(themes) Implementation idea on new design tokens handling

Until now themes could only describe each component variable. This made
creating a theme difficult: we had to override all component variables
(hundreds of them) if we wanted to change one color shade used globally.

Here is an idea of a cssVars.designTokens prop that is a combination of
current `colors`, `vars` and `theme` props:

- all design tokens are overridable by a theme
- colors are now named in a more abstract way so that it makes sense for
a theme changing the primary color

Everything is explained in details in the cssVars.designTokens comments

app/client/app.css

@@ -1,5 +1,5 @@
 /* global variables */
-@layer grist-base, grist-theme, grist-custom;
+@layer grist-base, grist-tokens, grist-theme, grist-custom;
 :root {
   --color-logo-row:  #F9AE41;
   --color-logo-col:  #2CB0AF;

app/client/ui2018/cssVars.ts

@@ -16,7 +16,7 @@ import values = require('lodash/values');
 const VAR_PREFIX = 'grist';
 
 class CustomProp {
-  constructor(public name: string, public value?: string, public fallback?: string | CustomProp) {
+  constructor(public name: string, public value?: string | CustomProp, public fallback?: string | CustomProp) {
 
   }
 
@@ -78,6 +78,89 @@ export const colors = {
 
 };
 
+/**
+ * Example of new "design tokens" that are a mix of current `colors`, `vars` and `theme` props.
+ *
+ * The css variables defined here take precedence over the ones in `colors` and `vars`, but are
+ * overriden by variables re-declared in a theme or a custom css file.
+ *
+ * The idea is we would not need `colors` and `vars` anymore.
+ *
+ * 1) List the `colors` above but rename them to have more abstracted names, ie "lightGreen" becomes "primaryLight".
+ * Grays are an exception here as I assume they will always be targetted as such, but we could name them differently
+ * if we want to stick to non-visual names here, like "shadeXX", "neutralXX". Or "secondaryXX", renaming the current
+ * "secondary" color to "tertiary" or "accent"? I just followed original naming for now.
+ *
+ * 2) Whenever possible, design tokens target other design tokens instead of copying color codes, ie "primaryBg"
+ * directly targets "primaryLight" instead of being "#16B378". Here I use getters to define tokens that target other
+ * tokens to prevent having to define multiple temporary vars.
+ *
+ * 3) Follow the `vars` object idea and add more semantic/global tokens to the list.
+ * What I have in mind is to move most of `vars` props here, and some of the pretty-much global things listed in `theme`
+ * (like text colors or panel global things). The endgoal would be to list all colors and tokens globally used in
+ * Grist here. I guess it might not make sense to list here a few really specific components (for example, code view).
+ *
+ * 4) Either have component-specific variables listed in `theme` below consume these designTokens, *or* remove
+ * them and make it so that components directly consume the designTokens in their own code.
+ *
+ * Colors listed here default to Grist light theme colors.
+ * Contrary to `colors` and `vars`, all tokens here are meant to be overridable by a theme,
+ * allowing a theme to only override what it wants instead of having to redefine everything.
+ */
+export const designTokens = {
+  /* first list hard-coded colors, then other colors consuming them and other non-color tokens */
+  white: new CustomProp('color-white', '#FFFFFF'),
+  greyLight: new CustomProp('color-grey-light', '#F7F7F7'),
+  greyMediumOpaque: new CustomProp('color-grey-medium-opaque', '#E8E8E8'),
+  greyMedium: new CustomProp('color-grey-medium', 'rgba(217,217,217,0.6)'),
+  greyDark: new CustomProp('color-grey-dark', '#D9D9D9'),
+  slate: new CustomProp('color-slate', '#929299'),
+  darkText: new CustomProp('color-dark-text', '#494949'),
+  dark: new CustomProp('color-dark', '#262633'),
+  black: new CustomProp('color-black', '#000000'),
+
+  primaryLighter: new CustomProp('color-primary-lighter', '#b1ffe2'),
+  primaryLight: new CustomProp('color-primary-light', '#16B378'),
+  primaryDark: new CustomProp('color-primary-dark', '#009058'),
+  primaryDarker: new CustomProp('color-primary-darker', '#007548'),
+
+  secondaryLighter: new CustomProp('color-secondary-lighter', '#87b2f9'),
+  secondaryLight: new CustomProp('color-secondary-light', '#3B82F6'),
+
+  error: new CustomProp('color-error', '#D0021B'),
+  warningLight: new CustomProp('color-warning-light', '#F9AE41'),
+  warningDark: new CustomProp('color-warning-dark', '#dd962c'),
+
+  cursorInactive: new CustomProp('color-cursor-inactive', '#A2E1C9'),
+  selection: new CustomProp('color-selection', 'rgba(22,179,120,0.15)'),
+  selectionOpaque: new CustomProp('color-selection-opaque', '#DCF4EB'),
+  selectionDarkerOpaque: new CustomProp('color-selection-darker-opaque', '#d6eee5'),
+  hover: new CustomProp('color-hover', '#bfbfbf'),
+  backdrop: new CustomProp('color-backdrop', 'rgba(38,38,51,0.9)'),
+
+  get warningBg() { return new CustomProp('color-warning-bg', this.warningDark); },
+
+  get primaryBg() { return new CustomProp('primary-bg', this.primaryLight); },
+  get primaryBgHover() { return new CustomProp('primary-bg-hover', this.primaryDark); },
+  get primaryFg() { return new CustomProp('primary-fg', this.white); },
+
+  get controlBg() { return new CustomProp('control-bg', this.white); },
+  get controlFg() { return new CustomProp('control-fg', this.primaryLight); },
+  get controlFgHover() { return new CustomProp('primary-fg-hover', this.primaryDark); },
+  get controlBorderColor() { return new CustomProp('control-border-color', this.primaryLight); },
+  controlBorderRadius: new CustomProp('border-radius', '4px'),
+
+  get cursor() { return new CustomProp('color-cursor', this.primaryLight); },
+
+  get mainBg() { return new CustomProp('main-bg', this.white); },
+  get text() { return new CustomProp('text', this.dark); },
+  get textLight() { return new CustomProp('text-light', this.slate); },
+
+  get panelBg() { return new CustomProp('panel-bg', this.greyLight); },
+  get panelFg() { return new CustomProp('panel-fg', this.dark); },
+  get panelBorder() { return new CustomProp('panel-border', this.greyMedium); },
+};
+
 export const vars = {
   /* Fonts */
   fontFamily: new CustomProp('font-family', `-apple-system,BlinkMacSystemFont,Segoe UI,Liberation Sans,
@@ -923,6 +1006,7 @@ export const theme = {
 
