feat(gatsby): Enable source maps when compiling Gatsby files in development (#36450)

Author: Auspicus

docs/docs/debugging-the-build-process.md

@@ -95,6 +95,10 @@ We won't go in depth here about how to debug in VS Code - for that you can check
       "request": "launch",
       "program": "${workspaceRoot}/node_modules/.bin/gatsby",
       "args": ["develop"],
+      "env": {
+        "PARCEL_WORKERS": "0",
+        "GATSBY_CPU_COUNT": "1",
+      },
       "runtimeArgs": ["--nolazy"],
       "console": "integratedTerminal"
     },
@@ -104,6 +108,10 @@ We won't go in depth here about how to debug in VS Code - for that you can check
       "request": "launch",
       "program": "${workspaceRoot}/node_modules/.bin/gatsby",
       "args": ["build"],
+      "env": {
+        "PARCEL_WORKERS": "0",
+        "GATSBY_CPU_COUNT": "1",
+      },
       "runtimeArgs": ["--nolazy"],
       "console": "integratedTerminal"
     }
@@ -126,6 +134,10 @@ We won't go in depth here about how to debug in VS Code - for that you can check
         "program": "${workspaceRoot}/node_modules/gatsby/dist/bin/gatsby"
       },
       "args": ["develop"],
+      "env": {
+        "PARCEL_WORKERS": "0",
+        "GATSBY_CPU_COUNT": "1",
+      },
       "runtimeArgs": ["--nolazy"],
       "console": "integratedTerminal"
     },
@@ -138,6 +150,10 @@ We won't go in depth here about how to debug in VS Code - for that you can check
         "program": "${workspaceRoot}/node_modules/gatsby/dist/bin/gatsby"
       },
       "args": ["build"],
+      "env": {
+        "PARCEL_WORKERS": "0",
+        "GATSBY_CPU_COUNT": "1",
+      },
       "runtimeArgs": ["--nolazy"],
       "console": "integratedTerminal"
     }

packages/gatsby/src/utils/parcel/compile-gatsby-files.ts

@@ -41,7 +41,7 @@ export function constructParcel(siteRoot: string, cache?: Cache): Parcel {
       root: {
         outputFormat: `commonjs`,
         includeNodeModules: false,
-        sourceMap: false,
+        sourceMap: process.env.NODE_ENV === `development`,
         engines: {
           node: _CFLAGS_.GATSBY_MAJOR === `5` ? `>= 18.0.0` : `>= 14.15.0`,
         },