4 files changed, 393 insertions, 0 deletions

diff --git a/editors/code/src/utils/diagnostics/SuggestedFix.ts b/editors/code/src/utils/diagnostics/SuggestedFix.ts
new file mode 100644
index 000000000..b1be2a225
--- /dev/null
+++ b/editors/code/src/utils/diagnostics/SuggestedFix.ts
@@ -0,0 +1,67 @@
+import * as vscode from 'vscode';
+
+import { SuggestionApplicability } from './rust';
+
+/**
+ * Model object for text replacements suggested by the Rust compiler
+ *
+ * This is an intermediate form between the raw `rustc` JSON and a
+ * `vscode.CodeAction`. It's optimised for the use-cases of
+ * `SuggestedFixCollection`.
+ */
+export default class SuggestedFix {
+    public readonly title: string;
+    public readonly location: vscode.Location;
+    public readonly replacement: string;
+    public readonly applicability: SuggestionApplicability;
+
+    /**
+     * Diagnostics this suggested fix could resolve
+     */
+    public diagnostics: vscode.Diagnostic[];
+
+    constructor(
+        title: string,
+        location: vscode.Location,
+        replacement: string,
+        applicability: SuggestionApplicability = SuggestionApplicability.Unspecified
+    ) {
+        this.title = title;
+        this.location = location;
+        this.replacement = replacement;
+        this.applicability = applicability;
+        this.diagnostics = [];
+    }
+
+    /**
+     * Determines if this suggested fix is equivalent to another instance
+     */
+    public isEqual(other: SuggestedFix): boolean {
+        return (
+            this.title === other.title &&
+            this.location.range.isEqual(other.location.range) &&
+            this.replacement === other.replacement &&
+            this.applicability === other.applicability
+        );
+    }
+
+    /**
+     * Converts this suggested fix to a VS Code Quick Fix code action
+     */
+    public toCodeAction(): vscode.CodeAction {
+        const codeAction = new vscode.CodeAction(
+            this.title,
+            vscode.CodeActionKind.QuickFix
+        );
+
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(this.location.uri, this.location.range, this.replacement);
+        codeAction.edit = edit;
+
+        codeAction.isPreferred =
+            this.applicability === SuggestionApplicability.MachineApplicable;
+
+        codeAction.diagnostics = [...this.diagnostics];
+        return codeAction;
+    }
+}
diff --git a/editors/code/src/utils/diagnostics/SuggestedFixCollection.ts b/editors/code/src/utils/diagnostics/SuggestedFixCollection.ts
new file mode 100644
index 000000000..132ce12f8
--- /dev/null
+++ b/editors/code/src/utils/diagnostics/SuggestedFixCollection.ts
@@ -0,0 +1,77 @@
+import * as vscode from 'vscode';
+import SuggestedFix from './SuggestedFix';
+
+/**
+ * Collection of suggested fixes across multiple documents
+ *
+ * This stores `SuggestedFix` model objects and returns them via the
+ * `vscode.CodeActionProvider` interface.
+ */
+export default class SuggestedFixCollection
+    implements vscode.CodeActionProvider {
+    public static PROVIDED_CODE_ACTION_KINDS = [vscode.CodeActionKind.QuickFix];
+
+    /**
+     * Map of document URI strings to suggested fixes
+     */
+    private suggestedFixes: Map<string, SuggestedFix[]>;
+
+    constructor() {
+        this.suggestedFixes = new Map();
+    }
+
+    /**
+     * Clears all suggested fixes across all documents
+     */
+    public clear(): void {
+        this.suggestedFixes = new Map();
+    }
+
+    /**
+     * Adds a suggested fix for the given diagnostic
+     *
+     * Some suggested fixes will appear in multiple diagnostics. For example,
+     * forgetting a `mut` on a variable will suggest changing the delaration on
+     * every mutable usage site. If the suggested fix has already been added
+     * this method will instead associate the existing fix with the new
+     * diagnostic.
