A solidity preprocessor and flattener CLI and library
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README.md

build status npm package

solpp

A preprocessor and flattener for Ethereum's Solidity source files.

solpp is designed specifically for Solidity, which means it actually understands some of Solidity's grammar and offers high-precision math and builtin functions suitable for use with Solidity's primitives.

Features

  • Flattens your source files for easy contract verification on etherscan.io by merging all naked imports.
  • Will even include URL imports, along with their dependencies.
  • Simple, practical language inspired by C preprocessor directives, python, and javascript.
  • Easily declare symbols and macro functions in your source file with #def directives.
  • #if/#elif/#else blocks for conditional code rendering.
  • #for blocks for repeating code.
  • Expand (substitute) with $(...) or evaluate with $$(...) symbols, macros, and expressions anywhere in your code.
  • All math is done in extremely high precision (up to120 digits) and can represent integers AND decimals.
  • Robust expression syntax with many useful builtin functions.
Please see the ChangeLog for breaking changes between versions.

Topics

Example

// solpp will inline this file and any of its dependencies.
import './MyLibrary.sol';
// solpp can also do the same with URLs!
import 'https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-solidity/v2.0.0/contracts/token/ERC20/ERC20.sol';

contract MyContract {
   // Define and use a symbol.
   // #def EIGHT_QUARTERS 8 / 4
   uint256 _var1 = $(EIGHT_QUARTERS); // -> uint256 _var1 = 8 / 4;
   // Evaluate a symbol as an expression. Note the double $.
   uint256 _var2 = $$(EIGHT_QUARTERS); // -> uint256 _var2 = 2;
   // We can even remove the symbol if we don't need it anymore.
   // #undef EIGHT_QUARTERS

   // Define and use a macro.
   // #def POW(a, b) a ** b
   // Here we expand then evaluate the symbol.
   uint256 _var3 = $(POW(2, 3)) + $$(POW(16, 0.5)); // -> uint256 _var3 = 2 ** 3 + 4;
   // Macros can call other macros and symbols during evaluation.
   // #def SQUARE(x) POW(x, 2)
   uint256 _var4 = $$(SQUARE(10)); // -> uint256 _var4 = 100;
   // You can also evaluate expressions inline.
   // Here we compute LOG(10) expressed as parts per million
   // using some builtin functions.
   uint256 _log10 = $$(int(log(10) * 1e6)); // -> uint256 _log10 = 2302585;
   // All math supports decimals. here we output sqrt(2) as a
   // decimal string with 16 digits of precision.
   string _sqrt2 = $$(quote(sd(2**0.5, 16))); // -> string _sqrt2 = "1.414213562373095";
   // We can even do bitwise operations on integers and output hex.
   bytes32 _bytes = $$(hex(int((2**0.5) * 1e18) << 8)); // -> bytes32 _bytes = 0x13a04bbdfdc9be8800;
   // Maybe we want to combine some strings.
   string _fullName = $$(quote(join(['Bob', 'Smith'], ' '))); // -> string _fullName = "Bob Smith";
   // Or do string interpolation.
   // #def GREETING(first, last) quote(`Hello, $(first} $(last}!`)
   string _fullName2 = $$(GREETING('Bob', 'Smith')) // -> string _fullName2 = "Hello, Bob Smith!";
   // Convert a private key to an address? Sure!
   // #def PRIV_KEY 0x563b99585e0709e3a7ac78b8957aa0f53bc874a86f288884d7ccafe3b9e9b934
   address _addr = $$(key2addr(PRIV_KEY)); // -> _addr = 0x86c0bfFbA7b505c82f1533aFe6C69A604c3e2870;

   function foo(uint256 x) pure returns (uint256) {
      // #if EXT_SYMBOL
      // If the symbol EXT_SYMBOL is defined externally or in a source file
      // as "truthy" (non-false, non-zero), this code will be rendered.
      return x * 100;
      // #else
      // Otherwise, this code will be rendered.
      return x / 100;
      // #endif
   }

   function bar(uint256 x) pure returns (uint256) {
     // Repeat code with a a for loop.
     return x /* #for V in range(1,4) */+ $$(V+1)/* #done */; // -> return x + 1 + 2 + 3;
   }
}

Installation

If your project scaffolding is node-based, you can install it as a development dependency inside your project directory. As a development dependency, you should be able to call solpp in a "scripts" entry in your project's package.json file.

