Revert "Merge pull request #21540 from BratishkaErik/search-env-in-path"

It caused an assertion failure when building Zig from source.

This reverts commit 0595feb34128db22fbebea843af929de3ede8190, reversing
changes made to 744771d3303e122474a72c8a94b14fe1e9fb480c.

closes #22566
closes #22568

2 files changed, 114 insertions, 141 deletions

diff --git a/lib/std/fs/path.zig b/lib/std/fs/path.zig
index f0f60a2ff1..3376771313 100644
--- a/lib/std/fs/path.zig
+++ b/lib/std/fs/path.zig
@@ -90,7 +90,9 @@ fn joinSepMaybeZ(allocator: Allocator, separator: u8, comptime sepPredicate: fn
         var sum: usize = paths[first_path_index].len;
         var prev_path = paths[first_path_index];
         assert(prev_path.len > 0);
-        for (paths[first_path_index + 1 ..]) |this_path| {
+        var i: usize = first_path_index + 1;
+        while (i < paths.len) : (i += 1) {
+            const this_path = paths[i];
             if (this_path.len == 0) continue;
             const prev_sep = sepPredicate(prev_path[prev_path.len - 1]);
             const this_sep = sepPredicate(this_path[0]);
@@ -110,7 +112,9 @@ fn joinSepMaybeZ(allocator: Allocator, separator: u8, comptime sepPredicate: fn
     var buf_index: usize = paths[first_path_index].len;
     var prev_path = paths[first_path_index];
     assert(prev_path.len > 0);
-    for (paths[first_path_index + 1 ..]) |this_path| {
+    var i: usize = first_path_index + 1;
+    while (i < paths.len) : (i += 1) {
+        const this_path = paths[i];
         if (this_path.len == 0) continue;
         const prev_sep = sepPredicate(prev_path[prev_path.len - 1]);
         const this_sep = sepPredicate(this_path[0]);
diff --git a/lib/std/zig/system.zig b/lib/std/zig/system.zig
index 2376334c5c..68182366e8 100644
--- a/lib/std/zig/system.zig
+++ b/lib/std/zig/system.zig
@@ -995,106 +995,6 @@ fn glibcVerFromSoFile(file: fs.File) !std.SemanticVersion {
     return max_ver;
 }
 