+     */
+    public addSuggestedFixForDiagnostic(
+        suggestedFix: SuggestedFix,
+        diagnostic: vscode.Diagnostic
+    ): void {
+        const fileUriString = suggestedFix.location.uri.toString();
+        const fileSuggestions = this.suggestedFixes.get(fileUriString) || [];
+
+        const existingSuggestion = fileSuggestions.find(s =>
+            s.isEqual(suggestedFix)
+        );
+
+        if (existingSuggestion) {
+            // The existing suggestion also applies to this new diagnostic
+            existingSuggestion.diagnostics.push(diagnostic);
+        } else {
+            // We haven't seen this suggestion before
+            suggestedFix.diagnostics.push(diagnostic);
+            fileSuggestions.push(suggestedFix);
+        }
+
+        this.suggestedFixes.set(fileUriString, fileSuggestions);
+    }
+
+    /**
+     * Filters suggested fixes by their document and range and converts them to
+     * code actions
+     */
+    public provideCodeActions(
+        document: vscode.TextDocument,
+        range: vscode.Range
+    ): vscode.CodeAction[] {
+        const documentUriString = document.uri.toString();
+
+        const suggestedFixes = this.suggestedFixes.get(documentUriString);
+        return (suggestedFixes || [])
+            .filter(({ location }) => location.range.intersection(range))
+            .map(suggestedEdit => suggestedEdit.toCodeAction());
+    }
+}
diff --git a/editors/code/src/utils/diagnostics/rust.ts b/editors/code/src/utils/diagnostics/rust.ts
new file mode 100644
index 000000000..d16576eb1
--- /dev/null
+++ b/editors/code/src/utils/diagnostics/rust.ts
@@ -0,0 +1,235 @@
+import * as path from 'path';
+import * as vscode from 'vscode';
+
+import SuggestedFix from './SuggestedFix';
+
+export enum SuggestionApplicability {
+    MachineApplicable = 'MachineApplicable',
+    HasPlaceholders = 'HasPlaceholders',
+    MaybeIncorrect = 'MaybeIncorrect',
+    Unspecified = 'Unspecified'
+}
+
+// Reference:
+// https://github.com/rust-lang/rust/blob/master/src/libsyntax/json.rs
+export interface RustDiagnosticSpan {
+    line_start: number;
+    line_end: number;
+    column_start: number;
+    column_end: number;
+    is_primary: boolean;
+    file_name: string;
+    label?: string;
+    suggested_replacement?: string;
+    suggestion_applicability?: SuggestionApplicability;
+}
+
+export interface RustDiagnostic {
+    spans: RustDiagnosticSpan[];
+    rendered: string;
+    message: string;
+    level: string;
+    code?: {
+        code: string;
+    };
+    children: RustDiagnostic[];
+}
+
+export interface MappedRustDiagnostic {
+    location: vscode.Location;
+    diagnostic: vscode.Diagnostic;
+    suggestedFixes: SuggestedFix[];
+}
+
+interface MappedRustChildDiagnostic {
+    related?: vscode.DiagnosticRelatedInformation;
+    suggestedFix?: SuggestedFix;
+    messageLine?: string;
+}
+
+/**
+ * Converts a Rust level string to a VsCode severity
+ */
+function mapLevelToSeverity(s: string): vscode.DiagnosticSeverity {
+    if (s === 'error') {
+        return vscode.DiagnosticSeverity.Error;
+    }
+    if (s.startsWith('warn')) {
+        return vscode.DiagnosticSeverity.Warning;
+    }
+    return vscode.DiagnosticSeverity.Information;
+}
+
+/**
+ * Converts a Rust span to a VsCode location
+ */
+function mapSpanToLocation(span: RustDiagnosticSpan): vscode.Location {
+    const fileName = path.join(vscode.workspace.rootPath!, span.file_name);
+    const fileUri = vscode.Uri.file(fileName);
+
+    const range = new vscode.Range(
+        new vscode.Position(span.line_start - 1, span.column_start - 1),
+        new vscode.Position(span.line_end - 1, span.column_end - 1)
+    );
+
+    return new vscode.Location(fileUri, range);
+}
+
+/**
+ * Converts a secondary Rust span to a VsCode related information
+ *
+ * If the span is unlabelled this will return `undefined`.
+ */
+function mapSecondarySpanToRelated(
+    span: RustDiagnosticSpan
+): vscode.DiagnosticRelatedInformation | undefined {
+    if (!span.label) {
+        // Nothing to label this with
+        return;
+    }
+
+    const location = mapSpanToLocation(span);
+    return new vscode.DiagnosticRelatedInformation(location, span.label);
+}
+
+/**
+ * Determines if diagnostic is related to unused code
+ */
+function isUnusedOrUnnecessary(rd: RustDiagnostic): boolean {
+    if (!rd.code) {
+        return false;
+    }
+
+    return [
+        'dead_code',
+        'unknown_lints',
+        'unused_attributes',
+        'unused_imports',
+        'unused_macros',
+        'unused_variables'
+    ].includes(rd.code.code);
+}
+
+/**
+ * Converts a Rust child diagnostic to a VsCode related information
+ *
+ * This can have three outcomes:
+ *
+ * 1. If this is no primary span this will return a `noteLine`
+ * 2. If there is a primary span with a suggested replacement it will return a
+ *    `codeAction`.
