Added config feature "reportAssertAlwaysTrue". It flags errant assert statements.

client/schemas/pyrightconfig.schema.json

@@ -258,6 +258,12 @@
       "title": "Controls reporting calls to 'cast' that are unnecessary",
       "default": "none"
     },
+    "reportAssertAlwaysTrue": {
+      "$id": "#/properties/reportAssertAlwaysTrue",
+      "$ref": "#/definitions/diagnostic",
+      "title": "Controls reporting assert expressions that will always evaluate to true",
+      "default": "none"
+    },
     "pythonVersion": {
       "$id": "#/properties/pythonVersion",
       "type": "string",

docs/configuration.md

@@ -96,6 +96,8 @@ The following settings control pyright’s diagnostic output (warnings or errors
 
 **reportUnnecessaryCast** [boolean or string, optional]: Generate or suppress diagnostics for 'cast' calls that are statically determined to be unnecessary. Such calls are sometimes indicative of a programming error. The default value for this setting is 'none'.
 
+**reportAssertAlwaysTrue** [boolean or string, optional]: Generate or suppress diagnostics for 'assert' statement that will provably always assert. This can be indicative of a programming error. The default value for this setting is 'warning'.
+
 
 ## Execution Environment Options
 Pyright allows multiple “execution environments” to be defined for different portions of your source tree. For example, a subtree may be designed to run with different import search paths or a different version of the python interpreter than the rest of the source base.

server/src/analyzer/checker.ts

@@ -386,7 +386,18 @@ export class Checker extends ParseTreeWalker {
             this._getTypeOfExpression(node.exceptionExpression);
         }
 
-        this._getTypeOfExpression(node.testExpression);
+        const type = this._getTypeOfExpression(node.testExpression);
+        if (type.category === TypeCategory.Object) {
+            if (ClassType.isBuiltIn(type.classType, 'Tuple') && type.classType.typeArguments) {
+                if (type.classType.typeArguments.length > 0) {
+                    this._evaluator.addDiagnosticForTextRange(this._fileInfo,
+                        this._fileInfo.diagnosticSettings.reportAssertAlwaysTrue,
+                        DiagnosticRule.reportAssertAlwaysTrue,
+                        `Assert expression always evaluates to true`, node.testExpression);
+                }
+            }
+        }
+
         return true;
     }
 

server/src/common/configOptions.ts

@@ -146,6 +146,9 @@ export interface DiagnosticSettings {
     // Report calls to cast that are statically determined
     // to always unnecessary.
     reportUnnecessaryCast: DiagnosticLevel;
+
+    // Report assert expressions that will always evaluate to true.
+    reportAssertAlwaysTrue: DiagnosticLevel;
 }
 
 export function cloneDiagnosticSettings(
@@ -198,7 +201,8 @@ export function getDiagLevelSettings() {
         DiagnosticRule.reportUnknownMemberType,
         DiagnosticRule.reportCallInDefaultInitializer,
         DiagnosticRule.reportUnnecessaryIsInstance,
-        DiagnosticRule.reportUnnecessaryCast
+        DiagnosticRule.reportUnnecessaryCast,
+        DiagnosticRule.reportAssertAlwaysTrue
     ];
 }
 
@@ -236,7 +240,8 @@ export function getStrictDiagnosticSettings(): DiagnosticSettings {
         reportUnknownMemberType: 'error',
         reportCallInDefaultInitializer: 'none',
         reportUnnecessaryIsInstance: 'error',
-        reportUnnecessaryCast: 'error'
+        reportUnnecessaryCast: 'error',
+        reportAssertAlwaysTrue: 'error'
     };
 
     return diagSettings;
@@ -276,7 +281,8 @@ export function getDefaultDiagnosticSettings(): DiagnosticSettings {
         reportUnknownMemberType: 'none',
         reportCallInDefaultInitializer: 'none',
         reportUnnecessaryIsInstance: 'none',
-        reportUnnecessaryCast: 'none'
+        reportUnnecessaryCast: 'none',
+        reportAssertAlwaysTrue: 'warning'
     };
 
     return diagSettings;
@@ -623,7 +629,12 @@ export class ConfigOptions {
             // Read the "reportUnnecessaryCast" entry.
             reportUnnecessaryCast: this._convertDiagnosticLevel(
                 configObj.reportUnnecessaryCast, DiagnosticRule.reportUnnecessaryCast,
-                defaultSettings.reportUnnecessaryCast)
+                defaultSettings.reportUnnecessaryCast),
+
+            // Read the "reportAssertAlwaysTrue" entry.
+            reportAssertAlwaysTrue: this._convertDiagnosticLevel(
+                configObj.reportAssertAlwaysTrue, DiagnosticRule.reportAssertAlwaysTrue,
+                defaultSettings.reportAssertAlwaysTrue)
         };
 
         // Read the "venvPath".

server/src/common/diagnosticRules.ts

@@ -42,5 +42,6 @@ export const enum DiagnosticRule {
     reportUnknownMemberType = 'reportUnknownMemberType',
     reportCallInDefaultInitializer = 'reportCallInDefaultInitializer',
     reportUnnecessaryIsInstance = 'reportUnnecessaryIsInstance',
-    reportUnnecessaryCast = 'reportUnnecessaryCast'
+    reportUnnecessaryCast = 'reportUnnecessaryCast',
+    reportAssertAlwaysTrue = 'reportAssertAlwaysTrue'
 }

server/src/tests/checker.test.ts

@@ -673,6 +673,24 @@ test('UnnecessaryCast', () => {
     validateResults(analysisResults, 1);
 });
 
+test('AssertAlwaysTrue', () => {
+    const configOptions = new ConfigOptions('.');
+
+    // By default, this is reported as a warning.
+    let analysisResults = TestUtils.typeAnalyzeSampleFiles(['assert1.py'], configOptions);
+    validateResults(analysisResults, 0, 1);
+
+    // Enable it as an error.
+    configOptions.diagnosticSettings.reportAssertAlwaysTrue = 'error';
+    analysisResults = TestUtils.typeAnalyzeSampleFiles(['assert1.py'], configOptions);
+    validateResults(analysisResults, 1, 0);
+
+    // Turn off the diagnostic.
+    configOptions.diagnosticSettings.reportAssertAlwaysTrue = 'none';
+    analysisResults = TestUtils.typeAnalyzeSampleFiles(['assert1.py'], configOptions);
+    validateResults(analysisResults, 0, 0);
+});
+
 test('RevealedType1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['revealedType1.py']);
 

server/src/tests/samples/assert1.py

@@ -0,0 +1,6 @@
+# This sample tests the ability to detect errant assert calls
+# that are always true - the "reportAssertAlwaysTrue" option.
+
+# This should generate a warning
+assert (1 != 2, "Error message")
+