enforce import/embed case sensitivity

lib/std/Build/Cache/Path.zig

@@ -86,6 +86,16 @@ pub fn makeOpenPath(p: Path, sub_path: []const u8, opts: fs.Dir.OpenOptions) !fs
     return p.root_dir.handle.makeOpenPath(joined_path, opts);
 }
 
+pub fn realpath(p: Path, sub_path: []const u8, out_buffer: []u8) std.fs.Dir.RealPathError![]u8 {
+    var buf: [fs.max_path_bytes]u8 = undefined;
+    const joined_path = if (p.sub_path.len == 0) sub_path else p: {
+        break :p std.fmt.bufPrint(&buf, "{s}" ++ fs.path.sep_str ++ "{s}", .{
+            p.sub_path, sub_path,
+        }) catch return error.NameTooLong;
+    };
+    return p.root_dir.handle.realpath(joined_path, out_buffer);
+}
+
 pub fn statFile(p: Path, sub_path: []const u8) !fs.Dir.Stat {
     var buf: [fs.max_path_bytes]u8 = undefined;
     const joined_path = if (p.sub_path.len == 0) sub_path else p: {

lib/std/fs/path.zig

@@ -1412,8 +1412,8 @@ pub fn ComponentIterator(comptime path_type: PathType, comptime T: type) type {
 
         /// After `init`, `next` will return the first component after the root
         /// (there is no need to call `first` after `init`).
-        /// To iterate backwards (from the end of the path to the beginning), call `last`
-        /// after `init` and then iterate via `previous` calls.
+        /// To iterate backwards (from the end of the path to the beginning), call either `last`
+        /// or `moveToEnd` after `init` and then iterate via `previous` calls.
         /// For Windows paths, `error.BadPathName` is returned if the `path` has an explicit
         /// namespace prefix (`\\.\`, `\\?\`, or `\??\`) or if it is a UNC path with more
         /// than two path separators at the beginning.
@@ -1518,6 +1518,12 @@ pub fn ComponentIterator(comptime path_type: PathType, comptime T: type) type {
             };
         }
 
