blockly/core/generator.ts

/**
 * @license
 * Copyright 2012 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * Utility functions for generating executable code from
 * Blockly code.
 *
 * @class
 */
import * as goog from '../closure/goog/goog.js';
goog.declareModuleId('Blockly.CodeGenerator');

import type {Block} from './block.js';
import * as common from './common.js';
import {Names, NameType} from './names.js';
import type {Workspace} from './workspace.js';
import {warn} from './utils/deprecation.js';

/**
 * Type declaration for per-block-type generator functions.
 *
 * @see {@link https://developers.google.com/blockly/guides/create-custom-blocks/generating-code}
 * @param block The Block instance to generate code for.
 * @param genearator The CodeGenerator calling the function.
 * @returns A string containing the generated code (for statement blocks),
 *     or a [code, precedence] tuple (for value/expression blocks), or
 *     null if no code should be emitted for block.
 */
export type BlockGenerator = (
  block: Block,
  generator: CodeGenerator
) => [string, number] | string | null;

/**
 * Class for a code generator that translates the blocks into a language.
 */
export class CodeGenerator {
  name_: string;

  /** A dictionary of block generator functions keyed by block type. */
  forBlock: {[type: string]: BlockGenerator} = Object.create(null);

  /**
   * This is used as a placeholder in functions defined using
   * CodeGenerator.provideFunction_.  It must not be legal code that could
   * legitimately appear in a function definition (or comment), and it must
   * not confuse the regular expression parser.
   */
  protected FUNCTION_NAME_PLACEHOLDER_ = '{leCUI8hutHZI4480Dc}';
  FUNCTION_NAME_PLACEHOLDER_REGEXP_: RegExp;

  /**
   * Arbitrary code to inject into locations that risk causing infinite loops.
   * Any instances of '%1' will be replaced by the block ID that failed.
   * E.g. `  checkTimeout(%1);\n`
   */
  INFINITE_LOOP_TRAP: string | null = null;

  /**
   * Arbitrary code to inject before every statement.
   * Any instances of '%1' will be replaced by the block ID of the statement.
   * E.g. `highlight(%1);\n`
   */
  STATEMENT_PREFIX: string | null = null;

  /**
   * Arbitrary code to inject after every statement.
   * Any instances of '%1' will be replaced by the block ID of the statement.
   * E.g. `highlight(%1);\n`
   */
  STATEMENT_SUFFIX: string | null = null;

  /**
   * The method of indenting.  Defaults to two spaces, but language generators
   * may override this to increase indent or change to tabs.
   */
  INDENT = '  ';

  /**
   * Maximum length for a comment before wrapping.  Does not account for
   * indenting level.
   */
  COMMENT_WRAP = 60;

  /** List of outer-inner pairings that do NOT require parentheses. */
  ORDER_OVERRIDES: number[][] = [];

  /**
   * Whether the init method has been called.
   * Generators that set this flag to false after creation and true in init
   * will cause blockToCode to emit a warning if the generator has not been
   * initialized. If this flag is untouched, it will have no effect.
   */
  isInitialized: boolean | null = null;

  /** Comma-separated list of reserved words. */
  protected RESERVED_WORDS_ = '';

  /** A dictionary of definitions to be printed before the code. */
  protected definitions_: {[key: string]: string} = Object.create(null);

  /**
   * A dictionary mapping desired function names in definitions_ to actual
   * function names (to avoid collisions with user functions).
   */
  protected functionNames_: {[key: string]: string} = Object.create(null);

  /** A database of variable and procedure names. */
  protected nameDB_?: Names = undefined;

  /** @param name Language name of this generator. */
  constructor(name: string) {
    this.name_ = name;

    this.FUNCTION_NAME_PLACEHOLDER_REGEXP_ = new RegExp(
      this.FUNCTION_NAME_PLACEHOLDER_,
      'g'
    );
  }

