add a flag that enforces boolean expressions where booleans are expected #7306

Activity

1. RyanCavanaugh commented on Feb 29, 2016

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Feb 29, 2016

   Member

   More actions

   This would be extremely non-idiomatic for JavaScript (as in, I expect almost no codebases to successfully compile under such a flag). I think TSLint would be the place for a rule like this.
2. basarat commented on Mar 1, 2016

   

   Basarat Ali Syed (basarat)

   on Mar 1, 2016

   Contributor

   More actions

   Agree with ryan. Just today :

   

   It is highly idiomatic to do such checks in JSX/TSX/React 🌹
3. Mohamed Hegazy (mhegazy)

   added

   SuggestionAn idea for TypeScriptAn idea for TypeScript

   Out of ScopeThis idea sits outside of the TypeScript language design constraintsThis idea sits outside of the TypeScript language design constraints

   on Mar 1, 2016
4. Mohamed Hegazy (mhegazy)

   closed this as completedon Mar 1, 2016
5. myitcv commented on Mar 4, 2016

   

   Paul Jolly (myitcv)

   on Mar 4, 2016

   More actions

   Aleksey-Bykov palantir/tslint#253 (amongst others)

   This is blocked on palantir/tslint#680 however
6. zpdDG4gta8XKpMCd commented on Mar 4, 2016

   

   ZpdDG4gta (zpdDG4gta8XKpMCd)

   on Mar 4, 2016

   Author

   More actions

   Paul Jolly (@myitcv) Thanks for letting me know. We at our project stopped using TsLint for this exact reason, the rules can only validate the syntax, not the semantics. We developed a homemade rule runner that gets a type checker and runs against the a type checked code of the whole application rather than an AST of a single file.

   It would not be a problem to put such rule together.
7. myitcv commented on Mar 5, 2016

   

   Paul Jolly (myitcv)

   on Mar 5, 2016

   More actions

   Aleksey-Bykov in the absence of support for this kind of rule in tslint have you shared your custom rule runner?
8. zpdDG4gta8XKpMCd commented on Mar 5, 2016

   

   ZpdDG4gta (zpdDG4gta8XKpMCd)

   on Mar 5, 2016

   Author

   More actions

   I cannot share the real runner, but I can outline how to make one:

   import * as ts from 'typescript';
   import * as fs from 'fs';
   
   export function run(
       projectFileOrFolder: string
   ): void {
   
       const options: ts.CompilerOptions = {
           project: projectFileOrFolder
       };
   
       const host = tlb.toCompilerHost(options);
   
       const program = ts.createProgram(
           [],
           options,
           host
       );
   
       const emitted = program.emit();
       if (emitted.diagnostics.length > 0) { throw new Error('program has problems'); }
   
       const checker = program.getTypeChecker();
       const rootFileNames = program.getRootFileNames();
   
       rootFileNames.map(rootFileName => {
           const rootNode = program.getSourceFile(rootFileName);
           analyze(rootNode, checker);
       });
   }
   
   function analyze(rootNode: ts.Node, checker: ts.TypeChecker): void {
      // TODO: put your rule here
   }
   
   function toCompilerHost(
       options: ts.CompilerOptions
   ): ts.CompilerHost {
       return {
           readFile: (fileName: string): string => {
               return fs.readFileSync(fileName, 'utf8');
           },
           fileExists: (fileName: string): boolean => {
               return fs.existsSync(fileName);
           },
           getSourceFile: function (filepath: string) {
               try {
                   return ts.createSourceFile(
                       filepath,
                       fs.readFileSync(filepath, 'utf8'),
                       options.target,
                       true
                   );
               }
               catch (e) {
                   return undefined;
               }
           },
           writeFile: () => null,
           getDefaultLibFileName: () => 'lib.d.ts',
           useCaseSensitiveFileNames: () => true,
           getCanonicalFileName: (filename: string) => filename,
           getCurrentDirectory: () => '',
           getNewLine: () => '\n'
       };
   }
9. zpdDG4gta8XKpMCd commented on Mar 5, 2016

   

   ZpdDG4gta (zpdDG4gta8XKpMCd)

   on Mar 5, 2016

   Author

   More actions

   then comes the simplified rule

   function analyze(rootNode: ts.Node, checker: ts.TypeChecker): void {
       visitEachNode(rootNode, node => {
           if (node.kind === ts.SyntaxKind.IfStatement) {
              checkIfStatement(<ts.IfStatement>node, checker);
           } else if (node.kind === ts.SyntaxKind.ConditionalExpression) {
              checkConditionalExpression(<ts.ConditionalExpression>node, checker);
           }
       });   
   }
   
   function checkIfStatement(node: ts.IfStatement, checker: ts.TypeChecker): void {
       var type = checker.getTypeAtLocation(node.expression);
       if ((type.flags & ts.TypeFlags.Boolean) !== ts.TypeFlags.Boolean) {
           console.warn('if expression is not boolean');
       }
   }
   
   function checkConditionalExpression(node: ts.ConditionalExpression, checker: ts.TypeChecker): void {
       var type = checker.getTypeAtLocation(node.condition);
       if ((type.flags & ts.TypeFlags.Boolean) !== ts.TypeFlags.Boolean) {
           console.warn('if expression is not boolean');
       }
   }
   
   function visitEachNode(rootNode: ts.Node, visit: (node: ts.Node) => void): void {
       ts.forEachChild(rootNode, child => {
           visit(child);
           visitEachNode(child, visit);
       });
   }
10. zpdDG4gta8XKpMCd commented on Mar 5, 2016

    

    ZpdDG4gta (zpdDG4gta8XKpMCd)

    on Mar 5, 2016

    Author

    More actions

    also take a look at the official example on how to make a linter: https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#traversing-the-ast-with-a-little-linter
11. myitcv commented on Mar 6, 2016

    

    Paul Jolly (myitcv)

    on Mar 6, 2016

    More actions

    Aleksey-Bykov thanks for the pointers
12. microsoft

    locked and limited conversation to collaborators on Jun 19, 2018