-/// This functions tries to open file located at `start_path`, and then guesses
-/// whether it is a script or an ELF file.
-///
-/// If it finds "shebang line", file is considered a script, and logic is re-run
-/// using interpreter referenced after "#!" symbols. If interpreter is itself also a script,
-/// logic becomes recursive until non-script file is found.
-///
-/// If it finds ELF magic sequence, file is considered an ELF file and function returns.
-fn resolveElfFileRecursively(cwd: fs.Dir, start_path: []const u8) error{UnableToFindElfFile}!fs.File {
-    var current_path = start_path;
-
-    // According to `man 2 execve`:
-    //
-    // The kernel imposes a maximum length on the text
-    // that follows the "#!" characters at the start of a script;
-    // characters beyond the limit are ignored.
-    // Before Linux 5.1, the limit is 127 characters.
-    // Since Linux 5.1, the limit is 255 characters.
-    //
-    // Tests show that bash and zsh consider 255 as total limit,
-    // *including* "#!" characters and ignoring newline.
-    // For safety, we set max length as 255 + \n (1).
-    var buffer: [255 + 1]u8 = undefined;
-    while (true) {
-        // Interpreter path can be relative on Linux, but
-        // for simplicity we are asserting it is an absolute path.
-        assert(std.fs.path.isAbsolute(current_path));
-        const file = cwd.openFile(current_path, .{}) catch |err| switch (err) {
-            error.NoSpaceLeft => unreachable,
-            error.NameTooLong => unreachable,
-            error.PathAlreadyExists => unreachable,
-            error.SharingViolation => unreachable,
-            error.InvalidUtf8 => unreachable, // WASI only
-            error.InvalidWtf8 => unreachable, // Windows only
-            error.BadPathName => unreachable,
-            error.PipeBusy => unreachable,
-            error.FileLocksNotSupported => unreachable,
-            error.WouldBlock => unreachable,
-            error.FileBusy => unreachable, // opened without write permissions
-            error.AntivirusInterference => unreachable, // Windows-only error
-
-            error.IsDir,
-            error.NotDir,
-
-            error.AccessDenied,
-            error.DeviceBusy,
-            error.FileTooBig,
-            error.SymLinkLoop,
-            error.ProcessFdQuotaExceeded,
-            error.SystemFdQuotaExceeded,
-            error.SystemResources,
-
-            error.FileNotFound,
-            error.NetworkNotFound,
-            error.NoDevice,
-            error.Unexpected,
-            => return error.UnableToFindElfFile,
-        };
-        var is_elf_file = false;
-        defer if (is_elf_file == false) file.close();
-
-        // Shortest working interpreter path is "#!/i" (4)
-        // (interpreter is "/i", assuming all paths are absolute, like in above comment).
-        // ELF magic number length is also 4.
-        //
-        // If file is shorter than that, it is definitely not ELF file
-        // nor file with "shebang" line.
-        const min_len = 4;
-
-        const len = preadAtLeast(file, &buffer, 0, min_len) catch return error.UnableToFindElfFile;
-        const content = buffer[0..len];
-
-        if (mem.eql(u8, content[0..4], std.elf.MAGIC)) {
-            // It is very likely ELF file!
-            is_elf_file = true;
-            return file;
-        } else if (mem.eql(u8, content[0..2], "#!")) {
-            // We detected shebang, now parse entire line.
-
-            // Trim leading "#!", spaces and tabs.
-            const trimmed_line = mem.trimLeft(u8, content[2..], &.{ ' ', '\t' });
-
-            // This line can have:
-            // * Interpreter path only,
-            // * Interpreter path and arguments, all separated by space, tab or NUL character.
-            // And optionally newline at the end.
-            const path_maybe_args = mem.trimRight(u8, trimmed_line, "\n");
-
-            // Separate path and args.
-            const path_end = mem.indexOfAny(u8, path_maybe_args, &.{ ' ', '\t', 0 }) orelse path_maybe_args.len;
-
-            current_path = path_maybe_args[0..path_end];
-            continue;
-        } else {
-            // Not a ELF file, not a shell script with "shebang line", invalid duck.
-            return error.UnableToFindElfFile;
-        }
-    }
-}
-
 /// In the past, this function attempted to use the executable's own binary if it was dynamically
 /// linked to answer both the C ABI question and the dynamic linker question. However, this
 /// could be problematic on a system that uses a RUNPATH for the compiler binary, locking
@@ -1103,14 +1003,11 @@ fn resolveElfFileRecursively(cwd: fs.Dir, start_path: []const u8) error{UnableTo
 /// the dynamic linker will match that of the compiler binary. Executables with these versions
 /// mismatching will fail to run.
 ///
-/// Therefore, this function now does not inspect the executable's own binary.
-/// Instead, it tries to find `env` program in PATH or in hardcoded location, and uses it
-/// to find suitable ELF file. If `env` program is an executable, work is done and function starts to
-/// inspect inner structure of a file. But if `env` is a script or other non-ELF file, it uses
-/// interpreter path instead and tries to search ELF file again, going recursively in case interpreter
-/// is also a script/non-ELF file.
-///
-/// If nothing was found, then the function falls back to defaults.
+/// Therefore, this function works the same regardless of whether the compiler binary is
+/// dynamically or statically linked. It inspects `/usr/bin/env` as an ELF file to find the
+/// answer to these questions, or if there is a shebang line, then it chases the referenced
+/// file recursively. If that does not provide the answer, then the function falls back to
+/// defaults.
 fn detectAbiAndDynamicLinker(
     cpu: Target.Cpu,
     os: Target.Os,
@@ -1178,33 +1075,14 @@ fn detectAbiAndDynamicLinker(
 
     const ld_info_list = ld_info_list_buffer[0..ld_info_list_len];
 
-    const cwd = std.fs.cwd();
-
-    // Algorithm is:
-    // 1a) try_path: If PATH is non-empty and `env` file was found in one of the directories, use that.
-    // 1b) try_path: If `env` was not found or PATH is empty, try hardcoded path below.
-    // 2a) try_hardcoded: If `env` was found in hardcoded location, use that.
-    // 2b) try_hardcoded: If `env` was not found, fall back to default ABI and dynamic linker.
-    // Source: https://github.com/ziglang/zig/issues/14146#issuecomment-2308984936
-    const elf_file = (try_path: {
-        const PATH = std.posix.getenv("PATH") orelse break :try_path null;
-        var it = mem.tokenizeScalar(u8, PATH, fs.path.delimiter);
-
-        var buf: [std.fs.max_path_bytes + 1]u8 = undefined;
-        var fbs: std.heap.FixedBufferAllocator = .init(&buf);
-        const allocator = fbs.allocator();
-
-        while (it.next()) |path| : (fbs.reset()) {
-            const start_path = std.fs.path.joinZ(allocator, &.{ path, "env" }) catch |err| switch (err) {
-                error.OutOfMemory => continue,
-            };
+    // Best case scenario: the executable is dynamically linked, and we can iterate
+    // over our own shared objects and find a dynamic linker.
+    const elf_file = elf_file: {
+        // This block looks for a shebang line in /usr/bin/env,
+        // if it finds one, then instead of using /usr/bin/env as the ELF file to examine, it uses the file it references instead,
+        // doing the same logic recursively in case it finds another shebang line.
 
