Merge branch 'daurnimator-less-buffer'

Closes #4405
Closes #4656

8 files changed, 159 insertions, 119 deletions

diff --git a/lib/std/array_list.zig b/lib/std/array_list.zig
index d1946be02a..cbbec0b4f3 100644
--- a/lib/std/array_list.zig
+++ b/lib/std/array_list.zig
@@ -5,10 +5,8 @@ const testing = std.testing;
 const mem = std.mem;
 const Allocator = mem.Allocator;
 
-/// List of items.
-///
-/// This is a wrapper around an array of T values. Initialize with
-/// `init`.
+/// A contiguous, growable list of items in memory.
+/// This is a wrapper around an array of T values. Initialize with `init`.
 pub fn ArrayList(comptime T: type) type {
     return AlignedArrayList(T, null);
 }
@@ -22,7 +20,7 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
     return struct {
         const Self = @This();
 
-        /// Use toSlice instead of slicing this directly, because if you don't
+        /// Use `span` instead of slicing this directly, because if you don't
         /// specify the end position of the slice, this will potentially give
         /// you uninitialized memory.
         items: Slice,
@@ -56,34 +54,37 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
 
         /// Return contents as a slice. Only valid while the list
         /// doesn't change size.
-        pub fn toSlice(self: Self) Slice {
+        pub fn span(self: var) @TypeOf(self.items[0..self.len]) {
             return self.items[0..self.len];
         }
 
-        /// Return list as const slice. Only valid while the list
-        /// doesn't change size.
+        /// Deprecated: use `span`.
+        pub fn toSlice(self: Self) Slice {
+            return self.span();
+        }
+
+        /// Deprecated: use `span`.
         pub fn toSliceConst(self: Self) SliceConst {
-            return self.items[0..self.len];
+            return self.span();
         }
 
-        /// Safely access index i of the list.
+        /// Deprecated: use `span()[i]`.
         pub fn at(self: Self, i: usize) T {
-            return self.toSliceConst()[i];
+            return self.span()[i];
         }
 
-        /// Safely access ptr to index i of the list.
+        /// Deprecated: use `&span()[i]`.
         pub fn ptrAt(self: Self, i: usize) *T {
-            return &self.toSlice()[i];
+            return &self.span()[i];
         }
 
-        /// Sets the value at index `i`, or returns `error.OutOfBounds` if
-        /// the index is not in range.
+        /// Deprecated: use `if (i >= list.len) return error.OutOfBounds else span()[i] = item`.
         pub fn setOrError(self: Self, i: usize, item: T) !void {
             if (i >= self.len) return error.OutOfBounds;
             self.items[i] = item;
         }
 
-        /// Sets the value at index `i`, asserting that the value is in range.
+        /// Deprecated: use `list.span()[i] = item`.
         pub fn set(self: *Self, i: usize, item: T) void {
             assert(i < self.len);
             self.items[i] = item;
@@ -124,18 +125,18 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
             self.items[n] = item;
         }
 
-        /// Insert slice `items` at index `n`. Moves
-        /// `list[n .. list.len]` to make room.
-        pub fn insertSlice(self: *Self, n: usize, items: SliceConst) !void {
+        /// Insert slice `items` at index `i`. Moves
+        /// `list[i .. list.len]` to make room.
+        /// This operation is O(N).
+        pub fn insertSlice(self: *Self, i: usize, items: SliceConst) !void {
             try self.ensureCapacity(self.len + items.len);
             self.len += items.len;
 
-            mem.copyBackwards(T, self.items[n + items.len .. self.len], self.items[n .. self.len - items.len]);
-            mem.copy(T, self.items[n .. n + items.len], items);
+            mem.copyBackwards(T, self.items[i + items.len .. self.len], self.items[i .. self.len - items.len]);
+            mem.copy(T, self.items[i .. i + items.len], items);
         }
 
