fix PreferenceChangeEvent<T> type

Despite precisely knowing for a given `preferenceName` what its
associated type for `newValue` and `oldValue` should be, the current
typing wasn't allowing TypeScript to properly infer the type.

With this commit, we can do things like:

```ts
declare const event: PreferenceChangeEvent<{ a: string, b: number }>
if (event.preferenceName === 'a') {
    event.newValue // type is `string`
}
```

It is worth explaining the new type for the `PreferenceChangeEvent`:

```ts
// Given T:
type T = { a: string, b: number }

// We construct a new type such as:
type U = {
    a: {
        preferenceName: 'a'
	newValue: string
	oldValue?: string
    }
    b: {
       preferenceName: 'b'
       newValue: number
       oldValue?: number
    }
}

// Then we get the union of all values of U by selecting by `keyof T`:
type V = U[keyof T]

// Implementation:
type PreferenceChangeEvent<T> = {
    // Create a mapping where each key is a key from T,
    // -? normalizes optional typings to avoid getting
    // `undefined` as part of the final union:
    [K in keyof T]-?: {
        // In this object, K will take the value of each
	// independent key from T:
        preferenceName: K
	newValue: T[K]
	oldValue?: T[K]
    // Finally we create the union by doing so:
    }[keyof T]
}
```

The type is more complex, but it now represents how it is meant to be
used rather than getting tsserver lost like before.

This commit also fixes places where the typing was broken and makes use
of the new information.

Signed-off-by: Paul Maréchal <[email protected]>

examples/api-samples/src/browser/file-watching/sample-file-watching-contribution.ts

@@ -69,7 +69,7 @@ class SampleFileWatchingContribution implements FrontendApplicationContribution
         this.verbose = this.fileWatchingPreferences['sample.file-watching.verbose'];
         this.fileWatchingPreferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'sample.file-watching.verbose') {
-                this.verbose = e.newValue!;
+                this.verbose = e.newValue;
             }
         });
     }

packages/core/src/browser/preferences/preference-proxy.ts

@@ -21,12 +21,19 @@ import { PreferenceService } from './preference-service';
 import { PreferenceSchema, OverridePreferenceName } from './preference-contribution';
 import { PreferenceScope } from './preference-scope';
 
-export interface PreferenceChangeEvent<T> {
-    readonly preferenceName: keyof T;
-    readonly newValue?: T[keyof T];
-    readonly oldValue?: T[keyof T];
+export type PreferenceChangeEvent<T> = {
     affects(resourceUri?: string, overrideIdentifier?: string): boolean;
-}
+} & {
+    [K in keyof T]-?: {
+        readonly preferenceName: K;
+        readonly newValue: T[K];
+        /**
+         * Undefined if the preference is set for the first time.
+         */
+        // TODO: Use the default value instead of undefined?
+        readonly oldValue?: T[K];
+    }
+}[keyof T];
 
 export interface PreferenceEventEmitter<T> {
     readonly onPreferenceChanged: Event<PreferenceChangeEvent<T>>;

packages/git/src/browser/diff/git-diff-widget.tsx

@@ -25,7 +25,7 @@ import { GitDiffHeaderWidget } from './git-diff-header-widget';
 import { ScmService } from '@theia/scm/lib/browser/scm-service';
 import { GitRepositoryProvider } from '../git-repository-provider';
 import { ScmTreeWidget } from '@theia/scm/lib/browser/scm-tree-widget';
-import { ScmPreferences, ScmConfiguration } from '@theia/scm/lib/browser/scm-preferences';
+import { ScmPreferences } from '@theia/scm/lib/browser/scm-preferences';
 
