fix: provide better error message for tsconfig parsing

src/io.rs

@@ -1,36 +1,11 @@
 use anyhow::Context;
 use std::fs::File;
-use std::io::{BufWriter, Read, Write};
+use std::io::Read;
 use std::path::Path;
 
 use anyhow::Result;
 
-use serde::{Deserialize, Serialize};
-
-// REFACTOR: this belongs in a different file
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq)]
-pub struct TypescriptProjectReference {
-    pub path: String,
-}
-
-// REFACTOR: this belongs in a different file
-#[derive(Serialize, PartialEq, Eq)]
-pub struct TypescriptParentProjectReference {
-    pub files: Vec<String>,
-    pub references: Vec<TypescriptProjectReference>,
-}
-
-pub fn write_project_references<P: AsRef<Path>>(
-    path: P,
-    references: &TypescriptParentProjectReference,
-) -> Result<()> {
-    let file = File::create(&path)?;
-    let mut writer = BufWriter::new(file);
-    serde_json::to_writer_pretty(&mut writer, references)?;
-    writer.write_all(b"\n")?;
-    writer.flush()?;
-    Ok(())
-}
+use serde::Deserialize;
 
 pub(crate) fn read_json_from_file<T>(filename: &Path) -> Result<T>
 where

src/link.rs

@@ -1,18 +1,17 @@
 use std::collections::HashMap;
 use std::path::PathBuf;
 
-use anyhow::{anyhow, bail, Result};
+use anyhow::{bail, Result};
 
 use pathdiff::diff_paths;
 
 use crate::configuration_file::ConfigurationFile;
-use crate::io::{
-    write_project_references, TypescriptParentProjectReference, TypescriptProjectReference,
-};
 use crate::monorepo_manifest::MonorepoManifest;
 use crate::opts;
 use crate::package_manifest::PackageManifest;
-use crate::typescript_config::TypescriptConfig;
+use crate::typescript_config::{
+    TypescriptConfig, TypescriptParentProjectReference, TypescriptProjectReference,
+};
 
 fn key_children_by_parent(
     mut accumulator: HashMap<PathBuf, Vec<String>>,
@@ -35,17 +34,14 @@ fn key_children_by_parent(
     accumulator
 }
 
-fn create_project_references(mut children: Vec<String>) -> TypescriptParentProjectReference {
+fn create_project_references(mut children: Vec<String>) -> Vec<TypescriptProjectReference> {
     // Sort the TypeScript project references for deterministic file contents.
     // This minimizes diffs since the tsconfig.json files are stored in version control.
     children.sort_unstable();
-    TypescriptParentProjectReference {
-        files: Vec::new(),
-        references: children
-            .into_iter()
-            .map(|path| TypescriptProjectReference { path })
-            .collect(),
-    }
+    children
+        .into_iter()
+        .map(|path| TypescriptProjectReference { path })
+        .collect()
 }
 
 fn vecs_match<T: PartialEq>(a: &[T], b: &[T]) -> bool {
@@ -54,7 +50,7 @@ fn vecs_match<T: PartialEq>(a: &[T], b: &[T]) -> bool {
 }
 
 // Create a tsconfig.json file in each parent directory to an internal package.
-// This permits us to build the monorepo from the top down.
+// This permits us to compile the monorepo from the top down.
 fn link_children_packages(opts: &opts::Link, lerna_manifest: &MonorepoManifest) -> Result<bool> {
     let mut is_exit_success = true;
 
@@ -66,19 +62,10 @@ fn link_children_packages(opts: &opts::Link, lerna_manifest: &MonorepoManifest)
         .try_for_each(|(directory, children)| -> Result<()> {
             let desired_project_references = create_project_references(children);
             let tsconfig_filename = opts.root.join(&directory).join("tsconfig.json");
-            let tsconfig = TypescriptConfig::from_directory(&opts.root, &directory)?;
-            let current_project_references = tsconfig
-                .contents
-                .get("references")
-                .map(|value| {
-                    serde_json::from_value::<Vec<TypescriptProjectReference>>(value.clone())
-                        .expect("Value starting as JSON should be serializable as JSON")
-                })
-                .unwrap_or_default();
-            let needs_update = !vecs_match(
-                &current_project_references,
-                &desired_project_references.references,
-            );
+            let mut tsconfig =
+                TypescriptParentProjectReference::from_directory(&opts.root, &directory)?;
+            let current_project_references = tsconfig.contents.references;
+            let needs_update = !current_project_references.eq(&desired_project_references);
             if !needs_update {
                 return Ok(());
             }
@@ -92,7 +79,8 @@ fn link_children_packages(opts: &opts::Link, lerna_manifest: &MonorepoManifest)
                 println!("{}", serialized);
                 Ok(())
             } else {
-                write_project_references(tsconfig_filename, &desired_project_references)
+                tsconfig.contents.references = desired_project_references;
+                tsconfig.write()
             }
         })?;
 