-        /// Extend the list by 1 element. Allocates more memory as
-        /// necessary.
+        /// Extend the list by 1 element. Allocates more memory as necessary.
         pub fn append(self: *Self, item: T) !void {
             const new_item_ptr = try self.addOne();
             new_item_ptr.* = item;
@@ -148,8 +149,9 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
             new_item_ptr.* = item;
         }
 
-        /// Remove the element at index `i` from the list and return
-        /// its value. Asserts the array has at least one item.
+        /// Remove the element at index `i` from the list and return its value.
+        /// Asserts the array has at least one item.
+        /// This operation is O(N).
         pub fn orderedRemove(self: *Self, i: usize) T {
             const newlen = self.len - 1;
             if (newlen == i) return self.pop();
@@ -163,18 +165,17 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
 
         /// Removes the element at the specified index and returns it.
         /// The empty slot is filled from the end of the list.
+        /// This operation is O(1).
         pub fn swapRemove(self: *Self, i: usize) T {
             if (self.len - 1 == i) return self.pop();
 
-            const slice = self.toSlice();
+            const slice = self.span();
             const old_item = slice[i];
             slice[i] = self.pop();
             return old_item;
         }
 
-        /// Removes the element at the specified index and returns it
-        /// or an error.OutOfBounds is returned. If no error then
-        /// the empty slot is filled from the end of the list.
+        /// Deprecated: use `if (i >= list.len) return error.OutOfBounds else list.swapRemove(i)`.
         pub fn swapRemoveOrError(self: *Self, i: usize) !T {
             if (i >= self.len) return error.OutOfBounds;
             return self.swapRemove(i);
@@ -204,6 +205,7 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
         }
 
         /// Reduce allocated capacity to `new_len`.
+        /// Invalidates element pointers.
         pub fn shrink(self: *Self, new_len: usize) void {
             assert(new_len <= self.len);
             self.len = new_len;
@@ -222,13 +224,24 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
             self.items = try self.allocator.realloc(self.items, better_capacity);
         }
 
+        /// Increases the array's length to match the full capacity that is already allocated.
+        /// The new elements have `undefined` values. This operation does not invalidate any
+        /// element pointers.
+        pub fn expandToCapacity(self: *Self) void {
+            self.len = self.items.len;
+        }
+
         /// Increase length by 1, returning pointer to the new item.
+        /// The returned pointer becomes invalid when the list is resized.
         pub fn addOne(self: *Self) !*T {
             const new_length = self.len + 1;
             try self.ensureCapacity(new_length);
             return self.addOneAssumeCapacity();
         }
 
+        /// Increase length by 1, returning pointer to the new item.
+        /// Asserts that there is already space for the new item without allocating more.
+        /// The returned pointer becomes invalid when the list is resized.
         pub fn addOneAssumeCapacity(self: *Self) *T {
             assert(self.len < self.capacity());
             const result = &self.items[self.len];
@@ -236,14 +249,15 @@ pub fn AlignedArrayList(comptime T: type, comptime alignment: ?u29) type {
             return result;
         }
 
-        /// Remove and return the last element from the list. Asserts
-        /// the list has at least one item.
+        /// Remove and return the last element from the list.
+        /// Asserts the list has at least one item.
         pub fn pop(self: *Self) T {
             self.len -= 1;
             return self.items[self.len];
         }
 
-        /// Like `pop` but returns `null` if empty.
+        /// Remove and return the last element from the list.
+        /// If the list is empty, returns `null`.
         pub fn popOrNull(self: *Self) ?T {
             if (self.len == 0) return null;
             return self.pop();
@@ -287,7 +301,7 @@ test "std.ArrayList.basic" {
         }
     }
 
-    for (list.toSlice()) |v, i| {
+    for (list.span()) |v, i| {
         testing.expect(v == @intCast(i32, i + 1));
     }
 
