(1) Background

To fix following issue:

• Add "contains" operator in where function to support list pages in nested subdir

I implemented a new contains operator in Hugo where function in following PR:

• tpl: Add "contains" operator in where tpl function

(2) How Hugo where function works

Basically Hugo where function use the checkCondition() function to check if the given field value matches the match value or not. The complete codes in: "/tpl/collections/where.go"

• v: given field value, represents as reflect.Value
• mv: match value, also reprsents as reflect.Value
• ivp: the pointer of integer type of given filed value
• imvp: the pointer of integer type of match value
• svp: the pointer of string type of give filed value
• smvp: the pointer of string type of match value
• iva: a interger array converts from a given field value
• sva: a strign array converts from a given field value

1. Firstly, it gets the real value it points to if v or mv is a pointer or interface, indirect() defined in "./tpl/collections/apply.go"
2. if it can deference the v or mv, compare them with those basic operators
3. if it detected that v or mv is boolean value, just compare them
4. convert given field value and match value and stores to correpsonding varaibles
5. based on variables it generates, execute operate corresponding logic

Here, I take In operation as an example. when given field is basic type, e,g: string, and match value is a slice, it does below logic:

1. check if match value is a slice or array, if not, return false
2. if match value is zero length, return false
3. if child item’s type in match value(now it is array or slice) doesn’t match the given field value’s type, return false
4. convert given field value and storge information into correspdoning variables
5. if given field value is a interger, then ivp is not nil, and by logic above, the match value is a interger slice, so a interger array iva build from match value slice should be generated already,
   use function In to compare the given field value in match value array or not
6. if given field value is a string, then svp is not nil, here match value can be a string or string list, compare use In function too

(3) New contains operator implementaion logic

1. Make sure given field value is either Slice, Array or String and try to converts given field value information to ivp, svp, slv
2. Make sure given field value length is larger than 0
3. If given field value is Slice or Array, then make sure the child item of given field is the same type as the match value
4. Converts the match value and store nessary information to imvp,smvp, slmv,
5. If given field value is Slice or Array and child item is TimeType, try to converts the given field value and match value to ima and iva, in other words, converts the timeType to int64 array
6. Finally, evaluate the contaings logic with below logic:
   • if iva is not nil which means the given field is an interger array, check if iva(interger array of give value) contains imvp(interger match value)
   • if smvp is not nil which means the match value is a string, then check below logic
   • if sva length larger than 0 which means given field is a string array, check if sva(string array of given value) contains smvp(string match value)
   • else if sva is 0 but svp is not nil, which means given field is a string, check if spv(string of given value) contains substring smvp(string match value)
   • if slv and slmv is not nil, which means given value and match value are all either Slice or Array, then check below logic:
   • check if iva larger than 0, which means given value can converts to a timeType array, then we check if each item in ima(interger array of match value) are all in iva(interger array of give value), return true if all contains in given value, return false is it fails
   • above logic should returns if the child item in give value array is timeType, now for other types of child item, we just check with the Hugo In function

(4) How to apply the patch

1. Firstly, create the corresponding build path for hugo project

   # mkdir -p /path/to/GOROOT/src/github.com/gohugoio/
   # cd /path/to/GOROOT/src/github.com/gohugoio/
   # git clone https://github.com/gohugoio/hugo.git

2. Switch to the release you want to apply the patch, e,g: release-0.37

   # git checkout release-0.37

3. Download the patch: https://patch-diff.githubusercontent.com/raw/gohugoio/hugo/pull/4132.patch and put into git project dir

   # git apply --stat 4132.patch
   # git apply --check 4132.patch
   # git am --signoff < 4132.patch

4. Download and get mage compile tool ready, build hugo binary

   # go get github.com/magefile/mage
   # mage vendor
   # mage hugo

5. The builded binary hugo file can be found in /path/to/GOROOT/src/github.com/gohugoio/hugo/hugo