1 files changed, 220 insertions, 0 deletions

diff --git a/editors/code/src/utils/rust_diagnostics.ts b/editors/code/src/utils/rust_diagnostics.ts
new file mode 100644
index 000000000..7d8cc0e0b
--- /dev/null
+++ b/editors/code/src/utils/rust_diagnostics.ts
@@ -0,0 +1,220 @@
+import * as path from 'path';
+import * as vscode from 'vscode';
+
+// 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?:
+        | 'MachineApplicable'
+        | 'HasPlaceholders'
+        | 'MaybeIncorrect'
+        | 'Unspecified';
+}
+
+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;
+    codeActions: vscode.CodeAction[];
+}
+
+interface MappedRustChildDiagnostic {
+    related?: vscode.DiagnosticRelatedInformation;
+    codeAction?: vscode.CodeAction;
+    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;
+    }
+
+    const { code } = rd.code;
+    return code.startsWith('unused_') || code === 'dead_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') {
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(location.uri, location.range, span.suggested_replacement);
+
+        // Include our replacement in the label unless it's empty
+        const title = span.suggested_replacement
+            ? `${rd.message}: \`${span.suggested_replacement}\``
+            : rd.message;
+
+        const codeAction = new vscode.CodeAction(
+            title,
+            vscode.CodeActionKind.QuickFix
+        );
+
+        codeAction.edit = edit;
+        codeAction.isPreferred =
+            span.suggestion_applicability === 'MachineApplicable';
+
+        return { codeAction };
+    } 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 Quick Fix actions,
+ *    `relatedInformation` or additional message lines.
+ *
+ * If the diagnostic has no primary span this will return `undefined`
+ */
+export function mapRustDiagnosticToVsCode(
+    rd: RustDiagnostic
+): MappedRustDiagnostic | undefined {
+    const codeActions = [];
+
+    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);
+
+    vd.source = 'rustc';
+    vd.code = rd.code ? rd.code.code : undefined;
+    vd.relatedInformation = [];
+
+    for (const secondarySpan of secondarySpans) {
+        const related = mapSecondarySpanToRelated(secondarySpan);
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+    }
+
+    for (const child of rd.children) {
+        const { related, codeAction, messageLine } = mapRustChildDiagnostic(
+            child
+        );
+
+        if (related) {
+            vd.relatedInformation.push(related);
+        }
+        if (codeAction) {
+            codeActions.push(codeAction);
+        }
+        if (messageLine) {
+            vd.message += `\n${messageLine}`;
+        }
+    }
+
+    if (isUnusedOrUnnecessary(rd)) {
+        vd.tags = [vscode.DiagnosticTag.Unnecessary];
+    }
+
+    return {
+        location,
+        diagnostic: vd,
+        codeActions
+    };
+}