@@ -325,7 +339,7 @@ test "std.ArrayList.appendNTimes" {
 
     try list.appendNTimes(2, 10);
     testing.expectEqual(@as(usize, 10), list.len);
-    for (list.toSlice()) |element| {
+    for (list.span()) |element| {
         testing.expectEqual(@as(i32, 2), element);
     }
 }
diff --git a/lib/std/buffer.zig b/lib/std/buffer.zig
index f808af1485..9bf024191e 100644
--- a/lib/std/buffer.zig
+++ b/lib/std/buffer.zig
@@ -81,12 +81,18 @@ pub const Buffer = struct {
         self.list.deinit();
     }
 
+    pub fn span(self: var) @TypeOf(self.list.items[0 .. self.list.len - 1 :0]) {
+        return self.list.span()[0..self.len() :0];
+    }
+
+    /// Deprecated: use `span`
     pub fn toSlice(self: Buffer) [:0]u8 {
-        return self.list.toSlice()[0..self.len() :0];
+        return self.span();
     }
 
+    /// Deprecated: use `span`
     pub fn toSliceConst(self: Buffer) [:0]const u8 {
-        return self.list.toSliceConst()[0..self.len() :0];
+        return self.span();
     }
 
     pub fn shrink(self: *Buffer, new_len: usize) void {
diff --git a/lib/std/build.zig b/lib/std/build.zig
index 59e6c4e87c..bc8b8acba0 100644
--- a/lib/std/build.zig
+++ b/lib/std/build.zig
@@ -926,11 +926,9 @@ pub const Builder = struct {
 
         try child.spawn();
 
-        var stdout = std.Buffer.initNull(self.allocator);
-        defer std.Buffer.deinit(&stdout);
-
         var stdout_file_in_stream = child.stdout.?.inStream();
-        try stdout_file_in_stream.stream.readAllBuffer(&stdout, max_output_size);
+        const stdout = try stdout_file_in_stream.stream.readAllAlloc(self.allocator, max_output_size);
+        errdefer self.allocator.free(stdout);
 
         const term = try child.wait();
         switch (term) {
@@ -939,7 +937,7 @@ pub const Builder = struct {
                     out_code.* = @truncate(u8, code);
                     return error.ExitCodeFailure;
                 }
-                return stdout.toOwnedSlice();
+                return stdout;
             },
             .Signal, .Stopped, .Unknown => |code| {
                 out_code.* = @truncate(u8, code);
diff --git a/lib/std/build/run.zig b/lib/std/build/run.zig
index eacf408ba9..41417572ca 100644
--- a/lib/std/build/run.zig
+++ b/lib/std/build/run.zig
@@ -9,7 +9,6 @@ const mem = std.mem;
 const process = std.process;
 const ArrayList = std.ArrayList;
 const BufMap = std.BufMap;
-const Buffer = std.Buffer;
 const warn = std.debug.warn;
 
 const max_stdout_size = 1 * 1024 * 1024; // 1 MiB
@@ -169,23 +168,26 @@ pub const RunStep = struct {
             return err;
         };
 
-        var stdout = Buffer.initNull(self.builder.allocator);
-        var stderr = Buffer.initNull(self.builder.allocator);
-
         // TODO need to poll to read these streams to prevent a deadlock (or rely on evented I/O).
 
+        var stdout: ?[]const u8 = null;
+        defer if (stdout) |s| self.builder.allocator.free(s);
+
         switch (self.stdout_action) {
             .expect_exact, .expect_matches => {
                 var stdout_file_in_stream = child.stdout.?.inStream();
-                stdout_file_in_stream.stream.readAllBuffer(&stdout, max_stdout_size) catch unreachable;
+                stdout = stdout_file_in_stream.stream.readAllAlloc(self.builder.allocator, max_stdout_size) catch unreachable;
             },
             .inherit, .ignore => {},
         }
 
