internal/tsetse/failure.ts

import * as ts from 'typescript';

/**
 * A Tsetse check Failure is almost identical to a Diagnostic from TypeScript
 * except that:
 * (1) The error code is defined by each individual Tsetse rule.
 * (2) The optional `source` property is set to `Tsetse` so the host (VS Code
 * for instance) would use that to indicate where the error comes from.
 * (3) There's an optional suggestedFix field.
 */
export class Failure {
  constructor(
      private readonly sourceFile: ts.SourceFile,
      private readonly start: number, private readonly end: number,
      private readonly failureText: string, private readonly code: number,
      private readonly suggestedFix?: Fix) {}

  /**
   * This returns a structure compatible with ts.Diagnostic, but with added
   * fields, for convenience and to support suggested fixes.
   */
  toDiagnostic(): DiagnosticWithFix {
    return {
      file: this.sourceFile,
      start: this.start,
      end: this.end,  // Not in ts.Diagnostic, but always useful for
                      // start-end-using systems.
      length: this.end - this.start,
      messageText: this.failureText,
      category: ts.DiagnosticCategory.Error,
      code: this.code,
      // source is the name of the plugin.
      source: 'Tsetse',
      fix: this.suggestedFix
    };
  }

  /**
   * Same as toDiagnostic, but include the fix in the message, so that systems
   * that don't support displaying suggested fixes can still surface that
   * information. This assumes the diagnostic message is going to be presented
   * within the context of the problematic code
   */
  toDiagnosticWithStringifiedFix(): DiagnosticWithFix {
    const diagnostic = this.toDiagnostic();
    if (this.suggestedFix) {
      diagnostic.messageText += ' ' + this.fixToReadableStringInContext();
    }
    return diagnostic;
  }

  toString(): string {
    return `{ sourceFile:${
        this.sourceFile ? this.sourceFile.fileName : 'unknown'}, start:${
        this.start}, end:${this.end}, fix:${fixToString(this.suggestedFix)} }`;
  }


  /**
   * Stringifies a `Fix`, in a way that makes sense when presented alongside the
   * finding. This is a heuristic, obviously.
   */
  fixToReadableStringInContext() {
    if (!this.suggestedFix) return '';  // no changes, nothing to state.
    const f: Fix = this.suggestedFix;
    let fixText = '';

    for (const c of f.changes) {
      // Insertion.
      if (c.start === c.end) {
        // Try to see if that's an import.
        if (c.replacement.indexOf('import') !== -1) {
          fixText += `- Add new import: ${c.replacement}\n`;
        } else {
          // Insertion that's not a full import. This should rarely happen in
          // our context, and we don't have a great message for these.
          // For instance, this could be the addition of a new symbol in an
          // existing import (`import {foo}` becoming `import {foo, bar}`).
          fixText += `- Insert ${this.readableRange(c.start, c.end)}: ${
              c.replacement}\n`;
        }
      } else if (c.start === this.start && c.end === this.end) {
        // We assume the replacement is the main part of the fix, so put that
        // individual change first in `fixText`.
        fixText = `- Replace the full match with: ${c.replacement}\n` + fixText;
      } else {
        // Fallback case: Use a numerical range to specify a replacement. In
        // general, falling through in this case should be avoided, as it's not
        // really readable without an IDE (the range can be outside of the
        // matched code).
        fixText = `- Replace ${this.readableRange(c.start, c.end)} with: ` +
            `${c.replacement}\n${fixText}`;
      }
    }

    return 'Suggested fix:\n' + fixText.trim();
  }

  // TS indexes from 0 both ways, but tooling generally indexes from 1 for both
  // lines and columns. The translation is done here.
  readableRange(from: number, to: number) {
    const lcf = this.sourceFile.getLineAndCharacterOfPosition(from);
    const lct = this.sourceFile.getLineAndCharacterOfPosition(to);
    if (lcf.line === lct.line) {
      if (lcf.character === lct.character) {
        return `at line ${lcf.line + 1}, char ${lcf.character + 1}`;
      }
      return `line ${lcf.line + 1}, from char ${lcf.character + 1} to ${
          lct.character + 1}`;
    } else {
      return `from line ${lcf.line + 1}, char ${lcf.character + 1} to line ${
          lct.line + 1}, char ${lct.character + 1}`;
    }
  }
}

/**
 * A `Fix` is a potential repair to the associated `Failure`.
 */
export interface Fix {
  /**
   * The individual text replacements composing that fix.
   */
  changes: IndividualChange[],
}

/**
 * An individual text replacement/insertion in a source file. Used as part of a
 * `Fix`.
 */
export interface IndividualChange {
  sourceFile: ts.SourceFile, start: number, end: number, replacement: string
}

/**
 * A ts.Diagnostic that might include a `Fix`, and with an added `end` field for
 * convenience.
 */
export interface DiagnosticWithFix extends ts.Diagnostic {
  end: number;
  fix?: Fix;
}

/**
 * Stringifies a `Fix`, replacing the `ts.SourceFile` with the matching
 * filename.
 */
export function fixToString(f?: Fix) {
  if (!f) return 'undefined';
  return '{' + JSON.stringify(f.changes.map(ic => {
    return {
      start: ic.start,
      end: ic.end,
      replacement: ic.replacement,
      fileName: ic.sourceFile.fileName
    };
  })) +
      '}'
}