 /* eslint-disable @typescript-eslint/no-explicit-any */
 
@@ -76,9 +76,9 @@ export class GitDiffWidget extends BaseWidget implements StatefulWidget {
         this.containerLayout.addWidget(this.resourceWidget);
 
         this.updateViewMode(this.scmPreferences.get('scm.defaultViewMode'));
-        this.toDispose.push(this.scmPreferences.onPreferenceChanged((e: PreferenceChangeEvent<ScmConfiguration>) => {
+        this.toDispose.push(this.scmPreferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'scm.defaultViewMode') {
-                this.updateViewMode(e.newValue!);
+                this.updateViewMode(e.newValue);
             }
         }));
     }

packages/git/src/browser/history/git-commit-detail-widget.tsx

@@ -76,9 +76,9 @@ export class GitCommitDetailWidget extends BaseWidget implements StatefulWidget
         this.containerLayout.addWidget(this.resourceWidget);
 
         this.updateViewMode(this.scmPreferences.get('scm.defaultViewMode'));
-        this.toDispose.push(this.scmPreferences.onPreferenceChanged((e: PreferenceChangeEvent<ScmConfiguration>) => {
+        this.toDispose.push(this.scmPreferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'scm.defaultViewMode') {
-                this.updateViewMode(e.newValue!);
+                this.updateViewMode(e.newValue);
             }
         }));
 

packages/markers/src/browser/problem/problem-decorator.ts

@@ -46,10 +46,9 @@ export class ProblemDecorator implements TreeDecorator {
 
     @postConstruct()
     protected init(): void {
-        this.problemPreferences.onPreferenceChanged((event: PreferenceChangeEvent<ProblemConfiguration>) => {
-            const { preferenceName } = event;
-            if (preferenceName === 'problems.decorations.enabled') {
-                this.fireDidChangeDecorations((tree: Tree) => this.collectDecorators(tree));
+        this.problemPreferences.onPreferenceChanged(event => {
+            if (event.preferenceName === 'problems.decorations.enabled') {
+                this.fireDidChangeDecorations(tree => this.collectDecorators(tree));
             }
         });
     }

packages/monaco/src/browser/textmate/monaco-textmate-service.ts

@@ -103,7 +103,7 @@ export class MonacoTextmateService implements FrontendApplicationContribution {
         this.tokenizerOption.lineLimit = this.preferences['editor.maxTokenizationLineLength'];
         this.preferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'editor.maxTokenizationLineLength') {
-                this.tokenizerOption.lineLimit = this.preferences['editor.maxTokenizationLineLength'];
+                this.tokenizerOption.lineLimit = e.newValue;
             }
         });
 

packages/output/src/common/output-channel.ts

@@ -221,9 +221,9 @@ export class OutputChannel implements Disposable {
         this._maxLineNumber = this.preferences['output.maxChannelHistory'];
         this.toDispose.push(resource);
         this.toDispose.push(Disposable.create(() => this.decorationIds.clear()));
-        this.toDispose.push(this.preferences.onPreferenceChanged(({ preferenceName, newValue }) => {
-            if (preferenceName === 'output.maxChannelHistory') {
-                const maxLineNumber = newValue ? newValue : OutputConfigSchema.properties['output.maxChannelHistory'].default;
+        this.toDispose.push(this.preferences.onPreferenceChanged(event => {
+            if (event.preferenceName === 'output.maxChannelHistory') {
+                const maxLineNumber = event.newValue;
                 if (this.maxLineNumber !== maxLineNumber) {
                     this.maxLineNumber = maxLineNumber;
                 }

packages/preview/src/browser/preview-widget.ts

@@ -83,7 +83,7 @@ export class PreviewWidget extends BaseWidget implements Navigatable {
         this.scrollBeyondLastLine = !!this.editorPreferences['editor.scrollBeyondLastLine'];
         this.toDispose.push(this.editorPreferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'editor.scrollBeyondLastLine') {
-                this.scrollBeyondLastLine = !!e.newValue;
+                this.scrollBeyondLastLine = e.newValue;
                 this.forceUpdate();
             }
         }));