-        switch (self.stdout_action) {
+        var stderr: ?[]const u8 = null;
+        defer if (stderr) |s| self.builder.allocator.free(s);
+
+        switch (self.stderr_action) {
             .expect_exact, .expect_matches => {
                 var stderr_file_in_stream = child.stderr.?.inStream();
-                stderr_file_in_stream.stream.readAllBuffer(&stderr, max_stdout_size) catch unreachable;
+                stderr = stderr_file_in_stream.stream.readAllAlloc(self.builder.allocator, max_stdout_size) catch unreachable;
             },
             .inherit, .ignore => {},
         }
@@ -216,7 +218,7 @@ pub const RunStep = struct {
         switch (self.stderr_action) {
             .inherit, .ignore => {},
             .expect_exact => |expected_bytes| {
-                if (!mem.eql(u8, expected_bytes, stderr.toSliceConst())) {
+                if (!mem.eql(u8, expected_bytes, stderr.?)) {
                     warn(
                         \\
                         \\========= Expected this stderr: =========
@@ -224,13 +226,13 @@ pub const RunStep = struct {
                         \\========= But found: ====================
                         \\{}
                         \\
-                    , .{ expected_bytes, stderr.toSliceConst() });
+                    , .{ expected_bytes, stderr.? });
                     printCmd(cwd, argv);
                     return error.TestFailed;
                 }
             },
             .expect_matches => |matches| for (matches) |match| {
-                if (mem.indexOf(u8, stderr.toSliceConst(), match) == null) {
+                if (mem.indexOf(u8, stderr.?, match) == null) {
                     warn(
                         \\
                         \\========= Expected to find in stderr: =========
@@ -238,7 +240,7 @@ pub const RunStep = struct {
                         \\========= But stderr does not contain it: =====
                         \\{}
                         \\
-                    , .{ match, stderr.toSliceConst() });
+                    , .{ match, stderr.? });
                     printCmd(cwd, argv);
                     return error.TestFailed;
                 }
@@ -248,7 +250,7 @@ pub const RunStep = struct {
         switch (self.stdout_action) {
             .inherit, .ignore => {},
             .expect_exact => |expected_bytes| {
-                if (!mem.eql(u8, expected_bytes, stdout.toSliceConst())) {
+                if (!mem.eql(u8, expected_bytes, stdout.?)) {
                     warn(
                         \\
                         \\========= Expected this stdout: =========
@@ -256,13 +258,13 @@ pub const RunStep = struct {
                         \\========= But found: ====================
                         \\{}
                         \\
-                    , .{ expected_bytes, stdout.toSliceConst() });
+                    , .{ expected_bytes, stdout.? });
                     printCmd(cwd, argv);
                     return error.TestFailed;
                 }
             },
             .expect_matches => |matches| for (matches) |match| {
-                if (mem.indexOf(u8, stdout.toSliceConst(), match) == null) {
+                if (mem.indexOf(u8, stdout.?, match) == null) {
                     warn(
                         \\
                         \\========= Expected to find in stdout: =========
@@ -270,7 +272,7 @@ pub const RunStep = struct {
                         \\========= But stdout does not contain it: =====
                         \\{}
                         \\
-                    , .{ match, stdout.toSliceConst() });
+                    , .{ match, stdout.? });
                     printCmd(cwd, argv);
                     return error.TestFailed;
                 }
diff --git a/lib/std/child_process.zig b/lib/std/child_process.zig
index d5e914b286..4f5fc2b496 100644
--- a/lib/std/child_process.zig
+++ b/lib/std/child_process.zig
@@ -217,21 +217,19 @@ pub const ChildProcess = struct {
 
         try child.spawn();
 
-        var stdout = Buffer.initNull(args.allocator);
-        var stderr = Buffer.initNull(args.allocator);
-        defer Buffer.deinit(&stdout);
-        defer Buffer.deinit(&stderr);
-
         var stdout_file_in_stream = child.stdout.?.inStream();
         var stderr_file_in_stream = child.stderr.?.inStream();
 
