for MaxCharsCommandSizeLimiter {