Add sources to the report output

The diagnose report output now contains information about which
source provides a given configuration value (when that source
is not `default`), and which other sources, if any, also provide
the given configuration value.

This brings the diagnose report output's behaviour regarding
sources in line with that of the Ruby and Elixir integration.

packages/nodejs/.changesets/output-configuration-sources-in-diagnose-report.md

@@ -0,0 +1,5 @@
+---
+bump: "patch"
+---
+
+Add information about the sources of each configuration value in the output of the diagnose report.

packages/nodejs/src/cli/diagnose.ts

@@ -5,6 +5,7 @@ const path = require("path")
 const util = require("util")
 const readline = require("readline")
 import { HashMap } from "@appsignal/types"
+import { AppsignalOptions } from ".."
 
 export class Diagnose {
   #diagnose: typeof DiagnoseTool
@@ -149,12 +150,7 @@ export class Diagnose {
 
     this.print_newline()
 
-    console.log(`Configuration`)
-    Object.keys(data["config"]["options"])
-      .sort()
-      .forEach(key => {
-        console.log(`  ${key}: ${format_value(data["config"]["options"][key])}`)
-      })
+    this.printConfiguration(data["config"])
 
     this.print_newline()
 
@@ -349,6 +345,80 @@ export class Diagnose {
     }
   }
 
+  printConfiguration(
+    {options, sources}: {
+      options: { [key: string]: any },
+      sources: { [source: string]: { [key: string]: any } }
+    }
+  ) {
+    console.log(`Configuration`)
+    Object.keys(options)
+      .sort()
+      .forEach(key => {
+        let keySources = this.configurationKeySources(key, sources)
+
+        switch (Object.keys(keySources).length) {
+          case 0:
+            if (key == 'log_file_path') {
+              // The `log_file_path` configuration key is generated after
+              // the config is read and does not belong to any sources.
+              // Since it is derived from `log_path`, let's give it the
+              // same source as `log_path`'s final value.
+              const logPathSources = Object.keys(
+                this.configurationKeySources('log_path', sources)
+              )
+              // `log_path` has a default value, so it always has at least
+              // one source. The sources are inserted in the order they are
+              // processed, so the last one overrides the others.
+              const logPathSource = logPathSources[logPathSources.length - 1]
+              keySources[logPathSource] = options[key]
+            } else {
+              // This branch should not be executed. But if it does,
+              // let's pretend this key comes from the default source.
+              keySources["default"] = options[key]
+            }
+            // Intentional absence of `break` so that the value is printed
+            // by the next `case`.
+          case 1:
+            const source = Object.keys(keySources)[0]
+
+            let extra = ""
+            if (source !== "default") {
+              extra = ` (Loaded from: ${source})`
+            }
+
+            console.log(`  ${key}: ${format_value(options[key])}${extra}`)
+            break;
+          default:
+            console.log(`  ${key}: ${format_value(options[key])}`)
+            console.log(`    Sources:`)
+            const maxSourceLength = Object.keys(keySources)
+              // Adding one to account for the `:` after the source name.
+              .map(source => source.length + 1)
+              .reduce((max, source) => Math.max(max, source), 0);
+
+            Object.entries(keySources).forEach(([source, value]) => {
+              source = `${source}:`.padEnd(maxSourceLength, ' ')
+              console.log(`      ${source} ${format_value(value)}`)
+            })
+        }
+      })
+  }
+
+  configurationKeySources(
+    key: string,
+    sources: { [source: string]: { [key: string]: any } }
+  ) : { [source: string]: any } {
+    return Object.entries(sources)
+      .reduce((keySources, [source, sourceOptions]) => {
+        if (sourceOptions.hasOwnProperty(key)) {
+          return {...keySources, [source]: sourceOptions[key]}
+        } else {
+          return keySources
+        }
+      }, {})
+  }
+
   print_newline() {
     console.log(``)
   }