-        try stdout_file_in_stream.stream.readAllBuffer(&stdout, args.max_output_bytes);
-        try stderr_file_in_stream.stream.readAllBuffer(&stderr, args.max_output_bytes);
+        // TODO need to poll to read these streams to prevent a deadlock (or rely on evented I/O).
+        const stdout = try stdout_file_in_stream.stream.readAllAlloc(args.allocator, args.max_output_bytes);
+        errdefer args.allocator.free(stdout);
+        const stderr = try stderr_file_in_stream.stream.readAllAlloc(args.allocator, args.max_output_bytes);
+        errdefer args.allocator.free(stderr);
 
         return ExecResult{
             .term = try child.wait(),
-            .stdout = stdout.toOwnedSlice(),
-            .stderr = stderr.toOwnedSlice(),
+            .stdout = stdout,
+            .stderr = stderr,
         };
     }
 
diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index 9b35e56e5a..deae0a717b 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -1643,10 +1643,10 @@ test "hexToBytes" {
 test "formatIntValue with comptime_int" {
     const value: comptime_int = 123456789123456789;
 
-    var buf = try std.Buffer.init(std.testing.allocator, "");
+    var buf = std.ArrayList(u8).init(std.testing.allocator);
     defer buf.deinit();
-    try formatIntValue(value, "", FormatOptions{}, &buf, @TypeOf(std.Buffer.append).ReturnType.ErrorSet, std.Buffer.append);
-    std.testing.expect(mem.eql(u8, buf.toSlice(), "123456789123456789"));
+    try formatIntValue(value, "", FormatOptions{}, &buf, @TypeOf(std.ArrayList(u8).appendSlice).ReturnType.ErrorSet, std.ArrayList(u8).appendSlice);
+    std.testing.expect(mem.eql(u8, buf.toSliceConst(), "123456789123456789"));
 }
 
 test "formatType max_depth" {
@@ -1698,24 +1698,24 @@ test "formatType max_depth" {
     inst.a = &inst;
     inst.tu.ptr = &inst.tu;
 
-    var buf0 = try std.Buffer.init(std.testing.allocator, "");
+    var buf0 = std.ArrayList(u8).init(std.testing.allocator);
     defer buf0.deinit();
-    try formatType(inst, "", FormatOptions{}, &buf0, @TypeOf(std.Buffer.append).ReturnType.ErrorSet, std.Buffer.append, 0);
+    try formatType(inst, "", FormatOptions{}, &buf0, @TypeOf(std.ArrayList(u8).appendSlice).ReturnType.ErrorSet, std.ArrayList(u8).appendSlice, 0);
     std.testing.expect(mem.eql(u8, buf0.toSlice(), "S{ ... }"));
 
-    var buf1 = try std.Buffer.init(std.testing.allocator, "");
+    var buf1 = std.ArrayList(u8).init(std.testing.allocator);
     defer buf1.deinit();
-    try formatType(inst, "", FormatOptions{}, &buf1, @TypeOf(std.Buffer.append).ReturnType.ErrorSet, std.Buffer.append, 1);
+    try formatType(inst, "", FormatOptions{}, &buf1, @TypeOf(std.ArrayList(u8).appendSlice).ReturnType.ErrorSet, std.ArrayList(u8).appendSlice, 1);
     std.testing.expect(mem.eql(u8, buf1.toSlice(), "S{ .a = S{ ... }, .tu = TU{ ... }, .e = E.Two, .vec = (10.200,2.220) }"));
 