+        /// Moves to the end of the path. Used to iterate backwards.
+        pub fn moveToEnd(self: *Self) void {
+            self.start_index = self.path.len;
+            self.end_index = self.path.len;
+        }
+
         /// Returns the last component (from the end of the path).
         /// For example, if the path is `/a/b/c` then this will return the `c` component.
         /// After calling `last`, `next` will always return `null`, and `previous` will return
@@ -1983,3 +1989,97 @@ pub const fmtAsUtf8Lossy = std.unicode.fmtUtf8;
 /// a lossy conversion if the path contains any unpaired surrogates.
 /// Unpaired surrogates are replaced by the replacement character (U+FFFD).
 pub const fmtWtf16LeAsUtf8Lossy = std.unicode.fmtUtf16Le;
+
+test "filesystem case sensitivity" {
+    // disabled on wasi because realpath is not implemented
+    if (builtin.os.tag == .wasi) return;
+
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+
+    const fs_case_sensitive = try testIsFilesystemCaseSensitive(tmp.dir);
+    switch (builtin.os.tag) {
+        .windows, .macos => try std.testing.expectEqual(false, fs_case_sensitive),
+        else => {},
+    }
+
+    {
+        {
+            const f = try tmp.dir.createFile("foo.zig", .{});
+            f.close();
+        }
+        try std.testing.expect(try realpathMatches(tmp.dir, "foo.zig"));
+        if (fs_case_sensitive) {
+            try std.testing.expectError(error.FileNotFound, realpathMatches(tmp.dir, "Foo.zig"));
+        } else {
+            try std.testing.expect(!try realpathMatches(tmp.dir, "Foo.zig"));
+        }
+    }
+
+    try tmp.dir.makeDir("subdir");
+    {
+        {
+            const f = try tmp.dir.createFile("subdir/bar.zig", .{});
+            f.close();
+        }
+        try std.testing.expect(try realpathMatches(tmp.dir, "subdir/bar.zig"));
+        inline for (&.{
+            "Subdir/bar.zig",
+            "subdir/Bar.zig",
+        }) |sub_path| {
+            if (fs_case_sensitive) {
+                try std.testing.expectError(error.FileNotFound, realpathMatches(tmp.dir, sub_path));
+            } else {
+                try std.testing.expect(!try realpathMatches(tmp.dir, sub_path));
+            }
+        }
+    }
+}
+
+fn realpathMatches(dir: std.fs.Dir, sub_path: []const u8) !bool {
+    var real_path_buf: [std.fs.max_path_bytes]u8 = undefined;
+    const real_path = try dir.realpath(sub_path, &real_path_buf);
+    var sub_path_it = try std.fs.path.NativeComponentIterator.init(sub_path);
+    var real_path_it = std.fs.path.NativeComponentIterator.init(real_path) catch unreachable;
+    sub_path_it.moveToEnd();
+    real_path_it.moveToEnd();
+    var match = true;
+    while (true) {
+        const sub_path_component = sub_path_it.previous() orelse break;
+        const real_path_component = real_path_it.previous() orelse unreachable;
+        std.debug.assert(std.ascii.eqlIgnoreCase(sub_path_component.name, real_path_component.name));
+        match = match and std.mem.eql(u8, sub_path_component.name, real_path_component.name);
+    }
+    return match;
+}
+
+fn testIsFilesystemCaseSensitive(test_dir: std.fs.Dir) !bool {
+    const name_lower = "case-sensitivity-test-file";
+    const name_upper = "CASE-SENSITIVITY-TEST-FILE";
+
+    test_dir.deleteFile(name_lower) catch |err| switch (err) {
+        error.FileNotFound => {},
+        else => |e| return e,
+    };
+    test_dir.deleteFile(name_upper) catch |err| switch (err) {
+        error.FileNotFound => {},
+        else => |e| return e,
+    };
+
+    {
+        const file = try test_dir.createFile(name_lower, .{});
+        file.close();
+    }
+    defer test_dir.deleteFile(name_lower) catch |err| std.debug.panic(
+        "failed to delete test file '{s}' with {s}\n",
+        .{ name_lower, @errorName(err) },
+    );
+    {
+        const file = test_dir.openFile(name_upper, .{}) catch |err| switch (err) {
+            error.FileNotFound => return true,
+            else => |e| return e,
+        };
+        file.close();
+    }
+    return false;
+}

src/Sema.zig

@@ -14047,6 +14047,9 @@ fn zirImport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
     const operand = sema.code.nullTerminatedString(extra.path);
 
     const result = pt.importFile(block.getFileScope(zcu), operand) catch |err| switch (err) {
+        error.ImportCaseMismatch => {
+            return sema.fail(block, operand_src, "import string '{s}' case does not match the filename", .{operand});
+        },
         error.ImportOutsideModulePath => {
             return sema.fail(block, operand_src, "import of file outside module path: '{s}'", .{operand});
         },
@@ -14109,6 +14112,9 @@ fn zirEmbedFile(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!A
     }
 
     const ef_idx = pt.embedFile(block.getFileScope(zcu), name) catch |err| switch (err) {
+        error.ImportCaseMismatch => {
+            return sema.fail(block, operand_src, "embed string '{s}' case does not match the filename", .{name});
+        },
         error.ImportOutsideModulePath => {
             return sema.fail(block, operand_src, "embed of file outside package path: '{s}'", .{name});
         },

src/Zcu/PerThread.zig

@@ -1950,6 +1950,70 @@ pub fn importPkg(pt: Zcu.PerThread, mod: *Module) Allocator.Error!Zcu.ImportFile
     };
 }
 