To run the tool manually, you can use npx solpp from within your project directory.

# Install as a project development dependency with npm.
npm install -D solpp
# or if using yarn
yarn add -D solpp

If you want solpp to be accessible from anywhere in your filesystem, you'll need to install it globally.

# Install globally with npm.
npm install -g solpp
# or if using yarn
yarn global add solpp

Command Line Usage

CLI Options

Usage: solpp [options] <source-file>

Options:
   -v --version                 output the version number
   -o, --output <file>          write output to a file (instead of stdout)
   --no-flatten                 do not flatten (include) naked imports
   --no-pp                      disable the preprocessor (just flatten)
   -D, --define <name>[=value]  define a preprocessor symbol (can be repeated)
   --defs <file>                preprocessor definitions JS or JSON file
   --tolerant                   ignore missing imports when flattening
   -h, --help                   output usage information

Instructions

You should invoke solpp for the contract file that you want to preprocess. It will automatically include and preprocess all naked imports found within the file and subsequent files. Naked imports are of the form import "path/to/file";. Any other import scheme will be ignored.

solpp is not a compiler, so you will still need to compile the generated code yourself, via solc or a build pipeline like truffle.

If you are using a build pipeline such as truffle, you should keep your raw source files in a separate directory and run solpp to output code into the pipeline's source directory before compiling your project.

External Symbols

You can define preprocessor symbols inside source files using the #def directive or you can define them externally on the command line (with the -D flag) or in a JS/JSON file. The order of priority in which redundantly declared symbols override each other, from highest priority to lowest priority, is Source -> Command Line -> Definitions File.

A JSON definitions file is just a plain object such as:

{
   "MY_SYMBOL_1": 100,
   "MY_SYMBOL_2": true,
   "MY_SYMBOL_3": "48192.418291248",
   "MY_SYMBOL_4": "blah blah",
   "MY_SYMBOL_5": ['symbols', 'can', 'hold', 'lists']
}

If using a JS file, it will be imported as a nodejs module, so you must assign your object to module.exports. The advantage of using a JS file is you can define symbols as functions, which can be called from evaluations in your code.

Library Usage

If you require('solpp') into your nodejs project, you can use it programmatically. This allows solpp to be integrated into any pipeline.

The library exposes 3 functions, all of which return promises:

const solpp = require('solpp');

// Preprocess code. Returns processed code.
PROCESSED_CODE: String = await solpp.processCode(
   // The raw code to process.
   code: String,
   // Options object. All fields are optional.
   opts={
      // Dictionary of preprocessor symbols and functions
      defs: {...},
      // Unique name for the source unit (like a full path).
      name: String,
      // The current working directory.
      cwd: String,
      // Function to resolve imported files.
      resolver: Function(path, cwd, from),
      // Whether or not to collapse 2 or more empty lines. Defaults to true.
      collapseEmptyLines: Boolean,
      // Whether to ignore unresolved imports. Defaults to false.
      tolerant: Boolean,
      // Don't flatten/inline imports. Defaults to false.
      noFlatten: Boolean,
      // Disable the preprocessor. Defaults to false.
      noPreprocessor: Boolean
});

// Preprocess code in a file. Returns processed code.
PROCESSED_CODE: String = await solpp.processFile(
   // The path of the raw code file.
   path: String,
   // Same as in processCode().
   opts={...});

// The default resolver used when none is set.
// Will either resolve filesystem files or remote files (URLs).
// Returns an object.
{
   // The raw code in the file.
   code: String
   // A unique name for the file (usually just the full path or URL)
   name: String,
   // The parent directory (or URL path) of the file.
   cwd: String,
} = await solpp.resolver(
      // The import path. May be a relative or absolute path, or even a URL.
      path: String,
      // The current working directory, or parent URL path if coming from a remote file.
      cwd: String,
      // The name of the importing file.
      from: String
   );

Language Reference

Directive Syntax

All solpp directives are contained inside either line comments or block comments. This design is to maintain compatibility with existing Solidity editor highlighters. You can use line and block comment directives interchangeably. Line comment directives terminate at the end of the line, unless the line ends in a \ character, which allows you to continue the directive on the next immediate line comment.

