text: Bundle 'Source Code Pro' font in the app; use it for code blocks/spans in messages

assets/Source_Code_Pro/LICENSE.md

@@ -0,0 +1,93 @@
+© 2023 Adobe (http://www.adobe.com/), with Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of Adobe in the United States and/or other countries.
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+
+This license is copied below, and is also available with a FAQ at: http://scripts.sil.org/OFL
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded,
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.

lib/licenses.dart

@@ -0,0 +1,16 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+/// Our [LicenseEntryCollector] for licenses that aren't included by default.
+///
+/// Licenses that ship with our Dart-package dependencies are included
+/// automatically. This collects other licenses, such as for fonts we include in
+/// our asset bundle.
+// If the license text is meant to be read from a file in the asset bundle,
+// remember to include the file in the asset bundle by listing its path
+// under `assets` in pubspec.yaml.
+Stream<LicenseEntry> additionalLicenses() async* {
+  yield LicenseEntryWithLineBreaks(
+    ['Source Code Pro'],
+    await rootBundle.loadString('assets/Source_Code_Pro/LICENSE.md'));
+}

lib/main.dart

@@ -1,5 +1,7 @@
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
+import 'licenses.dart';
 import 'log.dart';
 import 'widgets/app.dart';
 
@@ -8,5 +10,6 @@ void main() {
     debugLogEnabled = true;
     return true;
   }());
+  LicenseRegistry.addLicense(additionalLicenses);
   runApp(const ZulipApp());
 }

lib/widgets/content.dart

@@ -7,6 +7,7 @@ import '../model/content.dart';
 import '../model/store.dart';
 import 'store.dart';
 import 'lightbox.dart';
+import 'text.dart';
 
 /// The font size for message content in a plain unstyled paragraph.
 const double kBaseFontSize = 14;
@@ -251,7 +252,7 @@ class CodeBlock extends StatelessWidget {
           color: const HSLColor.fromAHSL(0.15, 0, 0, 0).toColor())),
       child: SingleChildScrollViewWithScrollbar(
         scrollDirection: Axis.horizontal,
-        child: Text(text, style: _kCodeStyle)));
+        child: Text(text, style: _kCodeBlockStyle)));
   }
 }
 
@@ -351,13 +352,7 @@ InlineSpan inlineCode(InlineCodeNode node) {
   // TODO `code`: find equivalent of web's `unicode-bidi: embed; direction: ltr`
 
   // Use a light gray background, instead of a border.
-  return TextSpan(
-    style: const TextStyle(
-      backgroundColor: Color(0xffeeeeee),
-      fontSize: 0.825 * kBaseFontSize,
-      fontFamily: "Source Code Pro", // TODO supply font
-      fontFamilyFallback: ["monospace"],
-    ),
+  return TextSpan(style: _kInlineCodeStyle,
     children: _buildInlineList(node.nodes));
 
   // Another fun solution -- we can in fact have a border!  Like so:
@@ -377,12 +372,25 @@ InlineSpan inlineCode(InlineCodeNode node) {
   // ]);
 }
 
-const _kCodeStyle = TextStyle(
-  backgroundColor: Color.fromRGBO(255, 255, 255, 1),
-  fontSize: 0.825 * kBaseFontSize,
-  fontFamily: "Source Code Pro", // TODO supply font
-  fontFamilyFallback: ["monospace"],
-);
+final _kInlineCodeStyle = kMonospaceTextStyle
+  .merge(const TextStyle(
+    backgroundColor: Color(0xffeeeeee),
+    fontSize: 0.825 * kBaseFontSize))
+  .merge(
+    // TODO(a11y) pass a BuildContext, to handle platform request for bold text.
+    //   To get one, the result of this whole computation (to the TextStyle
+    //   we get at the end) could live on one [InheritedWidget], at the
+    //   MessageList or higher, so the computation doesn't get repeated
+    //   frequently. Then consumers can just look it up on the InheritedWidget.
+    weightVariableTextStyle(null));
+
+final _kCodeBlockStyle = kMonospaceTextStyle
+  .merge(const TextStyle(
+    backgroundColor: Color.fromRGBO(255, 255, 255, 1),
+    fontSize: 0.825 * kBaseFontSize))
+  .merge(
+    // TODO(a11y) pass a BuildContext; see comment in _kInlineCodeStyle above.
+    weightVariableTextStyle(null));
 