+fn eqlIgnoreCase(a: []const u8, b: []const u8) bool {
+    if (builtin.os.tag == .windows)
+        return std.os.windows.eqlIgnoreCaseWtf8(a, b);
+
+    var a_utf8_it = std.unicode.Utf8View.initUnchecked(a).iterator();
+    var b_utf8_it = std.unicode.Utf8View.initUnchecked(b).iterator();
+    while (true) {
+        const a_cp = a_utf8_it.nextCodepoint() orelse break;
+        const b_cp = b_utf8_it.nextCodepoint() orelse return false;
+        if (a_cp != b_cp) {
+            const a_upper = std.ascii.toUpper(std.math.cast(u8, a_cp) orelse return false);
+            const b_upper = std.ascii.toUpper(std.math.cast(u8, b_cp) orelse return false);
+            if (a_upper != b_upper)
+                return false;
+        }
+    }
+    if (b_utf8_it.nextCodepoint() != null) return false;
+
+    return true;
+}
+
+fn previousResolveDots(it: *std.fs.path.NativeComponentIterator) ?std.fs.path.NativeComponentIterator.Component {
+    var dot_dot_count: usize = 0;
+    while (true) {
+        const component = it.previous() orelse return null;
+        if (std.mem.eql(u8, component.name, ".")) {
+            // ignore
+        } else if (std.mem.eql(u8, component.name, "..")) {
+            dot_dot_count += 1;
+        } else {
+            if (dot_dot_count == 0) return component;
+            dot_dot_count -= 1;
+        }
+    }
+}
+
+fn checkImportCase(path: Cache.Path, sub_path: []const u8, import_string: []const u8) enum { ok, mismatch } {
+    // disabled on wasi because realpath is not implemented
+    if (builtin.os.tag == .wasi) return .ok;
+
+    var import_it = std.fs.path.NativeComponentIterator.init(import_string) catch return .ok;
+    import_it.moveToEnd();
+
+    var real_path_buf: [std.fs.max_path_bytes]u8 = undefined;
+    const real_path = path.realpath(sub_path, &real_path_buf) catch |err| switch (err) {
+        error.FileNotFound => return .ok,
+        else => |e| std.debug.panic("realpath '{}{s}' failed with {s}", .{ path, sub_path, @errorName(e) }),
+    };
+    var real_path_it = std.fs.path.NativeComponentIterator.init(real_path) catch unreachable;
+    real_path_it.moveToEnd();
+
+    var match = true;
+    while (true) {
+        const import_component = previousResolveDots(&import_it) orelse break;
+        const real_path_component = previousResolveDots(&real_path_it) orelse unreachable;
+        if (!eqlIgnoreCase(import_component.name, real_path_component.name)) {
+            std.debug.panic("real path '{s}' does not end with import path '{s}'", .{ real_path, import_string });
+        }
+        match = match and std.mem.eql(u8, import_component.name, real_path_component.name);
+    }
+
+    return if (match) .ok else .mismatch;
+}
+
 /// Called from a worker thread during AstGen (with the Compilation mutex held).
 /// Also called from Sema during semantic analysis.
 /// Does not attempt to load the file from disk; just returns a corresponding `*Zcu.File`.
@@ -1960,6 +2024,7 @@ pub fn importFile(
 ) error{
     OutOfMemory,
     ModuleNotFound,
+    ImportCaseMismatch,
     ImportOutsideModulePath,
     CurrentWorkingDirectoryUnlinked,
 }!Zcu.ImportFileResult {
@@ -1993,6 +2058,15 @@ pub fn importFile(
         import_string,
     });
 
+    {
+        const relative_path = try std.fs.path.resolve(gpa, &.{ cur_file.sub_file_path, "..", import_string });
+        defer gpa.free(relative_path);
+        switch (checkImportCase(mod.root, relative_path, import_string)) {
+            .ok => {},
+            .mismatch => return error.ImportCaseMismatch,
+        }
+    }
+
     var keep_resolved_path = false;
     defer if (!keep_resolved_path) gpa.free(resolved_path);
 
@@ -2077,6 +2151,7 @@ pub fn embedFile(
     import_string: []const u8,
 ) error{
     OutOfMemory,
+    ImportCaseMismatch,
     ImportOutsideModulePath,
     CurrentWorkingDirectoryUnlinked,
 }!Zcu.EmbedFile.Index {
@@ -2114,6 +2189,15 @@ pub fn embedFile(
     });
     errdefer gpa.free(resolved_path);
 