  /**
   * Generate code for all blocks in the workspace to the specified language.
   *
   * @param workspace Workspace to generate code from.
   * @returns Generated code.
   */
  workspaceToCode(workspace?: Workspace): string {
    if (!workspace) {
      // Backwards compatibility from before there could be multiple workspaces.
      console.warn(
        'No workspace specified in workspaceToCode call.  Guessing.'
      );
      workspace = common.getMainWorkspace();
    }
    const code = [];
    this.init(workspace);
    const blocks = workspace.getTopBlocks(true);
    for (let i = 0, block; (block = blocks[i]); i++) {
      let line = this.blockToCode(block);
      if (Array.isArray(line)) {
        // Value blocks return tuples of code and operator order.
        // Top-level blocks don't care about operator order.
        line = line[0];
      }
      if (line) {
        if (block.outputConnection) {
          // This block is a naked value.  Ask the language's code generator if
          // it wants to append a semicolon, or something.
          line = this.scrubNakedValue(line);
          if (this.STATEMENT_PREFIX && !block.suppressPrefixSuffix) {
            line = this.injectId(this.STATEMENT_PREFIX, block) + line;
          }
          if (this.STATEMENT_SUFFIX && !block.suppressPrefixSuffix) {
            line = line + this.injectId(this.STATEMENT_SUFFIX, block);
          }
        }
        code.push(line);
      }
    }
    // Blank line between each section.
    let codeString = code.join('\n');
    codeString = this.finish(codeString);
    // Final scrubbing of whitespace.
    codeString = codeString.replace(/^\s+\n/, '');
    codeString = codeString.replace(/\n\s+$/, '\n');
    codeString = codeString.replace(/[ \t]+\n/g, '\n');
    return codeString;
  }

  // The following are some helpful functions which can be used by multiple

  // languages.

  /**
   * Prepend a common prefix onto each line of code.
   * Intended for indenting code or adding comment markers.
   *
   * @param text The lines of code.
   * @param prefix The common prefix.
   * @returns The prefixed lines of code.
   */
  prefixLines(text: string, prefix: string): string {
    return prefix + text.replace(/(?!\n$)\n/g, '\n' + prefix);
  }

  /**
   * Recursively spider a tree of blocks, returning all their comments.
   *
   * @param block The block from which to start spidering.
   * @returns Concatenated list of comments.
   */
  allNestedComments(block: Block): string {
    const comments = [];
    const blocks = block.getDescendants(true);
    for (let i = 0; i < blocks.length; i++) {
      const comment = blocks[i].getCommentText();
      if (comment) {
        comments.push(comment);
      }
    }
    // Append an empty string to create a trailing line break when joined.
    if (comments.length) {
      comments.push('');
    }
    return comments.join('\n');
  }

  /**
   * Generate code for the specified block (and attached blocks).
   * The generator must be initialized before calling this function.
   *
   * @param block The block to generate code for.
   * @param opt_thisOnly True to generate code for only this statement.
   * @returns For statement blocks, the generated code.
   *     For value blocks, an array containing the generated code and an
   * operator order value.  Returns '' if block is null.
   */
  blockToCode(
    block: Block | null,
    opt_thisOnly?: boolean
  ): string | [string, number] {
    if (this.isInitialized === false) {
      console.warn(
        'CodeGenerator init was not called before blockToCode was called.'
      );
    }
    if (!block) {
      return '';
    }
    if (!block.isEnabled()) {
      // Skip past this block if it is disabled.
      return opt_thisOnly ? '' : this.blockToCode(block.getNextBlock());
    }
    if (block.isInsertionMarker()) {
      // Skip past insertion markers.
      return opt_thisOnly ? '' : this.blockToCode(block.getChildren(false)[0]);
    }

    // Look up block generator function in dictionary - but fall back
    // to looking up on this if not found, for backwards compatibility.
    let func = this.forBlock[block.type];
    if (!func && (this as any)[block.type]) {
      warn(
        'block generator functions on CodeGenerator objects',
        '10.0',
        '11.0',
        'the .forBlock[blockType] dictionary'
      );
      func = (this as any)[block.type];
    }
    if (typeof func !== 'function') {
      throw Error(
        `${this.name_} generator does not know how to generate code` +
          `for block type "${block.type}".`
      );
    }
    // First argument to func.call is the value of 'this' in the generator.
    // Prior to 24 September 2013 'this' was the only way to access the block.
    // The current preferred method of accessing the block is through the second
    // argument to func.call, which becomes the first parameter to the
    // generator.
    let code = func.call(block, block, this);
    if (Array.isArray(code)) {
      // Value blocks return tuples of code and operator order.
      if (!block.outputConnection) {
        throw TypeError('Expecting string from statement block: ' + block.type);
      }
      return [this.scrub_(block, code[0], opt_thisOnly), code[1]];
    } else if (typeof code === 'string') {
      if (this.STATEMENT_PREFIX && !block.suppressPrefixSuffix) {
        code = this.injectId(this.STATEMENT_PREFIX, block) + code;
      }
      if (this.STATEMENT_SUFFIX && !block.suppressPrefixSuffix) {
        code = code + this.injectId(this.STATEMENT_SUFFIX, block);
      }
      return this.scrub_(block, code, opt_thisOnly);
    } else if (code === null) {
      // Block has handled code generation itself.
      return '';
    }
    throw SyntaxError('Invalid code generated: ' + code);
  }