Example

// Single line comment directive.
// #def LDEF All this text is the value of LDEF.

// A line comment directive spread across two lines.
// #def MULTILINE_LDEF If you start running out of room, you can continue \
// on the next line like so.

// Block comment directives are great in tight #for loops or #if blocks.
// This will render: uint256 fac5 = 1 * 2 * 3 * 4 * 5;
uint256 fac5 = 1/* #for i in range(2, 6) */ * $$(i)/* #done */;
bool maybe = /* #if SOME_SYMBOL */true/* #else */false;/* #endif */

Symbols

Symbols can be declared externally on the command line or in a definitions file, or from right within a source file with the #def directive. Symbols can take on arbitrary values: code snippets, expressions, strings, numbers (binary, hex, octal, decimals), booleans, and lists.

Once defined, symbols (and macros) can be expanded ($(...)) or evaluated ($$(...)) in your code. Symbols do not have to hold valid expressions, but only those that do can be evaluated.

If you no longer need a symbol, you can undefine it with the #undef directive.

Input

// Define a symbol
// #def MY_EXPR 1 + 1
// Expand it.
uint256 x = $(MY_EXPR);
// Now evaluate it.
uint256 y = $$(MY_EXPR);

// Remove this symbol.
// #undef MY_EXPR

Result

// Define a symbol
// Expand it.
uint256 x = 1 + 1;
// Now evaluate it.
uint256 y = 2;

// Remove this symbol.

Macros

Macros are similar to symbols except that they take some arguments, like a function. They can be defined externally in a (javascript) definitions file or from within your code also with the #def directive.

Expanding a macro will perform a substitution of the arguments across its contents. Evaluating a macro will evaluate its contents as an expression, just like calling a function. You can even call other macros or reference other symbols inside macros during evaluation. Like symbols, macros do not have to hold valid expressions, but only those that do can be evaluated.

If you no longer need a macro, you can undefine it with the #undef directive.

Input

// Define a macro
// #def MY_MACRO(x) (x / 2) + 1
// Expand it.
uint256 x = $(MY_MACRO(10));
// Evaluate it.
uint256 y = $$(MY_MACRO(10));

// Define a new macro that calls the other macro.
// #def OTHER_MACRO(x) MY_MACRO(x * 10)
// Evaluate it.
uint256 z = $$(OTHER_MACRO(8));

// Remove this macro.
// #undef OTHER_MACRO

Result

// Define a macro
// Expand it.
uint256 x = (10/2) + 1;
// Evaluate it.
uint256 y = 6;

// Define a new macro that calls the other macro.
// Evaluate it.
uint256 z = 41;

// Remove this macro.

Expansion

Expansion occurs whenever a $(...) block is encountered in regular code (i.e., not inside a comment or string literal). When expanding a symbol, the contents of that symbol are simply put in the place of the expansion block.

A similar result occurs when expanding a macro, except arguments will be substituted throughout the macro's contents.

Input

// Expanding a symbol.
// #def SYM_1 foo / 2
uint256 v = 1 + $(SYM_1);

// Expanding a macro.
// #def MACRO_1(x) x / 2
uint256 v2 = 1 + $(MACRO_1(100));

Result

// Expanding a symbol.
uint256 v = 1 + foo / 2;

// Expanding a macro.
uint256 v = 1 + 100 / 2;

Evaluation

Evaluation occurs whenever a $$(...) block is encountered in regular code (i.e., not inside a comment or string literal). When evaluating a symbol, the contents of that symbol are parsed and evaluated as an expression, with the ultimate result put in the place of the evaluation block. Macros work the same way, except they can accept arguments which will also be evaluated.

Macros and symbols call and refer to other macros, symbols, and builtins during evaluation.

If a macro or symbol does not contain a valid expression during an evaluation operation, an error will be raised. If a symbol is encountered that is undefined, it will take on the value of 0.