packages/scm/src/browser/scm-widget.tsx

@@ -78,9 +78,9 @@ export class ScmWidget extends BaseWidget implements StatefulWidget {
         this.refresh();
         this.toDispose.push(this.scmService.onDidChangeSelectedRepository(() => this.refresh()));
         this.updateViewMode(this.scmPreferences.get('scm.defaultViewMode'));
-        this.toDispose.push(this.scmPreferences.onPreferenceChanged((e: PreferenceChangeEvent<ScmConfiguration>) => {
+        this.toDispose.push(this.scmPreferences.onPreferenceChanged(e => {
             if (e.preferenceName === 'scm.defaultViewMode') {
-                this.updateViewMode(e.newValue!);
+                this.updateViewMode(e.newValue);
             }
         }));
 

packages/terminal/src/browser/terminal-preferences.ts

@@ -151,6 +151,7 @@ export const TerminalConfigSchema: PreferenceSchema = {
 export interface TerminalConfiguration {
     'terminal.enableCopy': boolean
     'terminal.enablePaste': boolean
+    // xterm compatible, see https://xtermjs.org/docs/api/terminal/interfaces/iterminaloptions/
     'terminal.integrated.fontFamily': string
     'terminal.integrated.fontSize': number
     'terminal.integrated.fontWeight': FontWeight
@@ -165,9 +166,9 @@ export interface TerminalConfiguration {
     'terminal.integrated.cursorBlinking': boolean,
     'terminal.integrated.cursorStyle': CursorStyleVSCode,
     'terminal.integrated.cursorWidth': number,
-    'terminal.integrated.shell.windows': string | undefined,
-    'terminal.integrated.shell.osx': string | undefined,
-    'terminal.integrated.shell.linux': string | undefined,
+    'terminal.integrated.shell.windows': string | null | undefined,
+    'terminal.integrated.shell.osx': string | null | undefined,
+    'terminal.integrated.shell.linux': string | null | undefined,
     'terminal.integrated.shellArgs.windows': string[],
     'terminal.integrated.shellArgs.osx': string[],
     'terminal.integrated.shellArgs.linux': string[],

packages/terminal/src/browser/terminal-widget-impl.ts

@@ -148,18 +148,16 @@ export class TerminalWidgetImpl extends TerminalWidget implements StatefulWidget
             const lastSeparator = change.preferenceName.lastIndexOf('.');
             if (lastSeparator > 0) {
                 let preferenceName = change.preferenceName.substr(lastSeparator + 1);
-                let preferenceValue = this.preferences[change.preferenceName];
+                let preferenceValue = change.newValue;
 
                 if (preferenceName === 'rendererType') {
-                    const newRendererType: string = this.preferences[change.preferenceName] as string;
+                    const newRendererType = preferenceValue as string;
                     if (newRendererType !== this.getTerminalRendererType(newRendererType)) {
-                        // given terminal renderer type is not supported or invalid
+                        // Given terminal renderer type is not supported or invalid
                         preferenceValue = DEFAULT_TERMINAL_RENDERER_TYPE;
                     }
-                }
-
-                // Convert the terminal preference into a valid `xterm` option.
-                if (preferenceName === 'cursorBlinking') {
+                } else if (preferenceName === 'cursorBlinking') {
+                    // Convert the terminal preference into a valid `xterm` option
                     preferenceName = 'cursorBlink';
                 } else if (preferenceName === 'cursorStyle') {
                     preferenceValue = this.getCursorStyle();

packages/workspace/src/browser/workspace-service.ts

@@ -95,8 +95,8 @@ export class WorkspaceService implements FrontendApplicationContribution {
                 this.updateWorkspace();
             }
         });
-        this.fsPreferences.onPreferenceChanged(e => {
-            if (e.preferenceName === 'files.watcherExclude') {
+        this.fsPreferences.onPreferenceChanged(event => {
+            if (event.preferenceName === 'files.watcherExclude') {
                 this.refreshRootWatchers();
             }
         });