-            break :try_path resolveElfFileRecursively(cwd, start_path) catch |err| switch (err) {
-                error.UnableToFindElfFile => continue,
-            };
-        } else break :try_path null;
-    } orelse try_hardcoded: {
-        const hardcoded_file_name = switch (os.tag) {
+        var file_name: []const u8 = switch (os.tag) {
             // Since /usr/bin/env is hard-coded into the shebang line of many portable scripts, it's a
             // reasonably reliable path to start with.
             else => "/usr/bin/env",
@@ -1212,10 +1090,98 @@ fn detectAbiAndDynamicLinker(
             .haiku => "/bin/env",
         };
 
-        break :try_hardcoded resolveElfFileRecursively(cwd, hardcoded_file_name) catch |err| switch (err) {
-            error.UnableToFindElfFile => null,
-        };
-    }) orelse return defaultAbiAndDynamicLinker(cpu, os, query);
+        // According to `man 2 execve`:
+        //
+        // The kernel imposes a maximum length on the text
+        // that follows the "#!" characters at the start of a script;
+        // characters beyond the limit are ignored.
+        // Before Linux 5.1, the limit is 127 characters.
+        // Since Linux 5.1, the limit is 255 characters.
+        //
+        // Tests show that bash and zsh consider 255 as total limit,
+        // *including* "#!" characters and ignoring newline.
+        // For safety, we set max length as 255 + \n (1).
+        var buffer: [255 + 1]u8 = undefined;
+        while (true) {
+            // Interpreter path can be relative on Linux, but
+            // for simplicity we are asserting it is an absolute path.
+            const file = fs.openFileAbsolute(file_name, .{}) catch |err| switch (err) {
+                error.NoSpaceLeft => unreachable,
+                error.NameTooLong => unreachable,
+                error.PathAlreadyExists => unreachable,
+                error.SharingViolation => unreachable,
+                error.InvalidUtf8 => unreachable, // WASI only
+                error.InvalidWtf8 => unreachable, // Windows only
+                error.BadPathName => unreachable,
+                error.PipeBusy => unreachable,
+                error.FileLocksNotSupported => unreachable,
+                error.WouldBlock => unreachable,
+                error.FileBusy => unreachable, // opened without write permissions
+                error.AntivirusInterference => unreachable, // Windows-only error
+
+                error.IsDir,
+                error.NotDir,
+                error.AccessDenied,
+                error.NoDevice,
+                error.FileNotFound,
+                error.NetworkNotFound,
+                error.FileTooBig,
+                error.Unexpected,
+                => |e| {
+                    std.log.warn("Encountered error: {s}, falling back to default ABI and dynamic linker.", .{@errorName(e)});
+                    return defaultAbiAndDynamicLinker(cpu, os, query);
+                },
+
+                else => |e| return e,
+            };
+            var is_elf_file = false;
+            defer if (is_elf_file == false) file.close();
+
+            // Shortest working interpreter path is "#!/i" (4)
+            // (interpreter is "/i", assuming all paths are absolute, like in above comment).
+            // ELF magic number length is also 4.
+            //
+            // If file is shorter than that, it is definitely not ELF file
+            // nor file with "shebang" line.
+            const min_len: usize = 4;
+
+            const len = preadAtLeast(file, &buffer, 0, min_len) catch |err| switch (err) {
+                error.UnexpectedEndOfFile,
+                error.UnableToReadElfFile,
+                error.ProcessNotFound,
+                => return defaultAbiAndDynamicLinker(cpu, os, query),
+
+                else => |e| return e,
+            };
+            const content = buffer[0..len];
+
+            if (mem.eql(u8, content[0..4], std.elf.MAGIC)) {
+                // It is very likely ELF file!
+                is_elf_file = true;
+                break :elf_file file;
+            } else if (mem.eql(u8, content[0..2], "#!")) {
+                // We detected shebang, now parse entire line.
+
+                // Trim leading "#!", spaces and tabs.
+                const trimmed_line = mem.trimLeft(u8, content[2..], &.{ ' ', '\t' });
+
+                // This line can have:
+                // * Interpreter path only,
+                // * Interpreter path and arguments, all separated by space, tab or NUL character.
+                // And optionally newline at the end.
+                const path_maybe_args = mem.trimRight(u8, trimmed_line, "\n");
+
+                // Separate path and args.
+                const path_end = mem.indexOfAny(u8, path_maybe_args, &.{ ' ', '\t', 0 }) orelse path_maybe_args.len;
+
+                file_name = path_maybe_args[0..path_end];
+                continue;
+            } else {
+                // Not a ELF file, not a shell script with "shebang line", invalid duck.
+                return defaultAbiAndDynamicLinker(cpu, os, query);
+            }
+        }
+    };
     defer elf_file.close();
 
     // TODO: inline this function and combine the buffer we already read above to find
@@ -1239,7 +1205,10 @@ fn detectAbiAndDynamicLinker(
         error.UnexpectedEndOfFile,
         error.NameTooLong,
         // Finally, we fall back on the standard path.
-        => defaultAbiAndDynamicLinker(cpu, os, query),
+        => |e| {
+            std.log.warn("Encountered error: {s}, falling back to default ABI and dynamic linker.", .{@errorName(e)});
+            return defaultAbiAndDynamicLinker(cpu, os, query);
+        },
     };
 }