fix(sdk-trace-base): don't load envs top level

Right now `@opentelemetry/sdk-trace-base` loads `OTEL_*` env vars when it is loaded, regardless of if `loadDefaultConfig` is ever called. In runtimes with a permission model like Deno, this may cause a bunch of permission prompts right on startup. This PR changes the env vars to all be loaded when `loadDefaultConfig` is called.

Interestingly, previously only `buildSamplerFromEnv` used the "global" env vars. For all other options the env vars are re-read on every call to `loadDefaultConfig`.

packages/opentelemetry-sdk-trace-base/src/config.ts

@@ -22,7 +22,6 @@ import { AlwaysOnSampler } from './sampler/AlwaysOnSampler';
 import { ParentBasedSampler } from './sampler/ParentBasedSampler';
 import { TraceIdRatioBasedSampler } from './sampler/TraceIdRatioBasedSampler';
 
-const env = getEnv();
 const FALLBACK_OTEL_TRACES_SAMPLER = TracesSamplerValues.AlwaysOn;
 const DEFAULT_RATIO = 1;
 
@@ -36,23 +35,23 @@ const DEFAULT_RATIO = 1;
 // object needs to be wrapped in this function and called when needed otherwise
 // envs are parsed before tests are ran - causes tests using these envs to fail
 export function loadDefaultConfig() {
-  const _env = getEnv();
+  const env = getEnv();
 
   return {
     sampler: buildSamplerFromEnv(env),
     forceFlushTimeoutMillis: 30000,
     generalLimits: {
-      attributeValueLengthLimit: _env.OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT,
-      attributeCountLimit: _env.OTEL_ATTRIBUTE_COUNT_LIMIT,
+      attributeValueLengthLimit: env.OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT,
+      attributeCountLimit: env.OTEL_ATTRIBUTE_COUNT_LIMIT,
     },
     spanLimits: {
-      attributeValueLengthLimit: _env.OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT,
-      attributeCountLimit: _env.OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT,
-      linkCountLimit: _env.OTEL_SPAN_LINK_COUNT_LIMIT,
-      eventCountLimit: _env.OTEL_SPAN_EVENT_COUNT_LIMIT,
+      attributeValueLengthLimit: env.OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT,
+      attributeCountLimit: env.OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT,
+      linkCountLimit: env.OTEL_SPAN_LINK_COUNT_LIMIT,
+      eventCountLimit: env.OTEL_SPAN_EVENT_COUNT_LIMIT,
       attributePerEventCountLimit:
-        _env.OTEL_SPAN_ATTRIBUTE_PER_EVENT_COUNT_LIMIT,
-      attributePerLinkCountLimit: _env.OTEL_SPAN_ATTRIBUTE_PER_LINK_COUNT_LIMIT,
+        env.OTEL_SPAN_ATTRIBUTE_PER_EVENT_COUNT_LIMIT,
+      attributePerLinkCountLimit: env.OTEL_SPAN_ATTRIBUTE_PER_LINK_COUNT_LIMIT,
     },
     mergeResourceWithDefaults: true,
   };