  /**
   * Generate code representing the specified value input.
   *
   * @param block The block containing the input.
   * @param name The name of the input.
   * @param outerOrder The maximum binding strength (minimum order value) of any
   *     operators adjacent to "block".
   * @returns Generated code or '' if no blocks are connected or the specified
   *     input does not exist.
   */
  valueToCode(block: Block, name: string, outerOrder: number): string {
    if (isNaN(outerOrder)) {
      throw TypeError('Expecting valid order from block: ' + block.type);
    }
    const targetBlock = block.getInputTargetBlock(name);
    if (!targetBlock) {
      return '';
    }
    const tuple = this.blockToCode(targetBlock);
    if (tuple === '') {
      // Disabled block.
      return '';
    }
    // Value blocks must return code and order of operations info.
    // Statement blocks must only return code.
    if (!Array.isArray(tuple)) {
      throw TypeError(
        `Expecting tuple from value block: ${targetBlock.type} See ` +
          `developers.google.com/blockly/guides/create-custom-blocks/generating-code ` +
          `for more information`
      );
    }
    let code = tuple[0];
    const innerOrder = tuple[1];
    if (isNaN(innerOrder)) {
      throw TypeError(
        'Expecting valid order from value block: ' + targetBlock.type
      );
    }
    if (!code) {
      return '';
    }

    // Add parentheses if needed.
    let parensNeeded = false;
    const outerOrderClass = Math.floor(outerOrder);
    const innerOrderClass = Math.floor(innerOrder);
    if (outerOrderClass <= innerOrderClass) {
      if (
        outerOrderClass === innerOrderClass &&
        (outerOrderClass === 0 || outerOrderClass === 99)
      ) {
        // Don't generate parens around NONE-NONE and ATOMIC-ATOMIC pairs.
        // 0 is the atomic order, 99 is the none order.  No parentheses needed.
        // In all known languages multiple such code blocks are not order
        // sensitive.  In fact in Python ('a' 'b') 'c' would fail.
      } else {
        // The operators outside this code are stronger than the operators
        // inside this code.  To prevent the code from being pulled apart,
        // wrap the code in parentheses.
        parensNeeded = true;
        // Check for special exceptions.
        for (let i = 0; i < this.ORDER_OVERRIDES.length; i++) {
          if (
            this.ORDER_OVERRIDES[i][0] === outerOrder &&
            this.ORDER_OVERRIDES[i][1] === innerOrder
          ) {
            parensNeeded = false;
            break;
          }
        }
      }
    }
    if (parensNeeded) {
      // Technically, this should be handled on a language-by-language basis.
      // However all known (sane) languages use parentheses for grouping.
      code = '(' + code + ')';
    }
    return code;
  }

  /**
   * Generate a code string representing the blocks attached to the named
   * statement input. Indent the code.
   * This is mainly used in generators. When trying to generate code to evaluate
   * look at using workspaceToCode or blockToCode.
   *
   * @param block The block containing the input.
   * @param name The name of the input.
   * @returns Generated code or '' if no blocks are connected.
   */
  statementToCode(block: Block, name: string): string {
    const targetBlock = block.getInputTargetBlock(name);
    let code = this.blockToCode(targetBlock);
    // Value blocks must return code and order of operations info.
    // Statement blocks must only return code.
    if (typeof code !== 'string') {
      throw TypeError(
        'Expecting code from statement block: ' +
          (targetBlock && targetBlock.type)
      );
    }
    if (code) {
      code = this.prefixLines(code, this.INDENT);
    }
    return code;
  }

  /**
   * Add an infinite loop trap to the contents of a loop.
   * Add statement suffix at the start of the loop block (right after the loop
   * statement executes), and a statement prefix to the end of the loop block
   * (right before the loop statement executes).
   *
   * @param branch Code for loop contents.
   * @param block Enclosing block.
   * @returns Loop contents, with infinite loop trap added.
   */
  addLoopTrap(branch: string, block: Block): string {
    if (this.INFINITE_LOOP_TRAP) {
      branch =
        this.prefixLines(
          this.injectId(this.INFINITE_LOOP_TRAP, block),
          this.INDENT
        ) + branch;
    }
    if (this.STATEMENT_SUFFIX && !block.suppressPrefixSuffix) {
      branch =
        this.prefixLines(
          this.injectId(this.STATEMENT_SUFFIX, block),
          this.INDENT
        ) + branch;
    }
    if (this.STATEMENT_PREFIX && !block.suppressPrefixSuffix) {
      branch =
        branch +
        this.prefixLines(
          this.injectId(this.STATEMENT_PREFIX, block),
          this.INDENT
        );
    }
    return branch;
  }