-    var buf2 = try std.Buffer.init(std.testing.allocator, "");
+    var buf2 = std.ArrayList(u8).init(std.testing.allocator);
     defer buf2.deinit();
-    try formatType(inst, "", FormatOptions{}, &buf2, @TypeOf(std.Buffer.append).ReturnType.ErrorSet, std.Buffer.append, 2);
+    try formatType(inst, "", FormatOptions{}, &buf2, @TypeOf(std.ArrayList(u8).appendSlice).ReturnType.ErrorSet, std.ArrayList(u8).appendSlice, 2);
     std.testing.expect(mem.eql(u8, buf2.toSlice(), "S{ .a = S{ .a = S{ ... }, .tu = TU{ ... }, .e = E.Two, .vec = (10.200,2.220) }, .tu = TU{ .ptr = TU{ ... } }, .e = E.Two, .vec = (10.200,2.220) }"));
 
-    var buf3 = try std.Buffer.init(std.testing.allocator, "");
+    var buf3 = std.ArrayList(u8).init(std.testing.allocator);
     defer buf3.deinit();
-    try formatType(inst, "", FormatOptions{}, &buf3, @TypeOf(std.Buffer.append).ReturnType.ErrorSet, std.Buffer.append, 3);
+    try formatType(inst, "", FormatOptions{}, &buf3, @TypeOf(std.ArrayList(u8).appendSlice).ReturnType.ErrorSet, std.ArrayList(u8).appendSlice, 3);
     std.testing.expect(mem.eql(u8, buf3.toSlice(), "S{ .a = S{ .a = S{ .a = S{ ... }, .tu = TU{ ... }, .e = E.Two, .vec = (10.200,2.220) }, .tu = TU{ .ptr = TU{ ... } }, .e = E.Two, .vec = (10.200,2.220) }, .tu = TU{ .ptr = TU{ .ptr = TU{ ... } } }, .e = E.Two, .vec = (10.200,2.220) }"));
 }
 
diff --git a/lib/std/io/in_stream.zig b/lib/std/io/in_stream.zig
index 4f3bac3c21..e234182771 100644
--- a/lib/std/io/in_stream.zig
+++ b/lib/std/io/in_stream.zig
@@ -41,10 +41,13 @@ pub fn InStream(comptime ReadError: type) type {
             }
         }
 
+        /// Deprecated: use `readAll`.
+        pub const readFull = readAll;
+
         /// Returns the number of bytes read. If the number read is smaller than buf.len, it
         /// means the stream reached the end. Reaching the end of a stream is not an error
         /// condition.
-        pub fn readFull(self: *Self, buffer: []u8) Error!usize {
+        pub fn readAll(self: *Self, buffer: []u8) Error!usize {
             var index: usize = 0;
             while (index != buffer.len) {
                 const amt = try self.read(buffer[index..]);
@@ -57,30 +60,43 @@ pub fn InStream(comptime ReadError: type) type {
         /// Returns the number of bytes read. If the number read would be smaller than buf.len,
         /// error.EndOfStream is returned instead.
         pub fn readNoEof(self: *Self, buf: []u8) !void {
-            const amt_read = try self.readFull(buf);
+            const amt_read = try self.readAll(buf);
             if (amt_read < buf.len) return error.EndOfStream;
         }
 
-        /// Replaces `buffer` contents by reading from the stream until it is finished.
-        /// If `buffer.len()` would exceed `max_size`, `error.StreamTooLong` is returned and
-        /// the contents read from the stream are lost.
+        /// Deprecated: use `readAllArrayList`.
         pub fn readAllBuffer(self: *Self, buffer: *Buffer, max_size: usize) !void {
-            try buffer.resize(0);
+            buffer.list.shrink(0);
+            try self.readAllArrayList(&buffer.list, max_size);
+            errdefer buffer.shrink(0);
+            try buffer.list.append(0);
+        }
 