Input

// Evaluating a symbol.
// #def SYM_1 5 * 2
uint256 v = 1 + $$(SYM_1);

// Evaluating a macro.
// #def MACRO_1(x) x * 2
uint256 v2 = 1 + $$(MACRO_1(2));

// Macro calling another macro and referencing a symbol.
// #def SYM_2 2 ** 3
// #def MACRO_2(x) MACRO_1(x) + SYM_2
uint256 v3 = $$(MACRO_2(4));

Result

// Evaluating a symbol.
uint256 v = 1 + 10;

// Evaluating a macro.
uint256 v2 = 1 + 4;

// Macro calling another macro and referencing a symbol.
uint256 v3 = 16;

Inline Evaluation

You don't have to use symbols or macros in your evaluation blocks. You can put any valid expression inside of them as well.

Input

// Compute the sqrt of 2 as parts per million.
// Here we use the builtin function 'int' to make the result an integer.
uint256 sqrt2 = $$(int(2**0.5 * 1e6));

Result

// Compute the sqrt of 2 as parts per million.
// Here we use the builtin function 'int' to make the result an integer.
uint256 sqrt2 = 1414213;

If/Elif/Else Blocks

One of the most common uses of a preprocessor is conditional code generation. This is easily accomplished through the #if, #elif, #else, and #endif directives. Code between an #if/else/elif and #endif directive will only be rendered if the directive's condition evaluates to "truthy" (either true, non-zero, or a non-empty string). Conditions are normal preprocessor expressions, which can be as simple as a single value or a complex sequence of operations.

Blocks may also be nested, with inner blocks depending on outer blocks.

Input

// #if true
// This block will always render.
uint256 x = 100;
// #endif

// #if 0
// This block will never render
uint256 x = 200;
// #endif

// #if EXT_SYM_1
// This block will only render if EXT_SYM_1 is defined as truthy.
uint256 foo = 1;
// #elif EXT_SYM_2 == 'foobar'
// This Block will only render if EXT_SYM_1 is falsey (or undefined)
// AND EXT_SYM_1 is set to the string 'foobar'
uint256 foo = 2;
// #else
// This block will only render if the preceding two conditions fail.
uint256 foo = 3;
// #endif

Result (with EXT_SYM_2='foobar')

// This block will always render.
uint256 x = 100;

// This Block will only render if EXT_SYM_1 is falsey (or undefined)
// AND EXT_SYM_1 is set to the string 'foobar'
uint256 foo = 2;

For Loops

Another great use case for preprocessors is unrolling loops or generating constant values for an array. The #for directive can help you do all those things and more.

#for directives iterate over a list, either one you have explicity defined with the list operator ([...]) or from a list producing function function such as range(). #for directives have the syntax #for ITEM, IDX in LIST, which iterates over values and indices, or simply #for ITEM in LIST, if you only want to iterate over the values in a list.

Input

// Calculate the summation of 0...4
uint256 sum = 0;
// #for ITEM in range(1, 5)
sum += $$(ITEM);
// #done

Result

// Calculate the summation of 0...4
uint256 sum = 0;
sum += 1;
sum += 2;
sum += 3;
sum += 4;

While #for offers a lot of explicit control, when working with lists, (which the range() builtin returns), you might find a more concise solution by exploiting list builtin functions, such as map(), reduce(), and join().

Expressions

Preprocessor expressions are similar to javascript expressions, with many of the usual operations and precedence. All mathematical operations are done using high-precision (up to 120 significant digits) math, which can hold many more digits than the largest Solidity type (uint256).

It's worth noting that bitwise operations, however, will only operate on 256-bit integers, and will always result in a 256-bit unsigned integer. Attempting to perform a bitwise operation on a number with a decimal component will result in an error.

Operations

Operation Description
a + b Add a to b
a - b Subract b from a
a * b Multiple a with b
a / b Divide a by b
a % b Modulo of a with b
a ** b Raise a to b
~a 256-bit bitwise INVERT a
a & b 256-bit a bitwise AND b
a | b 256-bit a bitwise OR b
a ^ b 256-bit a bitwise XOR b
a << b 256-bit bitwise shift a left by b bits
a >> b 256-bit bitwise shift a right by b bits
!a logical NOT a
a || b logical a OR b
a && b logical a AND b
(...) Expression grouping (explicit precedence)
a ? b : c Ternary operator: return b if a is true, otherwise return c
foo(x, y, z) Call function/macro foo with arguments x, y, and z
id Evaluate the symbol id
[a, b, c] Create a list with values a, b, and c, which can be expressions
(a, b) => ... Define an anonymous (lambda) macro, useful for the map() and reduce() builtins
Literals

There are 3 types of literals: booleans, strings, and numbers. Internally, numbers are stored as decimal strings, so they do not lose precision.