  /**
   * Inject a block ID into a message to replace '%1'.
   * Used for STATEMENT_PREFIX, STATEMENT_SUFFIX, and INFINITE_LOOP_TRAP.
   *
   * @param msg Code snippet with '%1'.
   * @param block Block which has an ID.
   * @returns Code snippet with ID.
   */
  injectId(msg: string, block: Block): string {
    const id = block.id.replace(/\$/g, '$$$$'); // Issue 251.
    return msg.replace(/%1/g, "'" + id + "'");
  }

  /**
   * Add one or more words to the list of reserved words for this language.
   *
   * @param words Comma-separated list of words to add to the list.
   *     No spaces.  Duplicates are ok.
   */
  addReservedWords(words: string) {
    this.RESERVED_WORDS_ += words + ',';
  }

  /**
   * Define a developer-defined function (not a user-defined procedure) to be
   * included in the generated code.  Used for creating private helper
   * functions. The first time this is called with a given desiredName, the code
   * is saved and an actual name is generated.  Subsequent calls with the same
   * desiredName have no effect but have the same return value.
   *
   * It is up to the caller to make sure the same desiredName is not
   * used for different helper functions (e.g. use "colourRandom" and
   * "listRandom", not "random").  There is no danger of colliding with reserved
   * words, or user-defined variable or procedure names.
   *
   * The code gets output when CodeGenerator.finish() is called.
   *
   * @param desiredName The desired name of the function (e.g. mathIsPrime).
   * @param code A list of statements or one multi-line code string.  Use '  '
   *     for indents (they will be replaced).
   * @returns The actual name of the new function.  This may differ from
   *     desiredName if the former has already been taken by the user.
   */
  protected provideFunction_(
    desiredName: string,
    code: string[] | string
  ): string {
    if (!this.definitions_[desiredName]) {
      const functionName = this.nameDB_!.getDistinctName(
        desiredName,
        NameType.PROCEDURE
      );
      this.functionNames_[desiredName] = functionName;
      if (Array.isArray(code)) {
        code = code.join('\n');
      }
      let codeText = code
        .trim()
        .replace(this.FUNCTION_NAME_PLACEHOLDER_REGEXP_, functionName);
      // Change all '  ' indents into the desired indent.
      // To avoid an infinite loop of replacements, change all indents to '\0'
      // character first, then replace them all with the indent.
      // We are assuming that no provided functions contain a literal null char.
      let oldCodeText;
      while (oldCodeText !== codeText) {
        oldCodeText = codeText;
        codeText = codeText.replace(/^(( {2})*) {2}/gm, '$1\0');
      }
      codeText = codeText.replace(/\0/g, this.INDENT);
      this.definitions_[desiredName] = codeText;
    }
    return this.functionNames_[desiredName];
  }

  /**
   * Hook for code to run before code generation starts.
   * Subclasses may override this, e.g. to initialise the database of variable
   * names.
   *
   * @param _workspace Workspace to generate code from.
   */
  init(_workspace: Workspace) {
    // Optionally override
    // Create a dictionary of definitions to be printed before the code.
    this.definitions_ = Object.create(null);
    // Create a dictionary mapping desired developer-defined function names in
    // definitions_ to actual function names (to avoid collisions with
    // user-defined procedures).
    this.functionNames_ = Object.create(null);
  }

  /**
   * Common tasks for generating code from blocks.  This is called from
   * blockToCode and is called on every block, not just top level blocks.
   * Subclasses may override this, e.g. to generate code for statements
   * following the block, or to handle comments for the specified block and any
   * connected value blocks.
   *
   * @param _block The current block.
   * @param code The code created for this block.
   * @param _opt_thisOnly True to generate code for only this statement.
   * @returns Code with comments and subsequent blocks added.
   */
  protected scrub_(
    _block: Block,
    code: string,
    _opt_thisOnly?: boolean
  ): string {
    // Optionally override
    return code;
  }

  /**
   * Hook for code to run at end of code generation.
   * Subclasses may override this, e.g. to prepend the generated code with
   * import statements or variable definitions.
   *
   * @param code Generated code.
   * @returns Completed code.
   */
  finish(code: string): string {
    // Optionally override
    // Clean up temporary data.
    this.definitions_ = Object.create(null);
    this.functionNames_ = Object.create(null);
    return code;
  }

  /**
   * Naked values are top-level blocks with outputs that aren't plugged into
   * anything.
   * Subclasses may override this, e.g. if their language does not allow
   * naked values.
   *
   * @param line Line of generated code.
   * @returns Legal line of code.
   */
  scrubNakedValue(line: string): string {
    // Optionally override
    return line;
  }
}