+    {
+        const relative_path = try std.fs.path.resolve(gpa, &.{ cur_file.sub_file_path, "..", import_string });
+        defer gpa.free(relative_path);
+        switch (checkImportCase(cur_file.mod.root, relative_path, import_string)) {
+            .ok => {},
+            .mismatch => return error.ImportCaseMismatch,
+        }
+    }
+
     const gop = try zcu.embed_table.getOrPut(gpa, resolved_path);
     errdefer assert(std.mem.eql(u8, zcu.embed_table.pop().?.key, resolved_path));
 

test/standalone/build.zig.zon

@@ -189,6 +189,9 @@
         .config_header = .{
             .path = "config_header",
         },
+        .case_sensitivity = .{
+            .path = "case_sensitivity",
+        },
     },
     .paths = .{
         "build.zig",

test/standalone/case_sensitivity/build.zig

@@ -0,0 +1,75 @@
+const builtin = @import("builtin");
+const std = @import("std");
+
+pub fn build(b: *std.Build) !void {
+    const fs_case_sensitive = try isFilesystemCaseSensitive(b.build_root);
+    switch (builtin.os.tag) {
+        .windows, .macos => try std.testing.expectEqual(false, fs_case_sensitive),
+        else => {},
+    }
+    addCase(b, fs_case_sensitive, .import, .good);
+    addCase(b, fs_case_sensitive, .import, .bad);
+    addCase(b, fs_case_sensitive, .embed, .good);
+    addCase(b, fs_case_sensitive, .embed, .bad);
+}
+
+fn addCase(
+    b: *std.Build,
+    fs_case_sensitive: bool,
+    comptime kind: enum { import, embed },
+    comptime variant: enum { good, bad },
+) void {
+    const name = @tagName(kind) ++ @tagName(variant);
+    const compile = b.addSystemCommand(&.{
+        b.graph.zig_exe,
+        "build-exe",
+        "-fno-emit-bin",
+        name ++ ".zig",
+    });
+    if (variant == .bad) {
+        if (fs_case_sensitive) {
+            switch (kind) {
+                .import => compile.addCheck(.{ .expect_stderr_match = "unable to load" }),
+                .embed => compile.addCheck(.{ .expect_stderr_match = "unable to open" }),
+            }
+            compile.addCheck(.{ .expect_stderr_match = "Foo.zig" });
+            compile.addCheck(.{ .expect_stderr_match = "FileNotFound" });
+        } else {
+            compile.addCheck(.{
+                .expect_stderr_match = b.fmt("{s} string 'Foo.zig' case does not match the filename", .{@tagName(kind)}),
+            });
+        }
+    }
+    b.default_step.dependOn(&compile.step);
+}
+
+fn isFilesystemCaseSensitive(test_dir: std.Build.Cache.Directory) !bool {
+    const name_lower = "case-sensitivity-test-file";
+    const name_upper = "CASE-SENSITIVITY-TEST-FILE";
+
+    test_dir.handle.deleteFile(name_lower) catch |err| switch (err) {
+        error.FileNotFound => {},
+        else => |e| return e,
+    };
+    test_dir.handle.deleteFile(name_upper) catch |err| switch (err) {
+        error.FileNotFound => {},
+        else => |e| return e,
+    };
+
+    {
+        const file = try test_dir.handle.createFile(name_lower, .{});
+        file.close();
+    }
+    defer test_dir.handle.deleteFile(name_lower) catch |err| std.debug.panic(
+        "failed to delete test file '{s}' in directory '{}' with {s}\n",
+        .{ name_lower, test_dir, @errorName(err) },
+    );
+    {
+        const file = test_dir.handle.openFile(name_upper, .{}) catch |err| switch (err) {
+            error.FileNotFound => return true,
+            else => |e| return e,
+        };
+        file.close();
+    }
+    return false;
+}

test/standalone/case_sensitivity/embedbad.zig

@@ -0,0 +1,3 @@
+pub fn main() u8 {
+    return @embedFile("Foo.zig").len;
+}

test/standalone/case_sensitivity/embedgood.zig

@@ -0,0 +1,3 @@
+pub fn main() u8 {
+    return @embedFile("foo.zig").len;
+}

test/standalone/case_sensitivity/foo.zig

@@ -0,0 +1 @@
+pub const value = 42;

test/standalone/case_sensitivity/importbad.zig

@@ -0,0 +1,3 @@
+pub fn main() u8 {
+    return @import("Foo.zig").value;
+}

test/standalone/case_sensitivity/importgood.zig

@@ -0,0 +1,3 @@
+pub fn main() u8 {
+    return @import("foo.zig").value;
+}