+ * 3. If there is a primary span without a suggested replacement it will return
+ *    a `related`.
+ */
+function mapRustChildDiagnostic(rd: RustDiagnostic): MappedRustChildDiagnostic {
+    const span = rd.spans.find(s => s.is_primary);
+
+    if (!span) {
+        // `rustc` uses these spanless children as a way to print multi-line
+        // messages
+        return { messageLine: rd.message };
+    }
+
+    // If we have a primary span use its location, otherwise use the parent
+    const location = mapSpanToLocation(span);
+
+    // We need to distinguish `null` from an empty string
+    if (span && typeof span.suggested_replacement === 'string') {
+        // Include our replacement in the title unless it's empty
+        const title = span.suggested_replacement
+            ? `${rd.message}: \`${span.suggested_replacement}\``
+            : rd.message;
+
+        return {
+            suggestedFix: new SuggestedFix(
+                title,
+                location,
+                span.suggested_replacement,
+                span.suggestion_applicability
+            )
+        };
+    } else {
+        const related = new vscode.DiagnosticRelatedInformation(
+            location,
+            rd.message
+        );
+
+        return { related };
+    }
+}
+
+/**
+ * Converts a Rust root diagnostic to VsCode form
+ *
+ * This flattens the Rust diagnostic by:
+ *
+ * 1. Creating a `vscode.Diagnostic` with the root message and primary span.
+ * 2. Adding any labelled secondary spans to `relatedInformation`
+ * 3. Categorising child diagnostics as either `SuggestedFix`es,
+ *    `relatedInformation` or additional message lines.
+ *
+ * If the diagnostic has no primary span this will return `undefined`
+ */
+export function mapRustDiagnosticToVsCode(
+    rd: RustDiagnostic
+): MappedRustDiagnostic | undefined {
+    const primarySpan = rd.spans.find(s => s.is_primary);
+    if (!primarySpan) {
+        return;
+    }
+
+    const location = mapSpanToLocation(primarySpan);
+    const secondarySpans = rd.spans.filter(s => !s.is_primary);
+
+    const severity = mapLevelToSeverity(rd.level);
+
+    const vd = new vscode.Diagnostic(location.range, rd.message, severity);
+
+    let source = 'rustc';
+    let code = rd.code && rd.code.code;
+    if (code) {
+        // See if this is an RFC #2103 scoped lint (e.g. from Clippy)
+        const scopedCode = code.split('::');
+        if (scopedCode.length === 2) {
+            [source, code] = scopedCode;
+        }
+    }
+
+    vd.source = source;
+    vd.code = code;
+    vd.relatedInformation = [];
+
+    for (const secondarySpan of secondarySpans) {
+        const related = mapSecondarySpanToRelated(secondarySpan);
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+    }
+
+    const suggestedFixes = [];
+    for (const child of rd.children) {
+        const { related, suggestedFix, messageLine } = mapRustChildDiagnostic(
+            child
+        );
+
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+        if (suggestedFix) {
+            suggestedFixes.push(suggestedFix);
+        }
+        if (messageLine) {
+            vd.message += `\n${messageLine}`;
+        }
+    }
+
+    if (isUnusedOrUnnecessary(rd)) {
+        vd.tags = [vscode.DiagnosticTag.Unnecessary];
+    }
+
+    return {
+        location,
+        diagnostic: vd,
+        suggestedFixes
+    };
+}
diff --git a/editors/code/src/utils/diagnostics/vscode.ts b/editors/code/src/utils/diagnostics/vscode.ts
new file mode 100644
index 000000000..d8b85b720
--- /dev/null
+++ b/editors/code/src/utils/diagnostics/vscode.ts
@@ -0,0 +1,14 @@
+import * as vscode from 'vscode';
+
+/** Compares two `vscode.Diagnostic`s for equality */
+export function areDiagnosticsEqual(
+    left: vscode.Diagnostic,
+    right: vscode.Diagnostic
+): boolean {
+    return (
+        left.source === right.source &&
+        left.severity === right.severity &&
+        left.range.isEqual(right.range) &&
+        left.message === right.message
+    );
+}