CRIT ISSUE with LESS4J scope

[twhoff]

Scope inheritance in LESS4J is not working as intended in LESS.

Basically, child mixins inherit global scope OR parent scope before any operations on variables take place.

Simple example

In the following code @width is inherited from the global scope in .fluid-col().

The .calculate() mixin then converts the number to a valid percentage, and as @width is not explicitly set within the scope of .fluid-col(), the unlocked @width variable should override the inherited one, as is specified in LESS documentation:

Variables and mixins defined in a mixin are visible and can be used in caller's scope. There is only one exception, a variable is not copied if the caller contains a variable with the same name (that includes variables defined by another mixin call). Only variables present in callers local scope are protected. Variables inherited from parent scopes are overridden.

The overridden @width variable should now be inherited by the .inner-scope-test() mixin, however, in LESS4J this is not the case.

/* Scope test */

// Global scope
@width: 1/3;

// Caller
.test {
    .fluid-col();
}

// Mixin
.fluid-col() {
    // @width should be changed to 33.33333333%
    .calculate(@width);
    width: @width;

    .inner-scope-test();
    .inner-scope-test() {
        width2: @width;
    }
}

// Operator
.calculate(@arg) {
    @width: unit(@arg * 100, %);
}

Correct output from LESS compiler

• width2 shows % value

/* Scope test */
.test {
  width: 33.33333333%;
  width2: 33.33333333%;
}

Incorrect output from LESS4J compiler

• width2 shows numeric value
• should also note precision of decimal places is 16 vs 8 in LESS
• further, comment is not visible in LESS4J output

.test {
  width: 33.33333333333333%;
  width2: 0.3333333333333333;
}

Workaround
Passing the operated variable as a parameter to the inner mixin produces the correct result, however, this is less than ideal when you are dealing with multiple parameters which you then need to keep track of manually.

/* Scope test */

// Global scope
@width: 1/3;

// Caller
.test {
    .fluid-col();
}

// Mixin
.fluid-col() {
    // @width should be changed to 33.33333333%
    .calculate(@width);
    width: @width;

    .inner-scope-test(@width);
    .inner-scope-test(@width) {
        width2: @width;
    }
}

// Operator
.calculate(@arg) {
    @width: unit(@arg * 100, %);
}

Output

.test {
  width: 33.33333333333333%;
  width2: 33.33333333333333%;
}

[SomMeri]

Note to self: The issue is caused by these lines:

less4j/src/main/java/com/github/sommeri/less4j/core/compiler/stages/MixinsRulesetsSolver.java

Lines 139 to 144 in bca5cb2

	ScopeView mixinWorkingScope = scopeManipulation.joinIfIndependent(callerScope, mixinScope);
	// it the mixin calls itself recursively, each copy should work on
	// independent copy of local data
	// that is matters mostly for scope placeholders - if both close
	// placeholders in same copy error happen
	mixinWorkingScope.toIndependentWorkingCopy();

The toIndependentWorkingCopy ensures that second call does not see imported variables. Solution: the joinIfIndependent method needs to work differently for local calls.