@@ -150,14 +138,10 @@ fn link_package_dependencies(opts: &opts::Link, lerna_manifest: &MonorepoManifes
                 }
 
                 // Update the current tsconfig with the desired references
-                tsconfig
-                    .contents
-                    .as_object_mut()
-                    .ok_or_else(|| anyhow!("Expected tsconfig.json to contain an Object"))?
-                    .insert(
-                        String::from("references"),
-                        serde_json::to_value(desired_project_references)?,
-                    );
+                tsconfig.contents.insert(
+                    String::from("references"),
+                    serde_json::to_value(desired_project_references)?,
+                );
 
                 Ok(Some(tsconfig))
             },

src/typescript_config.rs

@@ -2,15 +2,94 @@ use std::fs::File;
 use std::io::{BufReader, BufWriter, Write};
 use std::path::{Path, PathBuf};
 
-use anyhow::Result;
+use anyhow::{Context, Result};
+use indoc::formatdoc;
+use serde::{Deserialize, Serialize};
 
 use crate::configuration_file::ConfigurationFile;
+use crate::io::read_json_from_file;
+
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq)]
+pub struct TypescriptProjectReference {
+    pub path: String,
+}
+
+#[derive(Debug, Serialize, Deserialize, PartialEq, Eq)]
+pub struct TypescriptParentProjectReferenceFile {
+    /// This list is expected to be empty, but must be present to satisfy the
+    /// TypeScript compiler.
+    #[serde(default)]
+    pub files: Vec<String>,
+    #[serde(default)]
+    pub references: Vec<TypescriptProjectReference>,
+}
+
+pub struct TypescriptParentProjectReference {
+    monorepo_root: PathBuf,
+    directory: PathBuf,
+    pub contents: TypescriptParentProjectReferenceFile,
+}
+
+impl ConfigurationFile<TypescriptParentProjectReference> for TypescriptParentProjectReference {
+    const FILENAME: &'static str = "tsconfig.json";
+
+    fn from_directory(
+        monorepo_root: &Path,
+        directory: &Path,
+    ) -> Result<TypescriptParentProjectReference> {
+        let filename = monorepo_root.join(directory).join(Self::FILENAME);
+        let manifest_contents: TypescriptParentProjectReferenceFile =
+            read_json_from_file(&filename).with_context(|| {
+                formatdoc!(
+                    "
+                    Unexpected contents in {:?}
+
+                    I'm trying to parse the following property and value out
+                    of this tsconfig.json file:
+
+                    - references: {{ path: string }}[]
+
+                    and the following value, if present:
+
+                    - files: string[]
+                    ",
+                    filename
+                )
+            })?;
+        Ok(TypescriptParentProjectReference {
+            monorepo_root: monorepo_root.to_owned(),
+            directory: directory.to_owned(),
+            contents: manifest_contents,
+        })
+    }
+
+    fn directory(&self) -> PathBuf {
+        self.directory.to_owned()
+    }
+
+    fn path(&self) -> PathBuf {
+        self.directory.join(Self::FILENAME)
+    }
+
+    fn write(&self) -> Result<()> {
+        let file = File::create(
+            self.monorepo_root
+                .join(&self.directory)
+                .join(Self::FILENAME),
+        )?;
+        let mut writer = BufWriter::new(file);
+        serde_json::to_writer_pretty(&mut writer, &self.contents)?;
+        writer.write_all(b"\n")?;
+        writer.flush()?;
+        Ok(())
+    }
+}
 
 pub struct TypescriptConfig {
     // FIXME: how many times do we need to duplicate this value?
     monorepo_root: PathBuf,
     directory: PathBuf,
-    pub contents: serde_json::Value,
+    pub contents: serde_json::Map<String, serde_json::Value>,
 }
 
 impl ConfigurationFile<TypescriptConfig> for TypescriptConfig {