-            var actual_buf_len: usize = 0;
+        /// Appends to the `std.ArrayList` contents by reading from the stream until end of stream is found.
+        /// If the number of bytes appended would exceed `max_append_size`, `error.StreamTooLong` is returned
+        /// and the `std.ArrayList` has exactly `max_append_size` bytes appended.
+        pub fn readAllArrayList(self: *Self, array_list: *std.ArrayList(u8), max_append_size: usize) !void {
+            try array_list.ensureCapacity(math.min(max_append_size, 4096));
+            const original_len = array_list.len;
+            var start_index: usize = original_len;
             while (true) {
-                const dest_slice = buffer.toSlice()[actual_buf_len..];
-                const bytes_read = try self.readFull(dest_slice);
-                actual_buf_len += bytes_read;
+                array_list.expandToCapacity();
+                const dest_slice = array_list.span()[start_index..];
+                const bytes_read = try self.readAll(dest_slice);
+                start_index += bytes_read;
+
+                if (start_index - original_len > max_append_size) {
+                    array_list.shrink(original_len + max_append_size);
+                    return error.StreamTooLong;
+                }
 
                 if (bytes_read != dest_slice.len) {
-                    buffer.shrink(actual_buf_len);
+                    array_list.shrink(start_index);
                     return;
                 }
 
-                const new_buf_size = math.min(max_size, actual_buf_len + mem.page_size);
-                if (new_buf_size == actual_buf_len) return error.StreamTooLong;
-                try buffer.resize(new_buf_size);
+                // This will trigger ArrayList to expand superlinearly at whatever its growth rate is.
+                try array_list.ensureCapacity(start_index + 1);
             }
         }
 
@@ -89,20 +105,23 @@ pub fn InStream(comptime ReadError: type) type {
         /// Caller owns returned memory.
         /// If this function returns an error, the contents from the stream read so far are lost.
         pub fn readAllAlloc(self: *Self, allocator: *mem.Allocator, max_size: usize) ![]u8 {
-            var buf = Buffer.initNull(allocator);
-            defer buf.deinit();
-
-            try self.readAllBuffer(&buf, max_size);
-            return buf.toOwnedSlice();
+            var array_list = std.ArrayList(u8).init(allocator);
+            defer array_list.deinit();
+            try self.readAllArrayList(&array_list, max_size);
+            return array_list.toOwnedSlice();
         }
 
-        /// Replaces `buffer` contents by reading from the stream until `delimiter` is found.
+        /// Replaces the `std.ArrayList` contents by reading from the stream until `delimiter` is found.
         /// Does not include the delimiter in the result.
-        /// If `buffer.len()` would exceed `max_size`, `error.StreamTooLong` is returned and the contents
-        /// read from the stream so far are lost.
-        pub fn readUntilDelimiterBuffer(self: *Self, buffer: *Buffer, delimiter: u8, max_size: usize) !void {
-            try buffer.resize(0);
-
+        /// If the `std.ArrayList` length would exceed `max_size`, `error.StreamTooLong` is returned and the
+        /// `std.ArrayList` is populated with `max_size` bytes from the stream.
+        pub fn readUntilDelimiterArrayList(
+            self: *Self,
+            array_list: *std.ArrayList(u8),
+            delimiter: u8,
+            max_size: usize,
+        ) !void {
+            array_list.shrink(0);
             while (true) {
                 var byte: u8 = try self.readByte();
 
@@ -110,11 +129,11 @@ pub fn InStream(comptime ReadError: type) type {
                     return;
                 }
 
-                if (buffer.len() == max_size) {
+                if (array_list.len == max_size) {
                     return error.StreamTooLong;
                 }
 
-                try buffer.appendByte(byte);
+                try array_list.append(byte);
             }
         }
 
