use build.zig.zon instead of build.zig.ini for the manifest file

 * improve error message when build manifest file is missing
 * update std.zig.Ast to support ZON
 * Compilation.AllErrors.Message: make the notes field a const slice
 * move build manifest parsing logic into src/Manifest.zig and add more
   checks, and make the checks integrate into the standard error
   reporting code so that reported errors look sexy

closes #14290

lib/std/Build.zig

@@ -1496,8 +1496,8 @@ pub fn dependency(b: *Build, name: []const u8, args: anytype) *Dependency {
         }
     }
 
-    const full_path = b.pathFromRoot("build.zig.ini");
-    std.debug.print("no dependency named '{s}' in '{s}'\n", .{ name, full_path });
+    const full_path = b.pathFromRoot("build.zig.zon");
+    std.debug.print("no dependency named '{s}' in '{s}'. All packages used in build.zig must be declared in this file.\n", .{ name, full_path });
     std.process.exit(1);
 }
 

lib/std/array_hash_map.zig

@@ -1145,7 +1145,8 @@ pub fn ArrayHashMapUnmanaged(
         }
 
         /// Create a copy of the hash map which can be modified separately.
-        /// The copy uses the same context and allocator as this instance.
+        /// The copy uses the same context as this instance, but is allocated
+        /// with the provided allocator.
         pub fn clone(self: Self, allocator: Allocator) !Self {
             if (@sizeOf(ByIndexContext) != 0)
                 @compileError("Cannot infer context " ++ @typeName(Context) ++ ", call cloneContext instead.");

lib/std/zig/Ast.zig

@@ -1,4 +1,8 @@
 //! Abstract Syntax Tree for Zig source code.
+//! For Zig syntax, the root node is at nodes[0] and contains the list of
+//! sub-nodes.
+//! For Zon syntax, the root node is at nodes[0] and contains lhs as the node
+//! index of the main expression.
 
 /// Reference to externally-owned data.
 source: [:0]const u8,

lib/std/zig/Parse.zig

@@ -181,17 +181,26 @@ pub fn parseRoot(p: *Parse) !void {
 /// TODO: set a flag in Parse struct, and honor that flag
 /// by emitting compilation errors when non-zon nodes are encountered.
 pub fn parseZon(p: *Parse) !void {
-    const node_index = p.parseExpr() catch |err| switch (err) {
+    // We must use index 0 so that 0 can be used as null elsewhere.
+    p.nodes.appendAssumeCapacity(.{
+        .tag = .root,
+        .main_token = 0,
+        .data = undefined,
+    });
+    const node_index = p.expectExpr() catch |err| switch (err) {
         error.ParseError => {
             assert(p.errors.items.len > 0);
             return;
         },
         else => |e| return e,
     };
-    assert(node_index == 0);
     if (p.token_tags[p.tok_i] != .eof) {
         try p.warnExpected(.eof);
     }
+    p.nodes.items(.data)[0] = .{
+        .lhs = node_index,
+        .rhs = undefined,
+    };
 }
 
 /// ContainerMembers <- ContainerDeclarations (ContainerField COMMA)* (ContainerField / ContainerDeclarations)

src/Compilation.zig

@@ -385,7 +385,7 @@ pub const AllErrors = struct {
             count: u32 = 1,
             /// Does not include the trailing newline.
             source_line: ?[]const u8,
-            notes: []Message = &.{},
+            notes: []const Message = &.{},
             reference_trace: []Message = &.{},
 
             /// Splits the error message up into lines to properly indent them