Regression in 3.49.0: global vars can be resolved before dotenv is loaded, causing fallback to override dotenv value #2722

Description

There appears to be a regression in Task 3.49.0 related to the interaction between global vars and dotenv.

With the Taskfile below, Task 3.48.0 resolves IMAGE_TAG from the dotenv file and prints XXXX, but Task 3.49.0 resolves the fallback default and prints ABC.

This looks like global vars are being resolved too early, before dotenv values are merged into the taskfile environment.

Analysis
The behavior seems to come from a change in the variable resolution flow introduced by commit:

2cdd7d3

Commit message:

fix: Call ReplaceVars() to resolve Ref's for imported global vars. (#2632)

The likely sequence is:

During setup, Task reads dotenv files by first calling GetTaskfileVariables().

In 3.49.0, GetTaskfileVariables() now calls ReplaceVars() on c.TaskfileVars and writes the resolved values back into the compiler state.

That causes this global var to be resolved too early:

At that moment, the dotenv file has not yet been merged into the environment, so the expression resolves to ABC.

Later, dotenv is loaded, but the stored global var has already been rewritten to the fallback value, so task execution still sees ABC.

In 3.48.0, this early mutation did not happen, so once dotenv was merged, task compilation could still resolve IMAGE_TAG to XXXX.

Why This Looks Like a Regression
This changes previously working behavior for a valid configuration pattern:

Before 3.49.0: global vars could still observe values coming from global dotenv files
In 3.49.0: the same global vars can become fixed to their fallback values before dotenv is applied
That makes the behavior externally incompatible across versions.

Suspected Fix Direction
A likely fix would be to avoid mutating stored global taskfile vars during the early GetTaskfileVariables() phase, or otherwise ensure dotenv values are available before global vars are permanently resolved.

Notes
This seems related to the imported global Ref fix from #2632, but the change also affects dotenv-backed global var resolution.

Version

3.49.0

Operating system

both linux and mac os

Experiments Enabled

No response

Example Taskfile

version: '3'


vars:
  IMAGE_TAG: '{{ .IMAGE_TAG | default "ABC" }}'

dotenv:
- Taskfile.env

tasks:
  test:
    cmds:
    - echo "{{.IMAGE_TAG}}"



# > cat Taskfile.env
# IMAGE_TAG=XXXX