Example Description
true true boolean
false false boolean
"foo" Double quoted string
'foo' Single quoted string
`foo $(bar}` Interpolated string (with bar expanded in place)
`foo $$(bar}` Interpolated string (with bar evaluated in place)
32 Positive integer number
-32 Negative integer number
32.55 Decimal number
1.5e5 Exponent notation number
0xa047 hexadecimal notation number
0b0101011 binary notation number
077414 octal notation number

Builtins

Many general-purpose and domain-specific builtin functions come already defined and can be called during evaluation.

Language Functions

Function Description
defined(x) Test whether the symbol x is defined
peek(x) Return the literal value of symbol x (does not evaluate the contents of x)
bool(x) Coerce x into a boolean
islist(x) Check if x is a list

Numerical Functions

Function Description
min(a, b) Take the minimum of a and b
max(a, b) Take the maximum of a and b
clamp(x, lo, hi) Clamp x to be within lo and hi, inclusive
abs(x) Take the absolute value of x
sqrt(x) Get the square root of x, same as doing x**0.5
log(x) Take the natural logarithm of x
log(x, b) Take the logarithm of x with base b
exp(y) Raise the mathematical constant e to y
sign(x) Get the sign of x (either -1, 0, or 1)
sd(x) Get the number of significant digits in the number x
sd(x, n) Return a number which is x with n significant digits
dp(x) Get the number of decimal places in the number x
dp(x, n) Return a number which is x with n decimal places
round(x) Round x to a signed integer
int(x) Truncate x to a signed integer
uint(x) Truncate x to an positive integer
int8(x) Truncate x to a signed 8-bit integer
uint8(x) Truncate x to an positive 8-bit integer
int16(x) Truncate x to a signed 16-bit integer
uint16(x) Truncate x to an positive 16-bit integer
int32(x) Truncate x to a signed 32-bit integer
uint32(x) Truncate x to an positive 32-bit integer
int64(x) Truncate x to a signed 64-bit integer
uint64(x) Truncate x to an positive 64-bit integer
int128(x) Truncate x to a signed 128-bit integer
uint128(x) Truncate x to an positive 128-bit integer
int256(x) Truncate x to a signed 256-bit integer
uint256(x) Truncate x to an positive 256-bit integer
hex(x) Encode x as a hexadecimal
hex(x, n) Encode x as a hexadecimal, padding or truncating to n bytes. If n is negative, n will be right padded/truncated.
decimal(x) Encode x as a decimal

String Functions

Function Description
len(x) Get the length of string x
concat(...) Concatenates all arguments into a single string.
quote(x) Turn x into a quoted string.
unquote(x) Remove quotes from a quoted string x.
strhex(x) Return the utf-8 hex of a string x.
uppercase(x) Uppercase the string x.
lowercase(x) Lowercase the string x.
camelcase(x) Camelcase the string x.
capitalize(x) capitalize the string x.
repeat(s, n) Repeat the string s n times.

List Functions

Function Description
islist(x) Check if x is a list
len(x) Get the length of list x
range(end) Create a list of numbers from 0 to end (exclusive) with step size 1
range(start, end, step=1) Create a list of numbers from start to end (exclusive) with step size step
filled(len, value=0) Create a len length list filled with value
concat(...) Combines a series of lists into one.
sum(x) Returns the sum of all values in x.
join(a, sep='') Join list a into a string with separator sep
map(a, fn) Create a list where each item in a is run through the function/macro fn. If fn can take two arguments, the index of the item will be passed as the 2nd argument.
reduce(a, fn, initial=0) Run items in the list a through the function/macro fn, which takes 2-3 arguments (total, value, [index]) and returns the new total.

Ethereum Functions

Function Description
keccak256(...) Compute the keccak256 hash of all arguments.
key2addr(k) Get the address associated with private key k

Constants

Name Description
E The mathematical constant e
PI The mathematical constant π
__line The line number of the expression
__indent The indentation of the expression (string of whitespaces leading up to the expression