config: store some basic errors on parse

src/cli_args.zig

@@ -4,10 +4,20 @@ const assert = std.debug.assert;
 const Allocator = mem.Allocator;
 const ArenaAllocator = std.heap.ArenaAllocator;
 
+const ErrorList = @import("config/ErrorList.zig");
+
 // TODO:
 //   - Only `--long=value` format is accepted. Do we want to allow
 //     `--long value`? Not currently allowed.
 
+/// The base errors for arg parsing. Additional errors can be returned due
+/// to type-specific parsing but these are always possible.
+pub const Error = error{
+    ValueRequired,
+    InvalidField,
+    InvalidValue,
+};
+
 /// Parse the command line arguments from iter into dst.
 ///
 /// dst must be a struct. The fields and their types will be used to determine
@@ -19,6 +29,10 @@ const ArenaAllocator = std.heap.ArenaAllocator;
 /// an arena allocator will be created (or reused if set already) for any
 /// allocations. Allocations are necessary for certain types, like `[]const u8`.
 ///
+/// If the destination type has a field "_errors" of type "ErrorList" then
+/// errors will be added to that list. In this case, the only error returned by
+/// parse are allocation errors.
+///
 /// Note: If the arena is already non-null, then it will be used. In this
 /// case, in the case of an error some memory might be leaked into the arena.
 pub fn parse(comptime T: type, alloc: Allocator, dst: *T, iter: anytype) !void {
@@ -62,11 +76,45 @@ pub fn parse(comptime T: type, alloc: Allocator, dst: *T, iter: anytype) !void {
                 break :value null;
             };
 
-            try parseIntoField(T, arena_alloc, dst, key, value);
+            parseIntoField(T, arena_alloc, dst, key, value) catch |err| {
+                if (comptime !canTrackErrors(T)) return err;
+                switch (err) {
+                    error.InvalidField => try dst._errors.add(arena_alloc, .{
+                        .message = try std.fmt.allocPrintZ(
+                            arena_alloc,
+                            "unknown field: {s}",
+                            .{key},
+                        ),
+                    }),
+
+                    error.ValueRequired => try dst._errors.add(arena_alloc, .{
+                        .message = try std.fmt.allocPrintZ(
+                            arena_alloc,
+                            "{s}: value required",
+                            .{key},
+                        ),
+                    }),
+
+                    error.InvalidValue => try dst._errors.add(arena_alloc, .{
+                        .message = try std.fmt.allocPrintZ(
+                            arena_alloc,
+                            "{s}: invalid value",
+                            .{key},
+                        ),
+                    }),
+
+                    else => return err,
+                }
+            };
         }
     }
 }
 
+/// Returns true if this type can track errors.
+fn canTrackErrors(comptime T: type) bool {
+    return @hasField(T, "_errors");
+}
+
 /// Parse a single key/value pair into the destination type T.
 ///
 /// This may result in allocations. The allocations can only be freed by freeing
@@ -240,6 +288,29 @@ test "parse: quoted value" {
     try testing.expectEqualStrings("hello!", data.b);
 }
 
+test "parse: error tracking" {
+    const testing = std.testing;
+
+    var data: struct {
+        a: []const u8 = "",
+        b: enum { one } = .one,
+
+        _arena: ?ArenaAllocator = null,
+        _errors: ErrorList = .{},
+    } = .{};
+    defer if (data._arena) |arena| arena.deinit();
+
+    var iter = try std.process.ArgIteratorGeneral(.{}).init(
+        testing.allocator,
+        "--what --a=42",
+    );
+    defer iter.deinit();
+    try parse(@TypeOf(data), testing.allocator, &data, &iter);
+    try testing.expect(data._arena != null);
+    try testing.expectEqualStrings("42", data.a);
+    try testing.expect(!data._errors.empty());
+}
+
 test "parseIntoField: ignore underscore-prefixed fields" {
     const testing = std.testing;
     var arena = ArenaAllocator.init(testing.allocator);

src/config/Config.zig

@@ -14,6 +14,7 @@ const cli_args = @import("../cli_args.zig");
 
 const Key = @import("key.zig").Key;
 const KeyValue = @import("key.zig").Value;
+const ErrorList = @import("ErrorList.zig");
 
 const log = std.log.scoped(.config);
 
@@ -341,6 +342,11 @@ keybind: Keybinds = .{},
 /// This is set by the CLI parser for deinit.
 _arena: ?ArenaAllocator = null,
 
+/// List of errors that occurred while loading. This can be accessed directly
+/// by callers. It is only underscore-prefixed so it can't be set by the
+/// configuration file.
+_errors: ErrorList = .{},
+
 pub fn deinit(self: *Config) void {
     if (self._arena) |arena| arena.deinit();
     self.* = undefined;

src/input/Binding.zig

@@ -393,7 +393,7 @@ pub const Set = struct {
         alloc: Allocator,
         t: Trigger,
         action: Action,
-    ) !void {
+    ) Allocator.Error!void {
         // unbind should never go into the set, it should be handled prior
         assert(action != .unbind);