 // const _kInlineCodeLeftBracket = '⸤';
 // const _kInlineCodeRightBracket = '⸣';
@@ -639,4 +647,6 @@ InlineSpan _errorUnimplemented(UnimplementedNode node) {
 
 const errorStyle = TextStyle(fontWeight: FontWeight.bold, color: Colors.red);
 
-const errorCodeStyle = TextStyle(color: Colors.red, fontFamily: 'monospace');
+final errorCodeStyle = kMonospaceTextStyle
+  .merge(const TextStyle(color: Colors.red))
+  .merge(weightVariableTextStyle(null)); // TODO(a11y) pass a BuildContext

lib/widgets/text.dart

@@ -0,0 +1,102 @@
+import 'dart:io';
+import 'dart:ui';
+import 'package:flutter/widgets.dart';
+
+/// A mergeable [TextStyle] with 'Source Code Pro' and platform-aware fallbacks.
+///
+/// Callers should also call [weightVariableTextStyle] and merge that in too,
+/// because for this font, we use "variable font" assets with a "wght" axis.
+///
+/// Example:
+///
+/// ```dart
+/// kMonospaceTextStyle
+///   .merge(const TextStyle(color: Colors.red))
+///   .merge(weightVariableTextStyle(context))
+/// ```
+final TextStyle kMonospaceTextStyle = TextStyle(
+  fontFamily: 'Source Code Pro',
+
+  // Oddly, iOS doesn't handle 'monospace':
+  //   https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/flutter.3A.20monospace.20font.20fallback/near/1570622
+  fontFamilyFallback: Platform.isIOS ? ['Menlo', 'Courier'] : ['monospace'],
+
+  inherit: true,
+);
+
+/// A mergeable [TextStyle] to use when the preferred font has a "wght" axis.
+///
+/// Some variable fonts can be controlled on a "wght" axis.
+/// Use this to set a value on that axis. It uses [TextStyle.fontVariations],
+/// along with a [TextStyle.fontWeight] that approximates the given "wght"
+/// for the sake of glyphs that need to be rendered by a fallback font
+/// (which might not offer a "wght" axis).
+///
+/// Use this even to specify normal-weight text, by omitting `wght`; then,
+/// [FontWeight.normal.value] will be used. No other layer applies a default,
+/// so if you don't use this, you may e.g. get the font's lightest weight.
+///
+/// Pass [context] to respect a platform request to draw bold text for
+/// accessibility (see [MediaQueryData.boldText]). This handles that request by
+/// using [wghtIfPlatformRequestsBold] or if that's null, [FontWeight.bold.value].
+///
+/// Example:
+///
+/// ```dart
+/// someTextStyle.merge(weightVariableTextStyle(context, wght: 250)
+/// ```
+///
+/// See also [FontVariation] for more background on variable fonts.
+// TODO(a11y) make `context` required when callers can adapt?
+TextStyle weightVariableTextStyle(BuildContext? context, {
+  double? wght,
+  double? wghtIfPlatformRequestsBold,
+}) {
+  assert((wght != null) == (wghtIfPlatformRequestsBold != null));
+  double value = wght ?? FontWeight.normal.value.toDouble();
+  if (context != null && MediaQuery.of(context).boldText) {
+    // The framework has a condition on [MediaQueryData.boldText]
+    // in the [Text] widget, but that only affects `fontWeight`.
+    // [Text] doesn't know where to land on the chosen font's "wght" axis if any,
+    // and indeed it doesn't seem updated to be aware of variable fonts at all.
+    value = wghtIfPlatformRequestsBold ?? FontWeight.bold.value.toDouble();
+  }
+  assert(value >= 1 && value <= 1000); // https://fonts.google.com/variablefonts#axis-definitions
+
+  return TextStyle(
+    fontVariations: [FontVariation('wght', value)],
+
+    // This use of `fontWeight` shouldn't affect glyphs in the preferred,
+    // "wght"-axis font. If it does, see for debugging:
+    //   https://github.com./zulip/zulip-flutter/issues/65#issuecomment-1550666764
+    fontWeight: clampVariableFontWeight(value),
+
+    inherit: true);
+}
+
+/// Find the nearest [FontWeight] constant for a variable-font "wght"-axis value.
+///
+/// Use this for a reasonable [TextStyle.fontWeight] for glyphs that need to be
+/// rendered by a fallback font that doesn't have a "wght" axis.
+///
+/// See also [FontVariation] for background on variable fonts.
+FontWeight clampVariableFontWeight(double wght) {
+  if (wght < 450) {
+    if (wght < 250) {
+      if (wght < 150)      return FontWeight.w100; // ignore_for_file: curly_braces_in_flow_control_structures
+      else                 return FontWeight.w200;
+    } else {
+      if (wght < 350)      return FontWeight.w300;
+      else                 return FontWeight.w400;
+    }
+  } else {
+    if (wght < 650) {
+      if (wght < 550)      return FontWeight.w500;
+      else                 return FontWeight.w600;
+    } else {
+      if (wght < 750)      return FontWeight.w700;
+      else if (wght < 850) return FontWeight.w800;
+      else                 return FontWeight.w900;
+    }
+  }
+}

