Add map[string]T support for config fields #7

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opened 2026-09-20 15:05:03 +00:00 by agent · 0 comments

agent commented

2026-09-20 15:05:03 +00:00

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Problem

Config fields of type map[string]string, map[string]int, etc. are silently ignored during load and write. This is a common config pattern (custom labels, env maps, feature flags).

Currently, tag.go only inspects struct fields for the conf tag. Maps are not handled in:

load.go loadFromPath — shadow type builder doesn't handle maps
write.go buildMarshalOutput / toMarshalValue — maps go through v.Interface() but without proper key mapping
env.go — no map support

Requirements

Loading: map[string]string fields should decode from TOML tables, YAML maps, and JSON objects
Writing: map[string]T fields should be serialized back to the correct format
Env vars: Not needed for maps (env var overlay doesn't make sense for map keys)
Conf tags: Maps should use the field's conf:"name" as the key in the config file

Example

type AppConfig struct {
    Labels map[string]string `conf:"labels"`
}

[labels]
environment = "production"
team = "platform"

Scope

core/tag.go — shadow type builder needs to handle reflect.Map
core/load.go — loadFromPath / copyStructFields need map copy support
core/write.go — toMarshalValue / structToMap need map handling
Tests for round-trip, nested maps, empty maps

Verification

go test -run TestMap ./...
go test -run TestMap ./... -count=1

## Problem Config fields of type `map[string]string`, `map[string]int`, etc. are silently ignored during load and write. This is a common config pattern (custom labels, env maps, feature flags). Currently, `tag.go` only inspects struct fields for the `conf` tag. Maps are not handled in: - `load.go` `loadFromPath` — shadow type builder doesn't handle maps - `write.go` `buildMarshalOutput` / `toMarshalValue` — maps go through `v.Interface()` but without proper key mapping - `env.go` — no map support ## Requirements 1. **Loading**: `map[string]string` fields should decode from TOML tables, YAML maps, and JSON objects 2. **Writing**: `map[string]T` fields should be serialized back to the correct format 3. **Env vars**: Not needed for maps (env var overlay doesn't make sense for map keys) 4. **Conf tags**: Maps should use the field's `conf:"name"` as the key in the config file ## Example ```go type AppConfig struct { Labels map[string]string `conf:"labels"` } ``` ```toml [labels] environment = "production" team = "platform" ``` ## Scope - `core/tag.go` — shadow type builder needs to handle `reflect.Map` - `core/load.go` — `loadFromPath` / `copyStructFields` need map copy support - `core/write.go` — `toMarshalValue` / `structToMap` need map handling - Tests for round-trip, nested maps, empty maps ## Verification ```bash go test -run TestMap ./... go test -run TestMap ./... -count=1 ```

agent referenced this issue

2026-09-20 15:05:26 +00:00

Add Known Limitations section to README #10

agent added the

proj-config-lib

tier-2-medium

labels

2026-09-20 15:05:50 +00:00

agent referenced this issue

2026-09-20 15:06:03 +00:00

Plan: Fix config library issues (priority order) #3

agent referenced this issue