 const cssColors = values(colors).map(v => v.decl()).join('\n');
 const cssVars = values(vars).map(v => v.decl()).join('\n');
+const cssTokens = values(designTokens).map(v => v.decl()).join('\n');
 
 // We set box-sizing globally to match bootstrap's setting of border-box, since we are integrating
 // into an app which already has it set, and it's impossible to make things look consistently with
@@ -1065,6 +1149,11 @@ export function attachCssRootVars(productFlavor: ProductFlavor, varsOnly: boolea
     ${cssRootVars}
   }
   ${!varsOnly && cssReset}
+}
+@layer grist-tokens {
+  :root {
+    ${cssTokens}
+  }
 }`;
   document.documentElement.classList.add(cssRoot.className);
   document.body.classList.add(cssBody.className);

app/client/ui2018/theme.ts

@@ -120,18 +120,21 @@ function getThemeFromPrefs(themePrefs: ThemePrefs, userAgentPrefersDarkTheme: bo
 }
 
 function attachCssThemeVars({appearance, colors: themeColors}: Theme) {
-  // Prepare the custom properties needed for applying the theme.
-  const properties = Object.entries(themeColors)
+  const properties = Object.entries(themeColors.legacyVariables || {})
     .map(([name, value]) => `--grist-theme-${name}: ${value};`);
 
+  properties.push(...Object.entries(themeColors || {})
+    .filter(([name]) => name !== 'legacyVariables')
+    .map(([name, value]) => `--grist-${name}: ${value};`));
+
   // Include properties for styling the scrollbar.
   properties.push(...getCssThemeScrollbarProperties(appearance));
 
   // Include properties for picking an appropriate background image.
   properties.push(...getCssThemeBackgroundProperties(appearance));
 
   // Apply the properties to the theme style element.
-  // The 'grist-theme' layer takes precedence over the 'grist-base' layer where
+  // The 'grist-theme' layer takes precedence over the 'grist-base' and 'grist-tokens'layers where
   // default CSS variables are defined.
   getOrCreateStyleElement('grist-theme').textContent = `@layer grist-theme {
   :root {

app/common/ThemePrefs.ts

@@ -22,6 +22,11 @@ export interface Theme {
 }
 
 export interface ThemeColors {
+  legacyVariables?: Partial<LegacyThemeVariables>;
+  [key: string]: any; /* TODO: improve typings, we should list explicit list of designTokens */
+}
+
+interface LegacyThemeVariables {
   /* Text */
   'text': string;
   'text-light': string;