Add showConfig tsc flag for debugging configs

Author: weswigham

src/compiler/commandLineParser.ts

@@ -164,6 +164,13 @@ namespace ts {
             category: Diagnostics.Command_line_Options,
             description: Diagnostics.Stylize_errors_and_messages_using_color_and_context_experimental
         },
+        {
+            name: "showConfig",
+            type: "boolean",
+            category: Diagnostics.Command_line_Options,
+            isCommandLineOnly: true,
+            description: Diagnostics.Print_the_final_configuration_instead_of_building
+        },
 
         // Basic
         {

src/compiler/diagnosticMessages.json

@@ -1007,6 +1007,10 @@
         "category": "Error",
         "code": 1349
     },
+    "Print the final configuration instead of building.": {
+        "category": "Message",
+        "code": 1350
+    },
 
     "Duplicate identifier '{0}'.": {
         "category": "Error",

src/compiler/types.ts

@@ -4443,6 +4443,7 @@ namespace ts {
         /*@internal*/ version?: boolean;
         /*@internal*/ watch?: boolean;
         esModuleInterop?: boolean;
+        /* @internal */ showConfig?: boolean;
 
         [option: string]: CompilerOptionsValue | TsConfigSourceFile | undefined;
     }

src/tsc/tsc.ts

@@ -132,6 +132,50 @@ namespace ts {
         const commandLineOptions = commandLine.options;
         if (configFileName) {
             const configParseResult = parseConfigFileWithSystem(configFileName, commandLineOptions, sys, reportDiagnostic)!; // TODO: GH#18217
+            if (commandLineOptions.showConfig) {
+                const getCanonicalFileName = createGetCanonicalFileName(sys.useCaseSensitiveFileNames);
+                const files = map(
+                    filter(
+                        configParseResult.fileNames,
+                        !configParseResult.configFileSpecs ? _ => false : matchesSpecs(
+                            configFileName,
+                            configParseResult.configFileSpecs.validatedIncludeSpecs,
+                            configParseResult.configFileSpecs.validatedExcludeSpecs
+                        )
+                    ),
+                    f => getRelativePathFromFile(getNormalizedAbsolutePath(configFileName!, sys.getCurrentDirectory()), f, getCanonicalFileName)
+                );
+                const config = {
+                    compilerOptions: {
+                        ...Object.keys(configParseResult.options).map((key) => {
+                            const value = configParseResult.options[key];
+                            const option = getOptionFromName(key);
+                            if (!option) {
+                                return [key, value] as [keyof CompilerOptions, {} | undefined];
+                            }
+                            return [key, unencodeCompilerOption(value, option, getCanonicalFileName)] as [keyof CompilerOptions, {} | undefined];
+                        }).reduce((prev, cur) => ({...prev, [cur[0]]: cur[1]}), {}),
+                        showConfig: undefined,
+                        configFile: undefined,
+                        configFilePath: undefined,
+                        help: undefined,
+                        init: undefined,
+                        listFiles: undefined,
+                        listEmittedFiles: undefined,
+                        project: undefined,
+                    },
+                    references: map(configParseResult.projectReferences, r => ({...r, path: r.originalPath, originalPath: undefined})),
+                    files: length(files) ? files : undefined,
+                    ...(configParseResult.configFileSpecs ? {
+                        include: filterSameAsDefaultInclude(configParseResult.configFileSpecs.validatedIncludeSpecs),
+                        exclude: configParseResult.configFileSpecs.validatedExcludeSpecs
+                    } : {}),
+                    compilerOnSave: !!configParseResult.compileOnSave ? true : undefined
+                }
+                // tslint:disable-next-line:no-null
+                sys.write(JSON.stringify(config, null, 4) + sys.newLine);
+                return sys.exit(ExitStatus.Success);
+            }
             updateReportDiagnostic(configParseResult.options);
             if (isWatchSet(configParseResult.options)) {
                 reportWatchModeWithoutSysSupport();
@@ -153,6 +197,53 @@ namespace ts {
         }
     }
 
+    function unencodeCompilerOption(value: any, option: CommandLineOption, getCanonicalFileName: ReturnType<typeof createGetCanonicalFileName>): {} | undefined {
+        switch (option.type) {
+            case "object":
+            case "number":
+            case "boolean":
+                return value;
+            case "string":
+                if (option.isFilePath) {
+                    return getRelativePathFromFile(sys.getCurrentDirectory(), getNormalizedAbsolutePath(value as string, sys.getCurrentDirectory()), getCanonicalFileName);
+                }
+                return value;
+            case "list":
+                const elementType = (option as CommandLineOptionOfListType).element;
+                return isArray(value) ? value.map(v => unencodeCompilerOption(v, elementType, getCanonicalFileName)) : undefined;
+            default:
+                return forEachEntry(option.type, (optionEnumValue, optionStringValue) => {
+                    if (optionEnumValue === value) {
+                        return optionStringValue;
+                    }
+                });
+        }
+    }
+
+    function filterSameAsDefaultInclude(specs: ReadonlyArray<string> | undefined) {
+        if (!length(specs)) return undefined;
+        if (length(specs) !== 1) return specs;
+        if (specs![0] === "**/*") return undefined;
+        return specs;
+    }
+
+    function matchesSpecs(path: string, includeSpecs: ReadonlyArray<string> | undefined, excludeSpecs: ReadonlyArray<string> | undefined): (path: string) => boolean {
+        if (!includeSpecs) return _ => false;
+        const patterns = getFileMatcherPatterns(path, excludeSpecs, includeSpecs, sys.useCaseSensitiveFileNames, sys.getCurrentDirectory());
+        const excludeRe = patterns.excludePattern && getRegexFromPattern(patterns.excludePattern, sys.useCaseSensitiveFileNames);
+        const includeRe = patterns.includeFilePattern && getRegexFromPattern(patterns.includeFilePattern, sys.useCaseSensitiveFileNames);
+        if (includeRe) {
+            if (excludeRe) {
+                return path => includeRe.test(path) && !excludeRe.test(path);
+            }
+            return path => includeRe.test(path);
+        }
+        if (excludeRe) {
+            return path => !excludeRe.test(path);
+        }
+        return _ => false;
+    }
+
     function reportWatchModeWithoutSysSupport() {
         if (!sys.watchFile || !sys.watchDirectory) {
             reportDiagnostic(createCompilerDiagnostic(Diagnostics.The_current_host_does_not_support_the_0_option, "--watch"));