pubspec.yaml

@@ -85,33 +85,13 @@ flutter:
   # the material Icons class.
   uses-material-design: true
 
-  # To add assets to your application, add an assets section, like this:
-  # assets:
-  #   - images/a_dot_burr.jpeg
-  #   - images/a_dot_ham.jpeg
+  assets:
+    - assets/Source_Code_Pro/LICENSE.md
 
-  # An image asset can refer to one or more resolution-specific "variants", see
-  # https://flutter.dev/assets-and-images/#resolution-aware
-
-  # For details regarding adding assets from package dependencies, see
-  # https://flutter.dev/assets-and-images/#from-packages
-
-  # To add custom fonts to your application, add a fonts section here,
-  # in this "flutter" section. Each entry in this list should have a
-  # "family" key with the font family name, and a "fonts" key with a
-  # list giving the asset and other descriptors for the font. For
-  # example:
-  # fonts:
-  #   - family: Schyler
-  #     fonts:
-  #       - asset: fonts/Schyler-Regular.ttf
-  #       - asset: fonts/Schyler-Italic.ttf
-  #         style: italic
-  #   - family: Trajan Pro
-  #     fonts:
-  #       - asset: fonts/TrajanPro.ttf
-  #       - asset: fonts/TrajanPro_Bold.ttf
-  #         weight: 700
-  #
-  # For details regarding fonts from package dependencies,
-  # see https://flutter.dev/custom-fonts/#from-packages
+  # If adding a font, remember to account for its license in lib/licenses.dart.
+  fonts:
+    - family: Source Code Pro
+      fonts:
+        - asset: assets/Source_Code_Pro/SourceCodeVF-Upright.otf
+        - asset: assets/Source_Code_Pro/SourceCodeVF-Italic.otf
+          style: italic

test/flutter_checks.dart

@@ -0,0 +1,13 @@
+/// `package:checks`-related extensions for the Flutter framework.
+import 'dart:ui';
+
+import 'package:checks/checks.dart';
+import 'package:flutter/painting.dart';
+
+extension TextStyleChecks on Subject<TextStyle> {
+  Subject<bool> get inherit => has((t) => t.inherit, 'inherit');
+  Subject<List<FontVariation>?> get fontVariations => has((t) => t.fontVariations, 'fontVariations');
+  Subject<FontWeight?> get fontWeight => has((t) => t.fontWeight, 'fontWeight');
+
+  // TODO others
+}