Compilation error when less than operator is attached with the variable on the left.

[purusang]

Steps to Reproduce Issue

With the following code you may encounter an error on sui move build. The best way to reproduce is to use '<' sign attached with the variable on its left inside if or while.
I have tested it multiple times and got the same error.

My code snippet:

        while(sub_len>0) {    // 0 or 1?
            hash_value = poseidon::poseidon_bn254(&vector[hash_value, hash_value]);
            let mut j = sub_len/2;
            while(j< sub_len){
            //     // let mut e: u256 = vector::borrow_mut<u256>( tree_array, j);
            //     j = j+ 1;
            };
            
        };

Expected Result

Compilation should have been successful.

Actual Result

error[E01002]: unexpected token
┌─ ./sources/merkle_tree.move:47:29
│
47 │ while(j< sub_len){
│ ^
│ │
│ Unexpected ')'
│ Expected ',' or '>'

error[E01002]: unexpected token
┌─ ./sources/merkle_tree.move:47:30
│
47 │ while(j< sub_len){
│ - ^ Expected '>'
│ │
│ To match this '<'

error[E01002]: unexpected token
┌─ ./sources/merkle_tree.move:50:14
│
50 │ };
│ ^
│ │
│ Unexpected ';'
│ Expected ')'

error[E01002]: unexpected token
┌─ ./sources/merkle_tree.move:52:10
│
52 │ };
│ ^
│ │
│ Unexpected ';'
│ Expected a module member: 'spec', 'use', 'friend', 'const', 'fun', 'struct', or 'enum'

Failed to build Move modules: Compilation error.

System Information

• OS: macos
• Compiler: sui-move 1.23.1-4dbcf811ab

[stefan-mysten]

Thanks for reporting this @purusang! This is a known issue and it has to do with lexing and parsing the code. The team is aware of this and added it to the backlog.

In the meantime, please use spaces before and after the < character to avoid this parsing error.

 while( j < sub_len ){ 

[purusang]

Thank you too @stefan-mysten