@@ -122,12 +141,16 @@ pub fn InStream(comptime ReadError: type) type {
         /// memory would be greater than `max_size`, returns `error.StreamTooLong`.
         /// Caller owns returned memory.
         /// If this function returns an error, the contents from the stream read so far are lost.
-        pub fn readUntilDelimiterAlloc(self: *Self, allocator: *mem.Allocator, delimiter: u8, max_size: usize) ![]u8 {
-            var buf = Buffer.initNull(allocator);
-            defer buf.deinit();
-
-            try self.readUntilDelimiterBuffer(&buf, delimiter, max_size);
-            return buf.toOwnedSlice();
+        pub fn readUntilDelimiterAlloc(
+            self: *Self,
+            allocator: *mem.Allocator,
+            delimiter: u8,
+            max_size: usize,
+        ) ![]u8 {
+            var array_list = std.ArrayList(u8).init(allocator);
+            defer array_list.deinit();
+            try self.readUntilDelimiterArrayList(&array_list, delimiter, max_size);
+            return array_list.toOwnedSlice();
         }
 
         /// Reads from the stream until specified byte is found. If the buffer is not
diff --git a/lib/std/process.zig b/lib/std/process.zig
index 01b9947518..084aec4c49 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -3,7 +3,6 @@ const builtin = std.builtin;
 const os = std.os;
 const fs = std.fs;
 const BufMap = std.BufMap;
-const Buffer = std.Buffer;
 const mem = std.mem;
 const math = std.math;
 const Allocator = mem.Allocator;
@@ -266,7 +265,7 @@ pub const ArgIteratorWindows = struct {
     }
 
     fn internalNext(self: *ArgIteratorWindows, allocator: *Allocator) NextError![]u8 {
-        var buf = try Buffer.initSize(allocator, 0);
+        var buf = std.ArrayList(u8).init(allocator);
         defer buf.deinit();
 
         var backslash_count: usize = 0;
@@ -282,10 +281,10 @@ pub const ArgIteratorWindows = struct {
                     if (quote_is_real) {
                         self.seen_quote_count += 1;
                         if (self.seen_quote_count == self.quote_count and self.seen_quote_count % 2 == 1) {
-                            try buf.appendByte('"');
+                            try buf.append('"');
                         }
                     } else {
-                        try buf.appendByte('"');
+                        try buf.append('"');
                     }
                 },
                 '\\' => {
@@ -295,7 +294,7 @@ pub const ArgIteratorWindows = struct {
                     try self.emitBackslashes(&buf, backslash_count);
                     backslash_count = 0;
                     if (self.seen_quote_count % 2 == 1 and self.seen_quote_count != self.quote_count) {
-                        try buf.appendByte(byte);
+                        try buf.append(byte);
                     } else {
                         return buf.toOwnedSlice();
                     }
@@ -303,16 +302,16 @@ pub const ArgIteratorWindows = struct {
                 else => {
                     try self.emitBackslashes(&buf, backslash_count);
                     backslash_count = 0;
-                    try buf.appendByte(byte);
+                    try buf.append(byte);
                 },
             }
         }
     }
 
-    fn emitBackslashes(self: *ArgIteratorWindows, buf: *Buffer, emit_count: usize) !void {
+    fn emitBackslashes(self: *ArgIteratorWindows, buf: *std.ArrayList(u8), emit_count: usize) !void {
         var i: usize = 0;
         while (i < emit_count) : (i += 1) {
-            try buf.appendByte('\\');
+            try buf.append('\\');
         }
     }
 
@@ -410,7 +409,7 @@ pub fn argsAlloc(allocator: *mem.Allocator) ![][]u8 {
 
     // TODO refactor to only make 1 allocation.
     var it = args();
-    var contents = try Buffer.initSize(allocator, 0);
+    var contents = std.ArrayList(u8).init(allocator);
     defer contents.deinit();
 
     var slice_list = std.ArrayList(usize).init(allocator);
@@ -419,7 +418,7 @@ pub fn argsAlloc(allocator: *mem.Allocator) ![][]u8 {
     while (it.next(allocator)) |arg_or_err| {
         const arg = try arg_or_err;
         defer allocator.free(arg);
-        try contents.append(arg);
+        try contents.appendSlice(arg);
         try slice_list.append(arg.len);
     }