Fix casing of module locations to match that used by Rollup. (#999)

* Fix casing of module locations to match that used by Rollup.

* Add test for case sensitivity of install entrypoints.

* Add comment pointing to PR.

snowpack/src/commands/install.ts

@@ -92,7 +92,9 @@ function resolveWebDependency(dep: string): DependencyLoc {
     const isJSFile = ['.js', '.mjs', '.cjs'].includes(path.extname(dep));
     return {
       type: isJSFile ? 'JS' : 'ASSET',
-      loc: require.resolve(dep, {paths: [cwd]}),
+      // For details on why we need to call fs.realpathSync.native here and other places, see
+      // https://github.com/pikapkg/snowpack/pull/999.
+      loc: fs.realpathSync.native(require.resolve(dep, {paths: [cwd]})),
     };
   }
   // If dep is a path within a package (but without an extension), we first need
@@ -128,7 +130,7 @@ function resolveWebDependency(dep: string): DependencyLoc {
   const [depManifestLoc, depManifest] = resolveDependencyManifest(dep, cwd);
   if (!depManifest) {
     try {
-      const maybeLoc = require.resolve(dep, {paths: [cwd]});
+      const maybeLoc = fs.realpathSync.native(require.resolve(dep, {paths: [cwd]}));
       return {
         type: 'JS',
         loc: maybeLoc,
@@ -182,7 +184,7 @@ function resolveWebDependency(dep: string): DependencyLoc {
   try {
     return {
       type: 'JS',
-      loc: require.resolve(path.join(depManifestLoc || '', '..', foundEntrypoint)),
+      loc: fs.realpathSync.native(require.resolve(path.join(depManifestLoc || '', '..', foundEntrypoint))),
     };
   } catch (err) {
     // Type only packages! Some packages are purely for TypeScript (ex: csstypes).

snowpack/src/util.ts

@@ -109,7 +109,7 @@ export function resolveDependencyManifest(dep: string, cwd: string): [string | n
   // include a package.json. If we detect that to be the reason for failure,
   // move on to our custom implementation.
   try {
-    const depManifest = require.resolve(`${dep}/package.json`, {paths: [cwd]});
+    const depManifest = fs.realpathSync.native(require.resolve(`${dep}/package.json`, {paths: [cwd]}));
     return [depManifest, require(depManifest)];
   } catch (err) {
     // if its an export map issue, move on to our manual resolver.
@@ -125,7 +125,7 @@ export function resolveDependencyManifest(dep: string, cwd: string): [string | n
   // established & move out of experimental mode.
   let result = [null, null] as [string | null, any | null];
   try {
-    const fullPath = require.resolve(dep, {paths: [cwd]});
+    const fullPath = fs.realpathSync.native(require.resolve(dep, {paths: [cwd]}));
     // Strip everything after the package name to get the package root path
     // NOTE: This find-replace is very gross, replace with something like upath.
     const searchPath = `${path.sep}node_modules${path.sep}${dep.replace('/', path.sep)}`;