Wrong day when populating activity heapmap

[dpedu]

• Gitea version (or commit ref): 1.9.0+dev-221-g4508380cf
• Git version: 2.20.1
• Operating system: Ubuntu 14.04
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL) - https://try.gitea.io/dpedu?tab=activity
  • No
  • Not relevant
• Log gist: No messages that correlate with this activity are logged on my instance.

Description

When I perform some contributing-like activity on a Gitea instance (such as pushing commits, creating a repo, etc), Gitea populates a graphical heatmap of activity shown on my account's profile.

Gitea often highlights the wrong day when this is done. Seen screenshots.

On try.gitea.io, I performed the following steps to produce the screenshot below:

• Created an account on May 8 at around 8:50 AM Pacific time
• Created an empty repo.

The site correctly shows this on my profile, Joined on May 08, 2019. However, the heatmap put this activity under May 7th instead of the 8th, labeling me as a time traveler.

I use Gitea's official docker image - https://hub.docker.com/r/gitea/gitea/, which exhibits the same problem. I was unable to find any gitea config file settings relevant to time zones or time offsets. Gitea did not obey either setting the TZ env var (to America/Los_Angeles) nor /etc/localtime nor /etc/timezone.

The expected result is that contributions show up on the day they were actually pushed into gitea.

Screenshots

[jolheiser]

Same as #6087?