enable build-on-save when a 'check' step is found

suggested in #1918

Note that this doesn't work in VS Code until the config option are synced again.
The `enable_build_on_save` can be explicitly set to `false` to disable this behavior.

schema.json

@@ -15,9 +15,9 @@
             "default": true
         },
         "enable_build_on_save": {
-            "description": "Whether to enable build-on-save diagnostics",
+            "description": "Whether to enable build-on-save diagnostics. Will be automatically enabled if the `build.zig` has declared a 'check' step.",
             "type": "boolean",
-            "default": false
+            "default": null
         },
         "build_on_save_args": {
             "description": "Specify which arguments should be passed to Zig when running build-on-save.\n\nIf the `build.zig` has declared a 'check' step, it will be preferred over the default 'install' step.",

src/Config.zig

@@ -10,8 +10,8 @@ enable_snippets: bool = true,
 /// Whether to enable function argument placeholder completions
 enable_argument_placeholders: bool = true,
 
-/// Whether to enable build-on-save diagnostics
-enable_build_on_save: bool = false,
+/// Whether to enable build-on-save diagnostics. Will be automatically enabled if the `build.zig` has declared a 'check' step.
+enable_build_on_save: ?bool = null,
 
 /// Specify which arguments should be passed to Zig when running build-on-save.
 ///

src/Server.zig

@@ -945,7 +945,7 @@ pub fn updateConfiguration(
         server.document_store.cimports.clearAndFree(server.document_store.allocator);
 
         if (std.process.can_spawn and
-            server.config.enable_build_on_save and
+            server.config.enable_build_on_save != false and
             server.client_capabilities.supports_publish_diagnostics)
         {
             try server.pushJob(.run_build_on_save);
@@ -1018,7 +1018,7 @@ pub fn updateConfiguration(
         }
     }
 
-    if (server.config.enable_build_on_save) {
+    if (server.config.enable_build_on_save orelse false) {
         if (!std.process.can_spawn) {
             log.info("'enable_build_on_save' is ignored because your OS can't spawn a child process", .{});
         } else if (server.status == .initialized and server.config.zig_exe_path == null) {
@@ -1354,7 +1354,7 @@ fn saveDocumentHandler(server: *Server, arena: std.mem.Allocator, notification:
     }
 
     if (std.process.can_spawn and
-        server.config.enable_build_on_save and
+        server.config.enable_build_on_save != false and
         server.client_capabilities.supports_publish_diagnostics)
     {
         try server.pushJob(.run_build_on_save);

src/features/diagnostics.zig

@@ -267,6 +267,10 @@ pub fn generateBuildOnSaveDiagnostics(
         }
     }
 
+    if (!(server.config.enable_build_on_save orelse has_check_step)) {
+        return;
+    }
+
     if (has_check_step) {
         std.debug.assert(!has_explicit_steps);
         try argv.append(arena, "check");

src/tools/config.json

@@ -14,9 +14,9 @@
         },
         {
             "name": "enable_build_on_save",
-            "description": "Whether to enable build-on-save diagnostics",
-            "type": "bool",
-            "default": false
+            "description": "Whether to enable build-on-save diagnostics. Will be automatically enabled if the `build.zig` has declared a 'check' step.",
+            "type": "?bool",
+            "default": null
         },
         {
             "name": "build_on_save_args",

src/tools/config_gen.zig

@@ -16,17 +16,17 @@ const ConfigOption = struct {
     default: std.json.Value,
 
     fn getTypescriptType(self: ConfigOption) error{UnsupportedType}![]const u8 {
-        return if (std.mem.eql(u8, self.type, "[]const []const u8"))
+        std.debug.assert(self.type.len != 0);
+        const ty = self.type[@intFromBool(self.type[0] == '?')..];
+        return if (std.mem.eql(u8, ty, "[]const []const u8"))
             "array"
-        else if (std.mem.eql(u8, self.type, "[]const u8"))
+        else if (std.mem.eql(u8, ty, "[]const u8"))
             "string"
-        else if (std.mem.eql(u8, self.type, "?[]const u8"))
-            "string"
-        else if (std.mem.eql(u8, self.type, "bool"))
+        else if (std.mem.eql(u8, ty, "bool"))
             "boolean"
-        else if (std.mem.eql(u8, self.type, "usize"))
+        else if (std.mem.eql(u8, ty, "usize"))
             "integer"
-        else if (std.mem.eql(u8, self.type, "enum"))
+        else if (std.mem.eql(u8, ty, "enum"))
             "string"
         else
             error.UnsupportedType;
@@ -276,7 +276,8 @@ fn generateVSCodeConfigFile(allocator: std.mem.Allocator, config: Config, path:
             .description = option.description,
             .@"enum" = option.@"enum",
             .format = if (std.mem.indexOf(u8, option.name, "path") != null) "path" else null,
-            .default = default,
+            // "enable_build_on_save" need to be explicitly set to 'null' so that it doesn't default to 'false'
+            .default = default orelse .null,
         });
     }